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Skin and hair

Everything in the library studied for it, medical and holistic together. Within each kind, what was shown to help comes first, strongest evidence first. What was tested and not shown to help stays on the list.

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Medication31 Peptides and SARMs3 Supplements18 Therapies2 Practices2 Daily life1

Medication

FinasterideStrongStudied in men

Scalp hair count and appearance

Shown to raise vertex hair count in men by about 107 hairs at 1 year and 138 at 2 years over placebo, from a baseline of 876.

The numbers and sources

Effect: On finasteride 1 mg, hair count in a 5.1 cm² area of the vertex rose by 107 hairs at 1 year and 138 hairs at 2 years against placebo, from a baseline of 876. The placebo group lost hair progressively [1]. Pooled, men on finasteride were more likely to report improved scalp hair in the short term (RR 1.81, 95% CI 1.42 to 2.32) and long term (RR 1.71, 95% CI 1.15 to 2.53). Mean hair count rose 9.42% more than placebo by 12 months and 24.3% more by 24 months or later. The number needed to treat for one man to rate himself improved was 5.6 short term and 3.4 long term [2].
Population: 1,553 men aged 18 to 41 over 1 year, and 1,215 in a second-year extension [1]; 12 RCTs with 3,927 men [2].
Sources: [1], [2]
Caveats: [2] rated the evidence moderate quality. Short-term self-assessment results were heterogeneous (I² 64%). The trials studied men, not women.

IsotretinoinStrong

Severe and moderate acne

Shown to reduce acne lesions more than placebo or oral antibiotics, ranking first of 37 interventions in a network analysis of 221 trials.

Compared with placebo or oral antibiotics [1]; other acne treatments in a network analysis of 37 interventions [2]

The numbers and sources

Effect: Across 11 trials, isotretinoin always reduced lesion counts more than its control, which was placebo in 2, oral antibiotics in 7 and another treatment in 2 [1]. A network meta-analysis ranked oral isotretinoin first for percentage reduction in total lesions, with a mean difference of 48.41, ahead of triple combinations of a topical retinoid, benzoyl peroxide and an antibiotic [2]. In the Absorica label trial, 70% reached a 90% reduction in nodules after 20 weeks [3].
Population: 760 people with mostly moderate to severe acne, mostly men, mean age 18 to 47.9 [1]; 65,601 patients in 221 trials [2]; 925 people aged 12 to 54 with severe nodular acne [3].
Sources: [1], [2], [3]
Caveats: In the trials with low risk of bias, 2 of 3 showed a significant difference from control [1]. The label trial compared two isotretinoin products, with no placebo arm [3].

MinoxidilStrongStudied in womenVery common

Hair regrowth in women, topical

Shown to roughly double reported hair regrowth in women over placebo, adding about 13 hairs per cm². The 2% and 5% strengths did not differ.

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: Moderate to marked self-rated regrowth was reported by 157 of 593 on minoxidil and 77 of 555 on placebo (RR 1.93, 95% CI 1.51 to 2.47). Investigator ratings agreed (RR 2.35, 95% CI 1.68 to 3.28). Total hair count rose 13.18 hairs per cm² more than placebo (95% CI 10.92 to 15.44). Minoxidil 2% and 5% did not differ in regrowth [1]. A second meta-analysis also found 2% minoxidil raised hair growth against placebo in women [2].
Population: 47 trials with 5,290 women, 17 of them on minoxidil [1]; good or fair quality RCTs to December 2016 [2].
Sources: [1], [2]
Caveats: Only 5 of 47 trials in [1] were at low risk of bias. Evidence for hair count was rated low quality [1]. [2] reported high heterogeneity.

Tretinoin and topical retinoidsStrongVery common

Acne

Shown to clear more acne than vehicle, with 16% to 21% clear or almost clear at 12 weeks on adapalene against 9% on vehicle.

Compared with vehicle cream or gel [1][2][3][4]; antibiotics and other acne drugs in a network analysis [5]

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: In the adapalene label trial, 21% on 0.3% gel and 16% on 0.1% gel were rated clear or almost clear at 12 weeks against 9% on vehicle, and total lesions fell 45.3%, 41.8% and 33.7% [2]. In two tazarotene 0.1% cream trials, 18% and 20% had no or minimal acne against 11% and 6% on vehicle, and total lesions fell a median 44% and 42% against 24% and 21% [3]. A systematic review of 54 trials found topical retinoids superior to vehicle on global assessments [1]. A network meta-analysis of 221 trials found topical retinoids comparable to oral or topical antibiotics for inflammatory lesions, and ranked combinations of a topical retinoid, benzoyl peroxide and an antibiotic behind only oral isotretinoin [5]. Tazarotene 0.045% lotion raised treatment success against vehicle (OR 2.1) [4].
Population: 653 people aged 12 to 52 with mild to moderate acne [2]; 424 and 411 people aged 12 and over in two trials [3]; 54 trials from 2008 to 2018 [1]; 65,601 patients in 221 trials, mean age 20.4, median 12 weeks [5]; 6 phase 3 trials in moderate to severe acne [4].
Sources: [5], [1], [2], [3], [4]
Caveats: Most trials ran 12 weeks. Most people on the drug did not reach clear or almost clear skin in the label trials [2][3]. The network analysis abstract gives no effect size for retinoids against vehicle [5].

Antibiotics (common outpatient)Moderate

Acne (doxycycline)

Shown to reduce acne lesions, with doxycycline beating placebo in a 16-week trial and matching azithromycin in meta-analyses. Spironolactone did better than doxycycline in adult women.

Compared with placebo and doxycycline 100 mg [10]; azithromycin [11][12]; isotretinoin and other treatments [12]; spironolactone [13]

The numbers and sources

Effect: Modified-release doxycycline 40 mg was superior to placebo for inflammatory lesions and success rate over 16 weeks, comparable to doxycycline 100 mg, with fewer drug-related side effects than 100 mg [10]. Azithromycin pulses and daily doxycycline did not differ in remaining lesions or assessments at 12 weeks, with more stops for side effects on doxycycline [11]. Across 23 trials, doxycycline matched azithromycin (OR 1.28, 95% CI 0.54 to 3.04), while other treatments such as isotretinoin improved acne grading scores more, and doxycycline had more gastrointestinal and skin side effects [12]. In adult women with moderate acne, spironolactone was more successful than doxycycline at 4 and 6 months [13].
Population: 662 people aged 12 or older with moderate to severe acne [10]; 906 patients in 6 trials [11]; 2,672 patients in 23 trials [12]; 133 women [13].
Sources: [10], [11], [12], [13]
Caveats: The placebo trial abstract gives no effect sizes [10], and heterogeneity was high in [12].

AntihistaminesModerate

Chronic hives

Shown to clear chronic hives completely more often than placebo, about 2.7 times as often with cetirizine 10 mg, in evidence drawn from few studies.

Compared with placebo [4][1]; other antihistamines [4]

The numbers and sources

Effect: Cetirizine 10 mg once daily led to complete suppression of urticaria more often than placebo (RR 2.72, 95% CI 1.51 to 4.91). Levocetirizine 5 mg beat placebo in the intermediate term but not the short term, and desloratadine results had very wide intervals. More people had complete suppression on cetirizine than on fexofenadine. Withdrawals for adverse events did not differ significantly [4]. In two 4-week label trials, levocetirizine 2.5, 5 and 10 mg lowered itch scores more than placebo, with fewer and smaller wheals [1].
Population: 9,759 participants in 73 studies [4]; 423 adults aged 18 to 85 with chronic idiopathic urticaria [1].
Sources: [4], [1]
Caveats: Most comparisons rest on few studies or single-study estimates [4].

FinasterideModerate

Adding topical minoxidil

Shown to improve photographic hair scores more with topical minoxidil added than either drug alone in androgenetic alopecia. Hair density change did not differ.

The numbers and sources

Effect: Across 5 RCTs, finasteride plus topical minoxidil produced higher global photographic scores, more patients with marked improvement and fewer with no change or worsening than either drug alone. Hair density change and adverse events did not differ between the combination and either drug alone [3].
Population: 5 RCTs in people with androgenetic alopecia, 2 of them comparing the combination with finasteride alone [3].
Sources: [3]
Caveats: One meta-analysis of few trials. The abstract gives P values without effect sizes, and concentrations varied [3].

FinasterideModerateStudied in men

Topical finasteride

Shown to raise hair density and hair count in men, as a mix with minoxidil and as a spray at 24 weeks. No topical finasteride is FDA-approved.

The numbers and sources

Effect: Across 7 RCTs, a topical solution of minoxidil mixed with finasteride raised hair density (mean difference 9.22, P 0.04), hair diameter (mean difference 2.26, P 0.005) and global photographic scores (mean difference 0.79) more than minoxidil solution alone. Marked improvement was more likely on the mix (OR 3.29) [4]. In a 24-week phase 3 trial, topical finasteride spray raised target-area hair count more than placebo at week 24 (P under 0.05) but not at week 12 (P 0.0688). Terminal hair count and investigator-rated vertex growth also favored the spray [5].
Population: 7 RCTs with 396 men [4]; 270 Chinese men, 251 completing, randomized 2 to 1 to spray or placebo [5].
Sources: [4], [5]
Caveats: The authors of [4] rate the main results moderate certainty and note heterogeneity and small samples. The abstract of [5] gives P values without effect sizes. No topical finasteride is FDA-approved, and the products sold in the US are compounded (see Risks) [6].

Hormonal birth controlModerateStudied in women

Acne

Shown to reduce acne lesions and severity in women more than placebo, in all nine placebo-controlled trials with data, across several progestin types.

Compared with placebo, other combined pills and an antibiotic [4]

The numbers and sources

Effect: Every placebo-controlled trial found fewer acne lesions and lower severity. A levonorgestrel pill cut total lesions by about 10 (MD -9.98, 95% CI -16.51 to -3.45) and a norgestimate pill by 9.32. Clear or almost clear skin was more likely on a drospirenone pill (OR 3.02). Differences between progestins were less clear [4]. The drospirenone pill Yaz is FDA-approved for moderate acne in women who also want contraception [2].
Population: 12,579 participants in 31 trials [4].
Sources: [4], [2]
Caveats: Data for any single comparison between pills were limited [4].

IsotretinoinModerate

Rosacea

Shown to reduce rosacea lesions and redness at low doses, more than topical retinoids or antimicrobials, in an off-label use with 35% relapse within 6 months of stopping.

Compared with before treatment, and topical retinoids or topical antimicrobials [6]

The numbers and sources

Effect: Isotretinoin at 0.5 mg/kg/day or less reduced lesion count and redness with a large effect (SMD above 0.8). Against topical retinoids and antimicrobials, it reduced lesions more (SMD above 0.5). Lesion count and redness stayed 70% and 47% lower 16 weeks after stopping. Relapse was 35% at 5.5 months, and 0.4% had serious adverse events [6].
Population: 1,445 patients in 16 randomized and non-randomized studies [6].
Sources: [6]
Caveats: Study designs varied, which limited comparisons [6]. Rosacea is not an FDA-approved use.

MinoxidilModerateStudied in men

Hair regrowth in men, topical

Shown to raise hair growth over placebo in men at 2% and 5%, though in indirect comparisons finasteride 1 mg added more hair than either.

The numbers and sources

Effect: Both 2% and 5% topical minoxidil raised hair growth against placebo in men [2]. In a network meta-analysis, 1 mg finasteride raised terminal hair count at 48 weeks by 32.1 hairs per cm² more than 2% topical minoxidil and 26.2 more than 5% [3].
Population: RCTs in men with androgenetic alopecia [2]; 23 studies in men [3].
Sources: [2], [3]
Caveats: The abstract of [2] reports significance without effect sizes. High heterogeneity [2].

MinoxidilModerate

Beard and facial hair, topical

Shown to raise beard and mustache density over placebo, about 11 more beard hairs per cm², in one trial in transgender men on testosterone.

The numbers and sources

Effect: A systematic review of 19 RCTs of minoxidil for facial hair reported more facial hair growth with few side effects. Five trials were at high risk of bias and six at low risk [6]. In a 12-week trial of topical 3% minoxidil, beard density rose 11.16 hairs per cm² against 0.08 on placebo, and mustache density 18.45 against 1.74. Beard and mustache hair diameter also rose more than on placebo. Adverse events were similar between groups [7].
Population: 19 RCTs [6]; 69 transgender men on stable testosterone therapy [7].
Sources: [6], [7]
Caveats: The abstract of [6] gives no pooled effect size. [7] studied people on testosterone therapy, so it may not apply to others.

SpironolactoneModerateStudied in womenVery common

Acne in women

Shown to improve acne in adult women against placebo, with 82% against 63% reporting improvement at 24 weeks in one trial.

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: In women with facial acne, the acne-specific quality of life symptom score (range 0 to 30) at 12 weeks was 19.2 on spironolactone and 17.8 on placebo (adjusted difference 1.27, 95% CI 0.07 to 2.46), and at 24 weeks 21.2 against 17.4 (difference 3.45, 95% CI 2.16 to 4.75). Improvement was reported by 72% against 68% at 12 weeks and 82% against 63% at 24 weeks (OR 2.72, 95% CI 1.50 to 4.93). Investigator-rated treatment success at 12 weeks was 19% against 6% [9]. In a second trial, spironolactone had better treatment success at 6 months than doxycycline given for 3 months (P = 0.007) [10].
Population: 410 women aged 18 and over with facial acne for at least 6 months, mean age 29.2 [9]; 133 women with moderate acne, all also using benzoyl peroxide [10].
Sources: [9], [10]
Caveats: The difference at 12 weeks was small, and participants could keep using topical treatment [9]. An older Cochrane review could not pool acne data because single trials reported each outcome [11]. Not an FDA-approved use [3].

SpironolactoneModerate

Hirsutism

Shown to lower hirsutism scores in women by about 7.7 points on the Ferriman-Gallwey scale against placebo, in small trials rated low quality.

The numbers and sources

Effect: A Cochrane review found spironolactone 100 mg a day lowered Ferriman-Gallwey scores more than placebo (MD -7.69, 95% CI -10.12 to -5.26), and did about as well as flutamide and finasteride in two studies each [12]. An earlier Cochrane review found that in two trials of 100 mg against placebo, women more often reported improvement in hair growth (OR 7.18, 95% CI 1.96 to 26.28) [11].
Population: Women with hirsutism within a review of 157 studies and 10,550 women, each study of 30 to 80 people [12]; two small placebo-controlled trials [11].
Sources: [12], [11]
Caveats: Low quality evidence from small trials, most at high risk of bias [12]. The two reviews draw on overlapping trials. Not an FDA-approved use [3].

Tranexamic acidModerate

Melasma

Shown to lower melasma severity scores and recurrence when oral tranexamic acid was added to a triple combination cream, against the cream alone.

Compared with triple combination cream alone [8]

The numbers and sources

Effect: Adding oral tranexamic acid lowered the Melasma Area and Severity Index more than the cream alone (MD -3.10, 95% CI -5.85 to -0.35) and lowered recurrence (RR 0.28, 95% CI 0.16 to 0.49). Erythema and burning did not differ [8].
Population: 490 patients with melasma in 4 trials [8].
Sources: [8]
Caveats: Four trials. This use is outside the US tablet label, which covers heavy menstrual bleeding [4].

H2 blockersLimited

Hives, added to an antihistamine

Small trials found adding ranitidine or cimetidine to diphenhydramine cleared hives more often than diphenhydramine alone. The evidence was old and at high or unclear risk of bias.

Compared with diphenhydramine alone [8]

The numbers and sources

Effect: Ranitidine with diphenhydramine resolved urticaria more often than diphenhydramine alone (RR 1.59, 95% CI 1.07 to 2.36). Cimetidine alone did not improve overall symptoms more than diphenhydramine, but the combination did (RR 2.02, 95% CI 1.03 to 3.94). Sedation from baseline did not differ with famotidine or diphenhydramine [8].
Population: 144 participants in 4 small studies [8].
Sources: [8]
Caveats: The review authors called the evidence very limited and rated the studies at high to unclear risk of bias. The direct evidence is for ranitidine and cimetidine, not famotidine [8].

HydroxyzineLimited

Itching

Limited evidence: hydroxyzine matched loratadine for clearing chronic hives in one comparison, and itch scores fell in a small dialysis trial with no placebo group.

The numbers and sources

Effect: In a Cochrane review of antihistamines for chronic hives, complete suppression over the short term did not differ between hydroxyzine 25 mg and loratadine 10 mg (RR 1.00, 95% CI 0.32 to 3.10) [8]. In a crossover trial in people on dialysis, itch severity on a 10-point scale fell from 6.83 to 2.86 over 6 weeks on hydroxyzine 25 mg a day and from 7.1 to 2.17 on gabapentin, with no significant difference between the two [9]. A Cochrane review found no randomized trial of an oral antihistamine used alone for eczema [10].
Population: 73 studies of antihistamines with 9,759 participants, of which one comparison involved hydroxyzine [8]; 32 patients on dialysis [9].
Sources: [8], [9], [10]
Caveats: An approved use that rests on older evidence. Neither comparison here had a placebo arm for hydroxyzine, and the hives comparison had a wide confidence interval.

MinoxidilLimited

Low-dose sublingual against placebo

Small trials found sublingual 1.35 mg twice daily raised front scalp hair count over placebo, with no change at the crown.

The numbers and sources

Effect: At 24 weeks, sublingual minoxidil 1.35 mg twice daily raised midfrontal hair count 15.7 hairs per cm² more than placebo (P 0.03). Vertex hair count did not differ. Testosterone levels did not change and no serious adverse events occurred [8]. In men in a 24-week trial, mean hair fiber diameter fell 2 µm on placebo and on 0.45 mg daily, and rose 3 µm on 1.35 mg and 6 µm on 4.05 mg in an open-label extension [9].
Population: 46 transgender people on full-dose testosterone with mild androgenetic alopecia [8]; 33 men with androgenetic alopecia, plus 12 in the extension [9].
Sources: [8], [9]
Caveats: Two small trials. The higher doses in [9] were open-label and not compared with placebo. Sublingual minoxidil is not an FDA-approved form.

SpironolactoneLimitedStudied in women

Hirsutism and cycles in PCOS

Small open-label trials in women with PCOS found hirsutism scores fell more with spironolactone than with metformin, and more with the two combined than with either alone.

Compared with metformin 1,000 mg a day [22][23]; metformin 1,700 mg a day alone [24]; spironolactone alone [23]

The numbers and sources

Effect: Over 6 months, the Ferriman-Gallwey hirsutism score fell from 12.9 to 8.7 on spironolactone 50 mg a day and from 12.5 to 10.0 on metformin. Menstrual cycles rose from 6.6 to 10.2 a year on spironolactone and from 5.7 to 9.1 on metformin (P = 0.0037). Testosterone fell in both groups, and weight and blood pressure did not change [22]. In a three-arm trial, spironolactone 50 mg plus metformin raised cycles a year and lowered hirsutism score, total testosterone and glucose and insulin area under the curve more than either drug alone (P < .05) [23]. Adding spironolactone 25 mg to metformin lowered the hirsutism score more than metformin alone (P < 0.001), while regular menses returned in 68% on the combination and 82% on metformin alone [24].
Population: 82 adolescent and young women with PCOS randomized, 69 completing, mean age 22.6 [22]; 198 women with PCOS randomized, 169 completing [23]; 56 women with PCOS [24].
Sources: [22], [23], [24]
Caveats: All three trials were open-label, small and lasted 6 months, with no placebo group. Two came from the same research group [22][23]. Not an FDA-approved use [3].

AntihistaminesModerate

Higher doses for hives that do not respond

Mixed results: raising the dose of a non-sedating antihistamine improved itch in chronic hives but did not change response rates or the number of wheals.

Compared with standard doses and placebo [5]

The numbers and sources

Effect: Response rates and wheal counts did not differ between standard and higher doses. Higher doses significantly improved the itch score of the Urticaria Activity Score [5].
Population: 15 studies of chronic spontaneous urticaria [5].
Sources: [5]
Caveats: Only five studies were of high quality, and heterogeneity was significant [5].

Hormonal birth controlModerateStudied in women

Excess hair and androgens in PCOS

Mixed results: against metformin, hair growth improved about the same in one review and more on the pill in overweight women in another.

Compared with metformin [36][37]; metformin combined with the pill [36][37]; placebo or lifestyle change [35]; other combined pills [38]

The numbers and sources

Effect: Against metformin, hirsutism did not differ, while free androgen index was 7.08 lower, SHBG 118.61 nmol/L higher and testosterone 0.48 nmol/L lower on the pill. Adding metformin to the pill lowered free androgen index and raised SHBG further [36]. A Cochrane review found metformin may improve hirsutism less than the pill in women with BMI 25 to 30 (MD 1.92, 95% CI 1.21 to 2.64), with an uncertain difference at other BMIs, and the pill plus metformin improved hirsutism more than the pill alone [37]. Hirsutism did not differ from placebo or lifestyle change, at very low certainty [35]. Pills with cyproterone acetate lowered hirsutism and testosterone (MD 0.38 nmol/L) more than conventional pills, and high and low estrogen doses did not differ [38].
Population: 36 RCTs in women with PCOS [36]; 44 RCTs with 2,253 women and adolescents with PCOS [37]; 4 RCTs [35]; 19 RCTs comparing two pills [38].
Sources: [36], [37], [35], [38]
Caveats: Cochrane evidence quality was very low to low [37]. The guideline reviewers noted the higher clot risk of cyproterone acetate pills in the general population [38].

IsotretinoinModerate

Against oral antibiotics plus topical treatment

Mixed results: in three trials, isotretinoin did not reduce inflammatory lesions more than antibiotics plus topical treatment, while physician-rated severity improved slightly.

Compared with oral antibiotics plus topical agents [4]

The numbers and sources

Effect: Against oral antibiotics plus topical agents, isotretinoin made no difference to investigator-counted inflammatory lesions (RR 1.01, 95% CI 0.96 to 1.06). It may slightly improve physician-rated severity (RR 1.15, 95% CI 1.00 to 1.32), with 67% more minor adverse effects (RR 1.67, 95% CI 1.42 to 1.98), such as dry lips and skin, cheilitis, vomiting and nausea [4].
Population: 400 people with moderate or severe acne in 3 trials, and 351 in 2 trials, treated 20 to 24 weeks, within a Cochrane review of 31 trials and 3,836 participants aged 12 to 55 [4].
Sources: [4]
Caveats: Very low to low quality evidence. All but 3 of the 31 trials had high risk of bias in at least one area, and 12 were funded by drug companies [4].

IsotretinoinModerate

Lower daily doses

Mixed results: lower daily doses cleared many lesions, but conventional doses gave more responders in one trial and longer remission in a meta-analysis of adults.

Compared with conventional doses and pulsed or intermittent regimens [4][5]

The numbers and sources

Effect: In severe acne, a 95% drop in inflammatory lesions was reached by 58% on 0.1 mg/kg/day, 80% on 0.5 and 90% on 1 mg/kg/day over 20 weeks. Another trial found lesion counts fell 79%, 80% and 84% on 0.05, 0.1 and 0.2 mg/kg/day. Continuous low or conventional doses reduced inflammatory lesions more than one week a month [4]. In adults with mild to moderate acne, conventional doses gave more response and longer remission than low daily doses, and low daily doses beat pulsed doses [5].
Population: 150 and 154 people with severe acne in single trials, and 40 with moderate acne [4]; adults with mild to moderate acne in pooled studies [5].
Sources: [4], [5]
Caveats: Heterogeneity prevented pooling in [4], and [5] rated the evidence low quality. Low-dose use for mild to moderate acne is off-label [5].

MetforminModerateStudied in women

Excess hair and androgens in PCOS

Mixed results: against the pill, hair growth improved about the same in one review and less in overweight women in another. Metformin lowered testosterone against placebo.

Compared with combined oral contraceptive pills [35][36]; metformin combined with the pill [36]; placebo [31]; lifestyle change with or without placebo [33]

The numbers and sources

Effect: Hirsutism did not differ between metformin and combined oral contraceptive pills, while free androgen index was 7.08 higher, SHBG 118.61 nmol/L lower and testosterone 0.48 nmol/L higher on metformin than on the pill [35]. In a Cochrane review, metformin may improve hirsutism less than the pill in women with BMI 25 to 30 (MD 1.92, 95% CI 1.21 to 2.64, 5 RCTs, 254 women), with an uncertain difference at other BMIs. Metformin alone and the pill alone each improved hirsutism less than the two combined [36]. Against placebo, metformin lowered total testosterone (SMD -0.33, 95% CI -0.49 to -0.17) [31]. Lifestyle change plus metformin did not differ from lifestyle change on clinical or biochemical hyperandrogenism, while metformin alone gave lower testosterone than lifestyle change [33].
Population: 36 RCTs in women with PCOS [35]; 44 RCTs with 2,253 women and adolescents with PCOS [36]; 24 RCTs with 564 women given metformin [31]; 12 RCTs with 608 women [33].
Sources: [35], [36], [31], [33]
Caveats: Cochrane evidence quality was very low to low [36]. Hirsutism scales and trial lengths varied.

MinoxidilModerate

Low-dose oral against topical

Mixed results: oral 5 mg and topical 5% did not differ in direct trials, while an indirect comparison found more hair with oral.

The numbers and sources

Effect: At 24 weeks, oral minoxidil 5 mg daily and topical 5% twice daily did not differ in terminal or total hair density on the frontal scalp. On the vertex, terminal density differed by 23.4 hairs per cm² (95% CI -0.3 to 43.0), not significant, and photographs favored oral treatment (24%, 95% CI 0 to 48) [4]. In a network meta-analysis, oral minoxidil 5 mg produced the largest rise in terminal hair count at 24 weeks, 29.8 hairs per cm² more than topical 5% [3]. A meta-analysis of 4 head-to-head trials found no difference in hair density between oral and topical minoxidil (mean difference 0.95, 95% CI -24.98 to 26.87). Terminal hair density did not differ significantly either [5].
Population: 90 men aged 18 to 55 with androgenetic alopecia, 68 completing, at one clinic in Brazil [4]; 23 studies in men [3]; 4 trials comparing oral with topical minoxidil in androgenetic alopecia [5].
Sources: [4], [3], [5]
Caveats: [4] had 24% dropout. The network estimate is indirect. The meta-analysis pooled only 4 trials, with a wide interval [5]. Few controlled trials have tested oral doses below 5 mg in men.

Tretinoin and topical retinoidsModerate

Differences between topical retinoids for acne

Mixed results: adapalene 0.1% cleared acne about as well as tretinoin 0.025%, worked faster in week 1 and irritated skin less. Tretinoin and tazarotene did not differ.

Compared with tretinoin 0.025% gel [6]; each other, in trials reviewed [1]

The numbers and sources

Effect: Across five investigator-blinded trials, adapalene 0.1% gel matched tretinoin 0.025% gel in reducing total lesions, reduced inflammatory and total lesions more at week 1, and had greater local tolerability at every visit [6]. A systematic review found no significant difference in efficacy between tretinoin and tazarotene. Adverse events occurred in 62% on tretinoin 0.05% against 19% on adapalene 0.1% and 40% on adapalene 0.3% [1].
Population: 900 people with mild to moderate acne, 450 per drug [6]; 54 trials [1].
Sources: [6], [1]
Caveats: The 1998 analysis pooled the manufacturer's own adapalene trials, published and unpublished [6]. The adverse event comparison in [1] draws on separate trials, not one head-to-head study.

MontelukastLimited

Chronic hives

Limited evidence: most trials found leukotriene blockers alone no better than placebo or antihistamines for chronic hives, while adding one to an antihistamine appeared to help more.

Compared with placebo or antihistamines [6]

The numbers and sources

Effect: Across 10 randomized trials, most found leukotriene receptor antagonists not superior to placebo or antihistamines as monotherapy, while the combination with antihistamines appeared to improve hives more than antihistamines alone. Heterogeneity was too high for a pooled analysis [6].
Population: 10 randomized or crossover trials in chronic urticaria [6].
Sources: [6]
Caveats: No pooled estimate. Trials differed in design and outcomes [6].

SpironolactoneLimitedStudied in womenVery common

Female pattern hair loss

Limited evidence: in uncontrolled studies about 43% of women improved on spironolactone alone and 44% regrew hair on an antiandrogen. No placebo-controlled result was sourced.

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: A systematic review of trials and observational studies found hair loss improved in 56.60% of women overall, 43.21% on spironolactone alone and 65.80% on combined therapy, with significant heterogeneity. Hair loss did not improve or improved modestly in 37.80% [13]. In an open before-and-after study of spironolactone 200 mg a day or cyproterone acetate for at least 12 months, 44% of women had hair regrowth, 44% had no clear change and 12% kept losing hair, with results for the two drugs combined [14].
Population: Women with female pattern hair loss in randomized and observational studies [13]; 80 women aged 12 to 79 with biopsy-confirmed hair loss, 40 on spironolactone [14].
Sources: [13], [14]
Caveats: Neither source reports a comparison with placebo, so the share that would have improved untreated is unknown. Not an FDA-approved use [3].

AntihistaminesModerate

Eczema itch, added to skin treatment

Not shown to consistently improve eczema when added to skin treatment, though fexofenadine 120 mg slightly reduced itch over one week in adults.

Compared with placebo [6]

The numbers and sources

Effect: In 795 children followed 18 months, cetirizine showed no difference from placebo in eczema symptoms and fewer adverse events (RR 0.68). In adults, fexofenadine 120 mg a day lowered itch on a 0 to 8 scale by 0.25 points (95% CI -0.43 to -0.07) over one week. Another comparison found no difference in itch on a 100-point scale [6].
Population: 3,285 participants in 25 studies, 1,941 of them children [6].
Sources: [6]
Caveats: Studies were too varied to pool, and risk of bias was mostly unclear [6].

H2 blockersLimited

Warts (cimetidine)

Small trials found cimetidine did not clear common warts more often than placebo, with 32% cured on cimetidine against 30.7% on placebo in one trial.

Compared with placebo [11][12]

The numbers and sources

Effect: After 3 months of cimetidine 25 to 40 mg/kg daily or placebo, warts were cured in 32% (9 of 28) and 30.7% (8 of 26), with no significant difference [11]. A second double-blind trial with strict entry criteria also found cimetidine not statistically better than placebo, with a possible trend in younger people. It notes earlier uncontrolled studies reporting success [12].
Population: 70 patients with multiple warts, 54 assessed [11]; adults with recalcitrant warts [12].
Sources: [11], [12]
Caveats: Small trials. Warts often clear on their own, which open-label reports cannot separate from a drug effect [12].

Low-dose naltrexoneLimited

Other autoimmune conditions

One trial found no change in disease activity over placebo in lichen planopilaris, a scarring hair loss. No trials in other autoimmune conditions were located.

The numbers and sources

Effect: In 34 patients with lichen planopilaris, an autoimmune scarring hair loss, 3 mg a day added to clobetasol cream for 6 months did not change disease activity more than placebo with clobetasol (p 0.813) [13].
Population: 34 patients analyzed by intention to treat [13].
Sources: [13]
Caveats: One small trial in one condition. No controlled trials in lupus, rheumatoid arthritis, psoriasis or thyroid disease were located.

Peptides and SARMs

KPVGrey marketUntested

Skin inflammation, psoriasis and eczema

Not studied in people. KPV is the end piece of alpha-MSH, a hormone that reduced skin inflammation in animals. No KPV study of psoriasis or eczema was located.

No study in people. This rests on how it acts in the body, lab studies.

The numbers and sources

Effect: A 2008 review reports that the anti-inflammatory effects of alpha-MSH were confirmed in animal models including irritant and allergic contact dermatitis, and that KPV, its C-terminal tripeptide, keeps the anti-inflammatory effect without alpha-MSH's pigmenting action. The authors propose KPV for future treatment of inflammatory skin disease [12]. A 2007 review attributes most of alpha-MSH's anti-inflammatory activity to KPV [13]. In human skin cells (keratinocytes) in the lab, KPV did not raise cyclic AMP, and raised intracellular calcium only when the cyclic AMP pathway was blocked [14].
Population: Animal models of skin inflammation treated with alpha-MSH, reviewed in [12]. Human keratinocytes in the lab [14].
Sources: [12], [13], [14]
Caveats: The animal skin findings in these abstracts are for alpha-MSH, the parent hormone, not for KPV itself [12][13]. No study of KPV in a psoriasis or eczema model was located for this page.

TB-500Grey marketUntested

Wound healing

Not studied in people. In aged mice, the seven amino acid TB-500 sequence sped skin wound repair comparably to full-length thymosin beta-4.

No study in people. This rests on animal studies, lab studies.

The numbers and sources

Effect: In 26-month-old mice with full-thickness skin wounds, a synthetic peptide matching thymosin beta-4's seven amino acid actin-binding domain, LKKTETQ, promoted repair comparable to that seen with the full protein [16]. In the lab, the actin-binding motif matched thymosin beta-4's activity in human endothelial cell migration and in blood vessel sprouting from chick aortic tissue, while peptides lacking any part of it were inactive [17].
Population: Aged mice [16]. Human endothelial cells and chick aortic tissue in the lab [17].
Sources: [16], [17], [12], [9]
Caveats: These studies used the LKKTETQ sequence. An analysis of one TB-500 product identified an acetylated form, Ac-LKKTETQ [12]. Mouse skin wounds do not show what happens in people, and trials of full-length thymosin beta-4 do not describe TB-500 [9].

GHK-CuGrey marketNo research yet

Hair growth

We haven't sourced research on this yet.

Supplements

ZincModerate

Wound healing

Shown to improve ulcer healing in 5 trials of people with ulcers, from moderate-quality evidence.

The numbers and sources

Effect: Across 5 clinical trials, zinc treatment was associated with better ulcer healing at the final endpoint (MD 1.41, 95% CI 1.04 to 1.92), from moderate-quality evidence [5].
Population: People with ulcers in 5 clinical trials [5].
Sources: [5]
Caveats: Only 5 trials. The abstract does not give the number of participants, the zinc route or the dose [5]. The abstract of [5] labels its pooled figure a mean difference (MD), though it reads like a ratio. It is given here as printed.

CollagenLimitedStudied in women

Hair thickness

One trial found 1,000 mg a day of fish collagen peptides increased hair diameter over 24 weeks in 114 women with thinning hair.

The numbers and sources

Effect: In 114 women aged 20 to 50 with self-reported hair thinning, 1,000 mg a day of low-molecular-weight fish collagen peptides for 24 weeks increased hair diameter against placebo at week 24 [14].
Population: 114 women [14].
Sources: [14]
Caveats: One trial of one product. No trial of nails was located.

Fish oilLimited

Skin hydration, water loss and elasticity

Small trials found krill oil and fish oil raised skin hydration and lowered water loss. The krill trials were funded by the oil supplier.

The numbers and sources

Effect: In two placebo-controlled pilot trials, krill oil at 1 g a day (51 adults) or 2 g a day (50 adults) for 12 weeks lowered transepidermal water loss (from 14.47 to 13.83 and from 14.25 to 13.02 g/m²/h) and raised skin hydration and elasticity against placebo. The changes tracked the rise in omega-3 index [38]. In 60 people on hemodialysis with severe itch, 1,000 mg of fish oil (more than 900 mg EPA) twice a day for 3 months raised skin moisture on the face and arms, which did not rise on a soybean oil placebo, and itch scores fell [39]. A meta-analysis of 61 human diet and supplement studies found that lipids and fatty acids as a group improved skin hydration (pSMD 0.54, 95% CI 0.28 to 0.80) and elasticity (pSMD 0.49, 95% CI 0.14 to 0.83) and reduced wrinkles (pSMD -0.62, 95% CI -0.92 to -0.31) [40].
Population: Healthy adults with baseline water loss of more than 10 and up to 24.9 g/m²/h [38]; adults on maintenance hemodialysis [39]; participants in 61 studies [40].
Sources: [38], [39], [40]
Caveats: Two krill trial authors are employees of Aker BioMarine, which provided the krill and placebo oils and funded the study [38]. The meta-analysis grouped all lipids and fatty acids, so it does not isolate fish oil [40]. The hemodialysis abstract reports within-group changes [39].

Fish oilLimited

Sunburn and the skin's response to UV light

Small trials found purified EPA or fish oil raised the UV dose needed to cause sunburn. Skin aging and skin cancer were not studied.

The numbers and sources

Effect: In 42 healthy adults, 4 g a day of purified EPA for 3 months raised the UV dose needed to cause sunburn from a mean 36 to 49 mJ/cm² (P < 0.01) and lowered UV-induced p53-positive skin cells from 16 to 8 per 100 epidermal cells. No change appeared on the oleic acid comparison [41]. In 20 people, 4 weeks of fish oil raised the minimal erythema dose slightly but significantly, with no change on placebo [42]. In 79 women with nickel allergy, 5 g a day of an EPA-rich lipid for 3 months reduced UV suppression of skin immunity by 6.9% against a control lipid (95% CI -2.1% to 15.9%), which was not significant. At the middle UV dose the difference was 11% (95% CI 0.5% to 21.4%) [43]. A systematic review of 47 photoprotection studies included omega-3 trials and placed the most evidence with polyphenols, carotenoids and Polypodium leucotomos [44].
Population: 42 healthy adults [41]; 20 adults [42]; 79 women aged 22 to 60 with fair skin (phototype I or II) [43]; human studies [44].
Sources: [41], [42], [43], [44]
Caveats: Small, short trials of acute UV markers, not of skin aging or skin cancer. The EPA trial reported within-group changes [41].

GlutathioneLimited

Skin lightening (oral and topical)

Small trials found a lower melanin index on sun-exposed skin with oral or topical glutathione. Reviewers rated the evidence inconclusive or at high risk of bias.

The numbers and sources

Effect: In a review of 4 studies, oral glutathione at 500 mg a day and topical 2% oxidized glutathione lowered the melanin index on sun-exposed skin. Sun-protected skin showed no significant change [4]. A 2025 review found 5 trials and one open study of oral doses of 250 to 500 mg a day that lowered the melanin index against placebo [5].
Population: Healthy volunteers in 4 studies [4]; trials in the 2025 review [5].
Sources: [4], [5]
Caveats: The 2019 authors called the evidence inconclusive, citing study quality and inconsistent findings [4]. The 2025 review rated about half the studies at high risk of bias [5].

NiacinLimited

Skin cancer prevention (nicotinamide)

One trial found 23% fewer new nonmelanoma skin cancers on nicotinamide in high-risk adults, with no benefit after stopping or in transplant recipients.

The numbers and sources

Effect: Over 12 months, new nonmelanoma skin cancers were 23% lower on nicotinamide 500 mg twice a day than on placebo (95% CI 4 to 38). Squamous-cell carcinomas were 30% lower (95% CI 0 to 51) and basal-cell carcinomas did not significantly differ. Actinic keratoses were 11% to 20% lower. No benefit remained after nicotinamide stopped [5]. A 2026 systematic review pooled 2 RCTs in organ transplant recipients (180 people) and found no significant reduction in keratinocyte cancers (rate ratio 0.97, 95% CI 0.77 to 1.22). In a retrospective cohort of 33,822 patients, nicotinamide use was associated with 14% less skin cancer overall (HR 0.86, 95% CI 0.83 to 0.89) and none in transplant recipients [6].
Population: 386 people with at least two nonmelanoma skin cancers in the past 5 years [5]; transplant recipients and a retrospective cohort [6].
Sources: [5], [6]
Caveats: The benefit in immunocompetent adults rests on one trial, in people at high risk. Funded by Australia's National Health and Medical Research Council [5]. All randomized trials followed people for 12 months or less, and certainty for transplant outcomes was low or very low [6].

ProbioticsLimitedStudied in women

Sensitive skin and barrier recovery, Lacticaseibacillus paracasei NCC 2461 (ST11)

One trial found lower skin sensitivity and faster skin barrier recovery than placebo in women taking L. paracasei NCC 2461 for 2 months.

The numbers and sources

Effect: In 64 women, 2 months of L. paracasei NCC 2461 lowered skin sensitivity to capsaicin and sped recovery of skin barrier function, measured as water loss, against placebo [46].
Population: Two groups of 32 women [46].
Sources: [46]
Caveats: One trial of one strain. The abstract gives no effect sizes [46].

Saw palmettoLimited

Hair loss

Limited evidence: small trials found more hair growth or density, often with combination products, and less growth than finasteride in one unblinded study.

The numbers and sources

Effect: A systematic review of 5 RCTs and 2 prospective cohorts of topical and oral products containing saw palmetto reported 60% improvement in overall hair quality, 27% improvement in total hair count and increased density in 83.3% of patients [5]. In an open-label 2-year study of 100 men, 38% on 320 mg saw palmetto a day had more hair growth, against 68% on 1 mg finasteride [6]. In a 6-month placebo-controlled trial of one oral extract, total terminal hair count changed by +18.6 against -10.1 on placebo, and total hair density by +25.1 against -12.2 (both p < 0.001) [7].
Population: Adults with androgenetic alopecia or telogen effluvium [5]. 100 men with mild to moderate androgenetic alopecia [6]. 60 men and women with self-perceived thinning hair, 40 on the extract and 20 on placebo [7].
Sources: [5], [6], [7]
Caveats: Many products combined saw palmetto with other ingredients [5]. The finasteride comparison had no placebo and no blinding [6]. The placebo trial tested one branded extract (SEREVELLE, Valensa International), had a single author and enrolled people by self-perceived thinning rather than diagnosis [7].

TurmericModerate

Psoriasis

Mixed results: one review reported lower psoriasis severity, but its confidence interval includes no effect. Small trials of oral and topical curcumin lowered severity.

The numbers and sources

Effect: A meta-analysis of 7 RCTs found curcumin alone or with other treatment improved PASI against controls (std. MD -0.83, p 0.02) [29]. In 63 patients with mild to moderate psoriasis on topical steroids, oral curcumin 2 g a day (Meriva) for 12 weeks lowered PASI more than steroids alone [30]. In 40 patients with scalp psoriasis, a topical turmeric tonic twice a day for 9 weeks lowered PASI and improved quality of life against placebo (P < .05) [31]. In an open trial without placebo, 4.5 g a day of oral curcuminoids gave a response rate of 16.7% (95% CI 2% to 48%) [32].
Population: Adults with plaque or scalp psoriasis [29][30][31][32].
Sources: [29], [30], [31], [32]
Caveats: The meta-analysis abstract gives a 95% CI of -1.53 to 0.14, which includes no effect, alongside p 0.02 [29]. The trials were small and mixed oral and topical forms. The open trial authors attribute its low response to placebo effect or natural history [32].

IronLimitedStudied in women

Hair loss

Linked to low iron stores: women with non-scarring hair loss had lower ferritin than women without it. No controlled trial has tested iron supplements for hair loss.

The numbers and sources

Effect: In a meta-analysis of 36 studies with 10,029 participants, women with non-scarring hair loss had ferritin 18.51 ng/dL lower than women without it (95% CI -25.85 to -11.16), and 21% had ferritin of 10 to 15 or below [16]. A 2010 review found only small studies of differing designs and no randomized treatment trial, and called for a trial of iron in iron-deficient women with hair loss [17]. In mice, iron deficiency from before birth caused hair loss in the pups, which regrew when iron was restored to the diet [18].
Population: Women with and without non-scarring hair loss in 36 studies [16]. A literature review [17]. C57BL/6J mice [18].
Sources: [16], [17], [18]
Caveats: The human evidence is observational, so low ferritin may travel with hair loss without causing it [16]. No trial shows that taking iron regrows hair in people [17]. The abstract reports ferritin in ng/dL, though ferritin is usually reported in ng/mL [16].

Vitamin CLimited

Sunburn sensitivity, oral

Small trials found vitamin C with vitamin E slightly raised the UV dose needed for sunburn, while vitamin C alone did not change UV redness.

The numbers and sources

Effect: In 10 people, 2 g of vitamin C with 1,000 IU of vitamin E a day for 8 days raised the median UV dose needed for sunburn from 80 to 96.5 mJ/cm² (p < 0.01), while it fell from 80 to 68.5 mJ/cm² on placebo [14]. In 12 volunteers, 500 mg of vitamin C a day for 8 weeks raised skin vitamin C and did not change the redness response to UV [15]. A systematic review of 47 photoprotection studies found the weakest evidence for isolated vitamin or CoQ10 supplements [16].
Population: 10 adults [14]; 12 healthy volunteers [15]; human studies [16].
Sources: [14], [15], [16]
Caveats: The positive trial combined vitamins C and E, so vitamin C's share is unknown [14]. The vitamin C only abstract describes no placebo group [15]. Both are small and short.

Fish oilStrong

Psoriasis severity

Not shown to reduce psoriasis severity on its own in adults. Added to conventional treatment, PASI scores fell about 4 points.

The numbers and sources

Effect: Across 3 RCTs (337 participants) with usable data, fish oil did not reduce PASI (MD -0.28, 95% CI -1.74 to 1.19) [18]. A review of 18 RCTs (927 participants) found fish oil alone had no effect on PASI (P 0.47), lesion area or itch. Combined with conventional treatment, PASI fell by 3.92 points (95% CI -6.15 to -1.69) [19].
Population: Adults with psoriasis [18][19].
Sources: [18], [19]
Caveats: Only 3 of 13 trials had usable data in [18].

Vitamin DStrong

Psoriasis severity

Not shown to lower psoriasis severity with oral vitamin D in adults. One small pooled effect lost significance after adjustment.

The numbers and sources

Effect: Across 3 trials, oral vitamin D lowered PASI at 6 months (MD -0.92, 95% CI -1.72 to -0.11), and the result lost significance after Hartung-Knapp adjustment (95% CI -2.21 to 0.38) [9]. Across 4 studies (333 patients), PASI, DLQI and CRP changes did not differ from control [10]. In 122 adults in Norway with low vitamin D, 100,000 IU then 20,000 IU a week for 4 months did not change PASI against placebo (adjusted difference 0.11, 95% CI -0.23 to 0.45) [11].
Population: Adults with plaque psoriasis [9][10][11].
Sources: [9], [10], [11]
Caveats: Baseline severity was low in the Norwegian trial (mean PASI 3.1) [11]. This concerns oral vitamin D, not topical vitamin D analogue creams.

Vitamin DModerateStudied in women

Excess hair and androgens in PCOS

Not shown to change hair growth scores or SHBG in women with PCOS in one review. Total testosterone fell slightly against placebo.

Compared with placebo [73]; placebo, metformin, short-acting contraceptives, ovulation drugs or assisted reproduction without vitamin D [69]

The numbers and sources

Effect: Across 13 RCTs (840 women), modified Ferriman-Gallwey hair scores (MD 0.04, 95% CI -0.79 to 0.86) and SHBG (MD 1.33, 95% CI -2.70 to 5.36) did not differ from placebo. Total testosterone fell by 0.17 (95% CI 0.05 to 0.29) and serum vitamin D rose by 17.81 [73]. A review of add-on vitamin D in women seeking pregnancy also found lower androgen levels (MD -2.31, 95% CI -3.51 to -1.11) [69].
Population: 840 women with PCOS in 13 RCTs [73]; 1,961 women with PCOS in 20 RCTs [69].
Sources: [73], [69]
Caveats: The abstract of [73] does not give units for testosterone or vitamin D. The hair score result rests on one review.

BiotinLimited

Hair growth in people without a deficiency or hair disorder

Small studies found biotin alone did not speed hair growth in healthy men, and the one placebo-controlled trial a 2024 review located found no difference in hair growth.

The numbers and sources

Effect: In a randomized, open, crossover trial in 10 healthy men with no hair disorder, 5 mg of biotin a day for 14 days did not raise the hair growth rate over baseline, which averaged 2.35 mm a week. Growth rose only when biotin was combined with topical minoxidil (p = 0.02) [10]. A 2024 review found three studies of oral biotin for hair growth or quality. The highest quality, a double-blind placebo-controlled trial, found no difference in hair growth between biotin and placebo, and the other two, in people on isotretinoin and women after sleeve gastrectomy, were open to bias with no clear result [11].
Population: 10 healthy men, median age 29.7 [10]. Three studies in a narrative review [11].
Sources: [10], [11]
Caveats: The crossover trial was tiny, open label and lasted 14 days per arm [10]. The review notes how few studies exist [11].

Coenzyme Q10Limited

Sunburn sensitivity, oral

One small trial found 12 weeks of CoQ10 did not change the UV dose that causes sunburn in 33 healthy adults.

The numbers and sources

Effect: In 33 healthy adults, 12 weeks of 50 or 150 mg a day of CoQ10 did not significantly change the minimal erythema dose, the UV dose that causes sunburn [25]. A systematic review of 47 photoprotection studies found the weakest evidence for isolated vitamin or CoQ10 supplements [27].
Population: 33 healthy adults [25]; human studies [27].
Sources: [25], [27]
Caveats: One small trial measured sunburn sensitivity directly [25].

DIMLimitedStudied in men

Hormonal acne and testosterone in men

One small trial found DIM did not significantly change testosterone in 45 men with prostate cancer. Acne has been tested only in the lab, against acne bacteria.

The numbers and sources

Effect: In 45 men awaiting prostate surgery, 21 to 28 days of DIM or placebo produced no significant change in plasma testosterone, PSA or IGF-1 measures. Only the urinary 2-hydroxyestrone to 16-hydroxyestrone ratio changed, at the higher dose [3]. In male rats given DIM for 53 days, one middle dose had an anti-androgenic effect, and higher doses lowered sperm motility and damaged testicular tissue [7]. In the lab, DIM inhibited growth and biofilm formation by Cutibacterium acnes, the main acne bacterium [8].
Population: 45 men with prostate cancer [3]. 38 Sprague Dawley rats [7]. Bacterial cultures [8].
Sources: [3], [7], [8]
Caveats: The human trial was short, in men with prostate cancer, and testosterone was a secondary measure [3]. No study of acne in people taking DIM was located. Rat and lab findings do not show what happens in people [7][8].

GlutathioneLimited

Skin lightening (IV)

One trial found lightening in 37.5% on IV glutathione against 18.7% on placebo, a difference that was not significant.

The numbers and sources

Effect: One placebo-controlled trial of IV glutathione was found. Lightening occurred in 6 of 16 on glutathione (37.5%) and 3 on placebo (18.7%), P = 0.054 [5].
Population: One trial within a systematic review [5].
Sources: [5]
Caveats: A 2016 search found no studies of IV glutathione for skin lightening and none of its safety in chronic use for any indication [6].

Therapies

PRP injectionsModerate

Pattern hair loss, compared with placebo

Shown to raise hair density in androgenetic alopecia against placebo at 3 and 6 months. Hair count and hair diameter did not differ from placebo.

Compared with placebo [13]; control groups the review abstract does not describe [14]

The numbers and sources

Effect: Across 9 trials, PRP raised hair density at 3 and 6 months against placebo (P < .05). Hair count and diameter rose from baseline and did not differ from placebo [13]. In 21 trials in women with hair loss, PRP raised hair density and thickness and reduced hairs lost on the pull test, with pain or discomfort no different from control (RR 1.01, 95% CI 0.87 to 1.18) [14].
Population: 238 patients with androgenetic alopecia in 9 trials [13]. 628 women in 21 trials [14].
Sources: [13], [14]
Caveats: Trials were small. The reviews give no pooled size for the density gain in their abstracts, and the women's review notes effects varied with dose, schedule and ethnicity [13][14].

PRP injectionsModerate

Pattern hair loss, compared with minoxidil

Mixed results: hair density, terminal hair count and regrowth did not differ from 5% minoxidil, while patient satisfaction was higher with PRP.

Compared with topical minoxidil [15]

The numbers and sources

Effect: Across 9 trials, hair density did not differ between PRP and minoxidil, and neither did terminal hair count or moderate to high regrowth. Patient satisfaction was higher with PRP than with 5% minoxidil (OR 2.77, 95% CI 1.53 to 5.04), and negative hair pull tests were more common, 82.75% against 52.94% [15].
Population: 451 men and women with androgenetic alopecia in 9 trials [15].
Sources: [15]
Caveats: Heterogeneity across studies was high [15].

Practices

Red light therapyStrong

Hair growth in pattern hair loss

Shown to increase hair density in men and women with androgenetic alopecia compared with sham devices, with large pooled effects and high variation between trials.

The numbers and sources

Effect: Across 11 double-blind RCTs, hair density rose more with low-level laser devices than with sham (SMD 1.316, 95% CI 0.993 to 1.639), in both sexes and with comb and helmet devices [3]. Across 15 studies (795 participants), the SMD for hair density was 1.02 (95% CI 0.68 to 1.36) [4]. Across 38 studies (3,098 patients, 2,930 with androgenetic alopecia), hair density rose against placebo after under 20 weeks (SMD 1.14, 95% CI 0.51 to 1.78) and over 20 weeks (SMD 1.44, 95% CI 0.97 to 1.91) [5].
Population: Adults with androgenetic alopecia in 11 RCTs [3], 15 studies [4] and 38 studies treated for 4 to 26 weeks [5].
Sources: [3], [4], [5], [2]
Caveats: Heterogeneity was high, with I² of 81% to 88% [5]. Trials measured hairs per square centimeter over weeks to months, and long-term comparisons between devices are lacking [2]. Data for other types of hair loss were too sparse to pool [5]. The abstracts do not report who funded the device trials.

Red light therapyModerate

Acne

Mixed results: red light did not differ from conventional acne treatments in pooled trials, and a Cochrane review found high-quality evidence for light therapies lacking.

The numbers and sources

Effect: Across 13 RCTs (422 participants), red light did not differ from conventional treatments in inflammatory lesions (weighted mean difference 0.701, 95% CI -0.809 to 2.212) or non-inflammatory lesions (-0.527, 95% CI -3.055 to 2.001) [21]. A Cochrane review of 71 light therapy trials (4,211 participants) could not pool most comparisons and rated the evidence very low in quality. In 3 trials (360 participants), red light with a photosensitizing cream was no different from red light with placebo cream [22]. A systematic review of 31 LED trials gave acne a grade of recommendation of B, on a scale where other skin conditions received C or D [23].
Population: 422 people with moderate to severe acne [21]. 4,211 people, mostly with mild to moderate acne and aged 20 to 30 on average [22]. 31 RCTs across skin conditions [23].
Sources: [21], [22], [23]
Caveats: No difference from another treatment is not the same as better than no treatment, and few trials used a sham. Two thirds of the Cochrane trials were industry-sponsored, and fewer than half followed people beyond 8 weeks [22].

Daily life

Pet ownershipModerateStudied in children

Eczema in children

Linked to about 28% less eczema in children exposed to dogs in one meta-analysis of birth cohorts. Cat exposure was not linked.

Compared with children not exposed to dogs, cats or pets [12]

The numbers and sources

Effect: Exposure to dogs (RR 0.72, 95% CI 0.61 to 0.85) and to pets overall (RR 0.75, 95% CI 0.67 to 0.85) was linked to less atopic dermatitis. Exposure to cats was not (RR 0.94, 95% CI 0.76 to 1.16) [12].
Population: Children in 21 birth cohorts, 26 publications, exposed during pregnancy, infancy or childhood [12].
Sources: [12]
Caveats: Observational. Families with allergies may avoid getting pets, which can make pets look protective. Heterogeneity was moderate (I² 46% for dogs) [12].