What does the research show about alpha-blockers?

Alpha-blockers

Meta-analyses found alpha-blockers lowered prostate symptom scores more than placebo, with similar effects across drugs, and raised passage of larger ureteral stones. Large trials of small stones found no difference from placebo. Dizziness and low blood pressure on standing were common, ejaculation problems were very common on silodosin, and tamsulosin was strongly linked to floppy iris during cataract surgery.

Add to Bio HackChecked 2026-11-13

Status: Prescription drugs in the US. Tamsulosin, alfuzosin and silodosin are FDA-approved for the signs and symptoms of benign prostatic hyperplasia (BPH) and are not indicated for high blood pressure. Doxazosin and terazosin are approved for both BPH and high blood pressure. Use for kidney and ureteral stones is off-label.
Also called: alpha-1 blockers, alpha-adrenergic antagonists, tamsulosin, Flomax, alfuzosin, Uroxatral, silodosin, Rapaflo, doxazosin, Cardura, Cardura XL, terazosin, Hytrin, Jalyn (dutasteride with tamsulosin)
Taken for: enlarged prostate, weak urine stream, getting up at night to urinate, passing a kidney stone, stones after lithotripsy, urinating after a catheter, chronic prostatitis, pelvic pain, high blood pressure, Parkinson disease prevention

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

Shown to help7

StrongShown to lower prostate symptom scores more than placebo in men with an enlarged prostate, by about 1 to 3 points, with small gains in urine flow.
StrongShown to raise stone passage, about 116 more per 1,000 in placebo-controlled trials, mainly for stones over 5 mm. Stones of 5 mm or less showed no clear benefit.Common
ModerateShown to raise clearance of stone fragments after lithotripsy, from 69% to about 80%, in evidence a Cochrane review rated low certainty.Very common
ModerateShown to help men urinate after catheter removal for acute urinary retention, 60% against 38% on placebo.Very common
ModerateShown to lower blood pressure about 8/5 mm Hg more than placebo in high blood pressure, which the review authors called modest and likely an overestimate.
LimitedOne trial found doxazosin cut overall BPH progression 39% against placebo over 4.5 years, but not urinary retention or the need for surgery. Doxazosin with finasteride cut it 66%.
LimitedLimited evidence: two cohort studies linked terazosin, doxazosin or alfuzosin to lower Parkinson risk or fewer Parkinson events than tamsulosin, in men. No trial has tested this.

Reported risks14

StrongShown to raise ejaculation problems, most with silodosin, 28% against 1% on placebo, and on tamsulosin 8% at 0.4 mg. Doxazosin and terazosin were similar to placebo.Very common
ModerateShown to raise dizziness and low blood pressure on standing in label trials, with dizziness in 15% on tamsulosin 0.4 mg against 10% on placebo.Very common
ModerateShown to raise tiredness and nasal congestion in label trials, with stuffy or runny nose in 13% on tamsulosin 0.4 mg against 8% on placebo.Very common
ModerateThe label warns terazosin can cause fainting after the first dose or first few days, reported in about 1% of hypertension trial patients.Common
LimitedOne trial found doxazosin doubled heart failure against chlorthalidone in high blood pressure, 8.1% against 4.5% at 4 years, with more strokes. Heart attacks did not differ.Common
LimitedThe label warns tamsulosin, like other alpha-1 blockers, has rarely been linked to priapism, probably in fewer than 1 in 50,000 patients.Rare
StrongLinked to floppy iris syndrome during cataract surgery, most strongly for tamsulosin, at 31 times the odds in an updated meta-analysis. The labels warn of it.How often is not known
LimitedLinked to slightly more falls and fractures in the 90 days after older men started tamsulosin, alfuzosin or silodosin, with absolute increases under 0.2%.How often is not known
LimitedMixed results: one large cohort linked tamsulosin to 17% higher dementia risk, while a network meta-analysis of five studies found no link for alpha-blockers.How often is not known
LimitedThe labels warn that alpha-blockers with PDE5 inhibitors, other blood pressure drugs or nitrates can lower blood pressure further, with symptomatic hypotension possible.How often is not known
LimitedThe labels warn against tamsulosin, alfuzosin or silodosin with strong CYP3A4 inhibitors such as ketoconazole or clarithromycin, which raise drug levels. Ketoconazole nearly tripled tamsulosin exposure.How often is not known
LimitedThe alfuzosin label reports a small rise in the QT interval, larger at four times the usual dose, and advises caution in people with QT prolongation.How often is not known
LimitedSmall drops in hematocrit, hemoglobin, white cells and albumin were seen on terazosin in trials, which the label attributes to blood dilution. PSA did not change.How often is not known
LimitedSmall weight gains were seen in label trials, about 1 to 2 pounds on terazosin and 0.6 kg on doxazosin against small losses on placebo.How often is not known

What people take it for, and what was found

Shown to help7

StrongStudied in men

Urinary symptoms from an enlarged prostate

Shown to lower prostate symptom scores more than placebo in men with an enlarged prostate, by about 1 to 3 points, with small gains in urine flow.

Compared with placebo [1][2][3][4][5][6][7]

The numbers and sources

Effect: Against placebo, tamsulosin 0.4 mg lowered the Boyarsky symptom score 1.1 points more (95% CI 0.72 to 1.49, a 12% improvement) and 0.8 mg 1.6 points more, and raised peak urine flow 1.1 mL/sec more [1]. Silodosin lowered urologic symptom scores 2.65 points more than placebo (95% CI 2.08 to 3.23) [2]. A review of newer drugs found silodosin improved symptoms more than placebo, with moderate strength evidence [3]. In the label trials, the AUA symptom score fell 8.3 points on tamsulosin 0.4 mg and 5.5 on placebo over 13 weeks in one study [4], the IPSS fell 6.5 and 6.3 points on silodosin 8 mg against 3.6 and 3.4 on placebo over 12 weeks [5], and it fell 3.6, 6.9 and 6.5 points on alfuzosin 10 mg against 1.6, 4.9 and 4.6 on placebo in three trials [6]. Doxazosin raised maximum flow 2.3 to 3.3 mL/sec against 0.1 to 0.7 on placebo, and 34 to 42% gained 3 mL/sec or more against 13 to 17% [7].
Population: 4,122 men in 14 tamsulosin trials of 4 to 26 weeks, mean age 64 [1]; 1,968 men in 4 silodosin placebo trials [2]; over 9,000 men in 23 trials of newer drugs [3]; 1,486 men in two US tamsulosin trials [4]; 923 men in two silodosin trials [5]; about 1,150 men in three alfuzosin trials [6]; 609 men in three doxazosin trials [7].
Sources: [1], [2], [3], [4], [5], [6], [7]
Caveats: Trials were short, mostly 12 to 13 weeks, and no placebo trial in [1] ran past 13 weeks. The Cochrane review rated the silodosin symptom evidence low quality [2]. Label trials were run by the makers.

LimitedStudied in men

Long-term progression of an enlarged prostate

One trial found doxazosin cut overall BPH progression 39% against placebo over 4.5 years, but not urinary retention or the need for surgery. Doxazosin with finasteride cut it 66%.

Compared with placebo, finasteride, and doxazosin with finasteride [8]

The numbers and sources

Effect: Overall clinical progression, defined as a rise of at least 4 points in the AUA symptom score, acute urinary retention, incontinence, kidney insufficiency or recurrent urinary infection, fell 39% on doxazosin, 34% on finasteride and 66% on the combination against placebo. Acute urinary retention and the need for invasive therapy fell on the combination and on finasteride but not on doxazosin. Symptom scores improved in all three groups, most with the combination [8].
Population: 3,047 men with BPH followed a mean 4.5 years in a double-blind trial [8].
Sources: [8]
Caveats: One trial, and only doxazosin among the alpha-blockers. The abstract gives relative reductions without absolute rates.
Why limited: This rests on one trial, of 3,047 people. Strength counts independent studies that agree, so one trial is limited at any size.

StrongCommon

Passing a ureteral stone

Shown to raise stone passage, about 116 more per 1,000 in placebo-controlled trials, mainly for stones over 5 mm. Stones of 5 mm or less showed no clear benefit.

Compared with placebo or standard therapy [9]; placebo or control [10]

The numbers and sources

How common: Common: between 1 in 100 and 1 in 10 people.
Effect: Across all trials, stone clearance rose on an alpha-blocker (RR 1.45, 95% CI 1.36 to 1.55, low quality). In the higher-quality placebo-controlled trials the effect was smaller (RR 1.16, 95% CI 1.07 to 1.25), or 116 more clearances per 1,000. For stones 5 mm or smaller the RR was 1.06 (95% CI 0.98 to 1.15). Expulsion took 3.40 fewer days and hospital stays were fewer (RR 0.51) [9]. A second meta-analysis found more passage overall (RR 1.49, 95% CI 1.39 to 1.61), no clear benefit for smaller stones (RR 1.19, 95% CI 1.00 to 1.48) and 57% more passage for larger ones (RR 1.57, 95% CI 1.17 to 2.27), with less surgery (RR 0.44) [10].
Population: 10,509 adults in 67 trials, 5,787 of them in 15 placebo trials, with stones 1 cm or smaller [9]; 55 randomized trials [10].
Sources: [9], [10]
Caveats: Many trials were small and at risk of bias, and effects shrank in placebo-controlled trials [9]. Most trials used tamsulosin.

ModerateVery common

Stone fragments after shock wave lithotripsy

Shown to raise clearance of stone fragments after lithotripsy, from 69% to about 80%, in evidence a Cochrane review rated low certainty.

Compared with usual care alone or with placebo [13]

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: Stone fragment clearance rose on an alpha-blocker plus usual care (RR 1.16, 95% CI 1.09 to 1.23), from 69.3% to an estimated 80.4%, or 111 more per 1,000. Auxiliary treatments fell from 9.7% to 6.5% (RR 0.67, 95% CI 0.45 to 1.00), major adverse events fell from 25.8% to 15.5% (RR 0.60), and clearance came 3.74 days sooner [13].
Population: 4,793 adults in 40 trials, only 4 of them placebo-controlled, mean stone size 7.1 to 13.2 mm [13].
Sources: [13]
Caveats: Low certainty evidence with high heterogeneity (I² 78%) [13]. Most trials used tamsulosin.

ModerateStudied in menVery common

Urinating again after a catheter for urinary retention

Shown to help men urinate after catheter removal for acute urinary retention, 60% against 38% on placebo.

Compared with placebo [14]; no treatment [14]

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: 366 of 608 men (60.2%) on an alpha-blocker urinated without a new catheter, against 185 of 486 (38.1%) on placebo (RR 1.55, 95% CI 1.36 to 1.76). Repeat acute retention was less frequent (RR 0.69, 95% CI 0.60 to 0.79), significant for alfuzosin, tamsulosin and silodosin but not doxazosin. Adverse effects did not differ significantly (RR 1.19, 95% CI 0.75 to 1.89) [14].
Population: Men in 9 randomized trials, 8 against placebo and 1 against no treatment, with the catheter removed after 1 to 32 days of the drug [14].
Sources: [14]
Caveats: Moderate quality evidence, and trials defined success differently [14]. Later surgery was not reported.

Moderate

Blood pressure

Shown to lower blood pressure about 8/5 mm Hg more than placebo in high blood pressure, which the review authors called modest and likely an overestimate.

Compared with placebo [16][7]

The numbers and sources

Effect: Across four alpha-blockers, trough blood pressure fell an estimated 8/5 mm Hg more than on placebo, with no drug better or worse than another [16]. In pooled doxazosin label trials, doses of 1 to 16 mg lowered 24-hour blood pressure about 10/8 mm Hg standing and 9/5 mm Hg lying down against placebo [7].
Population: 1,175 adults with primary hypertension, baseline 155/101 mm Hg, in 10 trials of 3 to 12 weeks [16]; about 300 people per group in doxazosin trials [7].
Sources: [16], [7]
Caveats: Only 10 trials, and harms were poorly reported [16]. Tamsulosin, alfuzosin and silodosin are not indicated for blood pressure. For heart outcomes against a diuretic, see the heart failure block under Risks.

LimitedStudied in men

Parkinson disease

Limited evidence: two cohort studies linked terazosin, doxazosin or alfuzosin to lower Parkinson risk or fewer Parkinson events than tamsulosin, in men. No trial has tested this.

Compared with men taking tamsulosin [17][18]

The numbers and sources

Effect: Men starting terazosin, doxazosin or alfuzosin had a lower hazard of developing Parkinson disease than matched men starting tamsulosin, HR 0.88 (95% CI 0.81 to 0.98) in Danish registries and 0.63 (95% CI 0.58 to 0.69) in US claims, lower with longer use [17]. Among veterans already treated for Parkinson disease, Parkinson-related events were less frequent on these drugs than on tamsulosin (adjusted IRR 0.85, 95% CI 0.81 to 0.88) [18].
Population: 52,365 and 94,883 matched pairs of men [17]; 24,539 veterans with Parkinson disease taking an alpha-blocker [18].
Sources: [17], [18]
Caveats: Observational, and both studies compared against tamsulosin users rather than men taking no alpha-blocker. The idea rests on these drugs boosting a glycolysis enzyme, which tamsulosin does not.

Mixed results1

ModerateStudied in men

Chronic prostatitis and pelvic pain

Mixed results: alpha-blockers lowered chronic prostatitis symptom scores about 5 points more than placebo, but a Cochrane review rated the evidence very low certainty.

Compared with placebo [15]

The numbers and sources

Effect: Total NIH Chronic Prostatitis Symptom Index scores fell 5.01 points more than on placebo in the short term (95% CI 2.61 to 7.41, 18 studies) and 5.60 points more in the long term (95% CI 0.32 to 10.89, 4 studies). The review set its clinically important difference at a six-point drop or 25% of baseline. Sexual function, quality of life, anxiety and depression differed little [15].
Population: 2,061 men with chronic prostatitis or chronic pelvic pain syndrome in 24 trials [15].
Sources: [15]
Caveats: Very low quality evidence, and the review authors were uncertain of the effect [15].

Not shown to help2

ModerateStudied in men

Symptom relief, one alpha-blocker against another

Not shown to differ in symptom relief between silodosin and tamsulosin or naftopidil in men with an enlarged prostate. Alfuzosin did slightly better than silodosin in two small trials.

Compared with tamsulosin, naftopidil and alfuzosin [2]; other alpha-blockers and the saw palmetto extract Permixon [1]

The numbers and sources

Effect: Against tamsulosin, silodosin made little to no difference in urologic symptom scores (MD -0.04, 95% CI -1.31 to 1.24, 13 studies) or quality of life. Against naftopidil the difference was -0.85 points (95% CI -2.57 to 0.87). Against alfuzosin, symptom scores were 3.83 points higher on silodosin (95% CI 0.12 to 7.54) [2]. Tamsulosin 0.2 to 0.4 mg improved symptoms and flow about as much as other alpha-blockers [1].
Population: 2,129 men in 13 silodosin against tamsulosin trials, 763 against naftopidil and 155 against alfuzosin [2]; men in 14 tamsulosin trials [1].
Sources: [2], [1]
Caveats: Low-quality evidence for these comparisons [2]. Naftopidil is not sold in the US. The alfuzosin comparison rests on two small trials.

Moderate

Small ureteral stones in large placebo-controlled trials

Not shown to help small ureteral stones pass in two large trials, where tamsulosin and placebo gave the same rates, 81% against 80% and 50% against 47%.

Compared with placebo and nifedipine [11]; placebo [12]

The numbers and sources

Effect: In a UK trial, 81% on tamsulosin 400 µg, 80% on nifedipine and 80% on placebo needed no further intervention by 4 weeks (adjusted risk difference for tamsulosin 1.3%, 95% CI -5.7 to 8.3) [11]. In a US emergency department trial with a mean stone size of 3.8 mm, 50% passed the stone by day 28 on tamsulosin 0.4 mg and 47% on placebo (RR 1.05, 95.8% CI 0.87 to 1.27), and no secondary outcome differed [12].
Population: 1,136 adults aged 18 to 65 with a single ureteral stone of 10 mm or less at 24 UK hospitals [11]; 497 adults with stones under 9 mm at 6 US emergency departments [12].
Sources: [11], [12]
Caveats: Most stones in both trials were small, the group where the meta-analyses also found little effect [9][10]. The US trial excluded people lost to follow-up before stone passage [12].

Doses studied

Label trials used tamsulosin 0.4 mg or 0.8 mg once daily [4], silodosin 8 mg once daily [5], alfuzosin 10 mg extended-release once daily [6], doxazosin 1 to 8 mg in BPH and 1 to 16 mg in hypertension [7], and terazosin 1 to 20 mg once daily, starting at 1 mg [19]. The ureteral stone trials used tamsulosin 400 µg or 0.4 mg daily for up to 4 weeks [11][12]. In ALLHAT, doxazosin was given at 2 to 8 mg a day [20].

Risks

Reported risks13

ModerateVery common

Dizziness and low blood pressure on standing

Shown to raise dizziness and low blood pressure on standing in label trials, with dizziness in 15% on tamsulosin 0.4 mg against 10% on placebo.

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: Dizziness was reported by 14.9% on tamsulosin 0.4 mg, 17.1% on 0.8 mg and 10.1% on placebo, and at least one positive orthostatic test by 16%, 19% and 11% [4]. Dizziness was 15.6% on doxazosin against 9.0% on placebo in BPH trials and 19% against 9% in hypertension trials [7]. On terazosin it was 9.1% against 4.2%, and postural hypotension 3.9% against 0.8% [19]. On alfuzosin dizziness was 5.7% against 2.8% [6], and on silodosin 3.2% against 1.1%, with orthostatic hypotension 2.6% against 1.5% [5]. In chronic prostatitis trials, adverse events such as dizziness and postural hypotension were more frequent than on placebo (RR 1.60, 95% CI 1.09 to 2.34) [15].
Population: 1,487 men in two US tamsulosin trials [4]; 965 BPH and 675 hypertension patients in doxazosin trials [7]; 996 men in terazosin BPH trials [19]; 1,151 men in alfuzosin trials [6]; 923 men in silodosin trials [5]; 1,588 men in prostatitis trials [15].
Sources: [4], [7], [19], [6], [5], [15]
Caveats: Rates differ by drug and trial, and cross-trial comparisons between drugs are not reliable.

StrongStudied in menVery common

Ejaculation problems

Shown to raise ejaculation problems, most with silodosin, 28% against 1% on placebo, and on tamsulosin 8% at 0.4 mg. Doxazosin and terazosin were similar to placebo.

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: Ejaculatory dysfunction was more frequent on alpha-blockers than placebo (OR 5.88), on tamsulosin (OR 8.58) and on silodosin (OR 32.5), and less frequent on tamsulosin than on silodosin (OR 0.09). Doxazosin and terazosin were similar to placebo [21]. Silodosin raised sexual adverse events against placebo (RR 26.07, 180 more per 1,000) and against tamsulosin (RR 6.05, 141 more per 1,000) [2]. Retrograde ejaculation was 28.1% on silodosin and 0.9% on placebo, and 2.8% stopped silodosin for it [5]. Abnormal ejaculation was 8.4% on tamsulosin 0.4 mg, 18.1% on 0.8 mg and 0.2% on placebo [4].
Population: 23 randomized trials [21]; 1,968 men against placebo and 2,129 against tamsulosin [2]; 923 men [5]; 1,487 men [4].
Sources: [21], [2], [5], [4]
Caveats: The silodosin label states retrograde ejaculation reversed after stopping [5]. Ejaculatory problems were linked to greater symptom improvement in the meta-analysis [21].

ModerateVery common

Tiredness and stuffy nose

Shown to raise tiredness and nasal congestion in label trials, with stuffy or runny nose in 13% on tamsulosin 0.4 mg against 8% on placebo.

The numbers and sources

How common: Very common: more than 1 in 10 people.
Effect: Rhinitis was 13.1% on tamsulosin 0.4 mg, 17.9% on 0.8 mg and 8.3% on placebo, and asthenia 7.8% against 5.5% [4]. Fatigue was 8.0% on doxazosin against 1.7% on placebo in BPH trials [7]. Asthenia was 7.4% on terazosin against 3.3% [19]. Nasal congestion was 2.1% on silodosin against 0.2% [5].
Population: BPH label trials [4][7][19][5].
Sources: [4], [7], [19], [5]
Caveats: Label adverse reaction tables list events more frequent than placebo, so they are not a full list.

ModerateCommon

Fainting, most often after the first doses

The label warns terazosin can cause fainting after the first dose or first few days, reported in about 1% of hypertension trial patients.

The numbers and sources

How common: Common: between 1 in 100 and 1 in 10 people.
Effect: In trials of nearly 2,000 hypertensive patients, syncope was reported in about 1% on terazosin. In BPH trials it was 0.6% on terazosin against 0% on placebo. The risk was greatest in the first 7 days but continued at all times [19]. Syncope was 0.2% on tamsulosin 0.4 mg, 0.4% on 0.8 mg and 0.6% on placebo [4], and 0.2% on alfuzosin against 0% on placebo [6].
Population: Nearly 2,000 hypertensive patients and 996 men with BPH [19]; 1,487 men [4]; 1,151 men [6].
Sources: [19], [4], [6]
Caveats: Terazosin and doxazosin labels start at 1 mg because of this effect [19][7]. Tamsulosin did not differ from placebo.

LimitedCommon

Heart failure against a diuretic in high blood pressure

One trial found doxazosin doubled heart failure against chlorthalidone in high blood pressure, 8.1% against 4.5% at 4 years, with more strokes. Heart attacks did not differ.

The numbers and sources

How common: Common: between 1 in 100 and 1 in 10 people.
Effect: Fatal coronary disease or nonfatal heart attack did not differ (RR 1.03, 95% CI 0.90 to 1.17), nor did total mortality. Doxazosin raised stroke (RR 1.19, 95% CI 1.01 to 1.40), combined cardiovascular disease (4-year rates 25.45% against 21.76%) and heart failure (8.13% against 4.45%, RR 2.04, 95% CI 1.79 to 2.32). The doxazosin arm was stopped early [20].
Population: 24,335 adults aged 55 or older with hypertension and another heart risk factor, median follow-up 3.3 years [20].
Sources: [20]
Caveats: Compared with a diuretic, not placebo, so it shows doxazosin did less than chlorthalidone. One trial.
Why limited: This rests on one trial, of 24,335 people. Strength counts independent studies that agree, so one trial is limited at any size.

LimitedStudied in menRare

Priapism

The label warns tamsulosin, like other alpha-1 blockers, has rarely been linked to priapism, probably in fewer than 1 in 50,000 patients.

The numbers and sources

How common: Rare: fewer than 1 in 1,000 people.
Effect: The tamsulosin label puts priapism at probably less than 1 in 50,000 patients and states it can lead to permanent impotence if not treated [4]. One case was reported on silodosin in its 12-week trials [5].
Population: Postmarketing reports [4]; 466 men on silodosin [5].
Sources: [4], [5]
Caveats: Based on reports, not a trial rate.

StrongHow often is not known

Floppy iris during cataract surgery

Linked to floppy iris syndrome during cataract surgery, most strongly for tamsulosin, at 31 times the odds in an updated meta-analysis. The labels warn of it.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Tamsulosin carried the largest odds of intraoperative floppy iris syndrome, about 40-fold those of alfuzosin, the next highest. Alfuzosin and terazosin were also linked, and doxazosin reached significance in one analysis [22]. An updated meta-analysis found tamsulosin raised the odds 31-fold (OR 31.06, 95% CI 13.74 to 70.22) [23]. The tamsulosin label states the syndrome was seen in patients on or previously treated with alpha-1 blockers [4].
Population: 17 studies with 17,588 eyes [22]; 38 studies [23].
Sources: [22], [23], [4]
Caveats: Observational studies with wide intervals, and neither abstract gives the share of users affected.

LimitedStudied in menHow often is not known

Falls and fractures in older men

Linked to slightly more falls and fractures in the 90 days after older men started tamsulosin, alfuzosin or silodosin, with absolute increases under 0.2%.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Men starting a prostate-selective alpha-blocker had more falls (OR 1.14, 95% CI 1.07 to 1.21, absolute increase 0.17%) and fractures (OR 1.16, 95% CI 1.04 to 1.29, absolute increase 0.06%) than matched men who did not, and more hypotension (OR 1.80) and head trauma (OR 1.15) [24].
Population: 147,084 men aged 66 or older in Ontario and as many matched men, 84% on tamsulosin [24].
Sources: [24]
Caveats: Observational, with possible unmeasured confounding such as mobility. The authors note the absolute risks are probably underestimates [24].

LimitedHow often is not known

Interaction with blood pressure drugs, nitrates and erectile dysfunction drugs

The labels warn that alpha-blockers with PDE5 inhibitors, other blood pressure drugs or nitrates can lower blood pressure further, with symptomatic hypotension possible.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: The doxazosin label states that taking it with a PDE5 inhibitor can add to blood pressure lowering and cause symptomatic hypotension [7]. In 24 healthy men, silodosin with sildenafil 100 mg or tadalafil 20 mg produced more positive orthostatic tests than silodosin alone, with no symptomatic events [5]. The alfuzosin label warns of more hypotension and fainting with blood pressure drugs and nitrates [6]. The tamsulosin label advises caution with PDE5 inhibitors [4].
Population: Label statements, and 24 men aged 45 to 78 in one study [5].
Sources: [7], [5], [6], [4]
Caveats: Mostly label warnings rather than measured rates.

LimitedHow often is not known

Interaction with strong CYP3A4 inhibitors

The labels warn against tamsulosin, alfuzosin or silodosin with strong CYP3A4 inhibitors such as ketoconazole or clarithromycin, which raise drug levels. Ketoconazole nearly tripled tamsulosin exposure.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Ketoconazole raised tamsulosin peak levels 2.2-fold and exposure 2.8-fold, and the label advises against combining tamsulosin 0.4 mg with strong CYP3A4 inhibitors [4]. Alfuzosin is contraindicated with ketoconazole, itraconazole and ritonavir [6]. Silodosin is contraindicated with strong CYP3A4 inhibitors including ketoconazole, clarithromycin, itraconazole and ritonavir [5].
Population: Pharmacokinetic studies in the labels [4][6][5].
Sources: [4], [6], [5]
Caveats: Drug level studies, not outcome trials.

LimitedHow often is not known

QT prolongation with alfuzosin

The alfuzosin label reports a small rise in the QT interval, larger at four times the usual dose, and advises caution in people with QT prolongation.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: In a postmarketing study, alfuzosin 10 mg raised placebo-subtracted QTcF by 1.9 msec, and by 5.9 msec when given with another drug of similar QT effect, against 10.2 msec for moxifloxacin. The QT effect appeared greater at 40 mg than 10 mg [6].
Population: 45 healthy men aged 19 to 45 in a crossover study, and a separate postmarketing QT study [6].
Sources: [6]
Caveats: The label calls the clinical impact of these changes unknown [6].

LimitedHow often is not known

Small drops in blood counts and albumin

Small drops in hematocrit, hemoglobin, white cells and albumin were seen on terazosin in trials, which the label attributes to blood dilution. PSA did not change.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Small but statistically significant decreases in hematocrit, hemoglobin, white blood cells, total protein and albumin were seen in controlled trials. Treatment for up to 24 months had no significant effect on PSA [19].
Population: People in terazosin controlled trials [19].
Sources: [19]
Caveats: The label gives no size for the drops.

LimitedHow often is not known

Weight gain

Small weight gains were seen in label trials, about 1 to 2 pounds on terazosin and 0.6 kg on doxazosin against small losses on placebo.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Men and women on terazosin gained a mean of 1.7 and 2.2 pounds against losses of 0.2 and 1.2 pounds on placebo [19]. In doxazosin hypertension trials, people gained a mean of 0.6 kg against a 0.1 kg loss on placebo [7].
Population: Placebo-controlled terazosin monotherapy trials [19]; about 300 hypertensive patients per group [7].
Sources: [19], [7]
Caveats: Possibly related to fluid. Neither label separates water from body tissue.

Mixed results1

LimitedHow often is not known

Dementia

Mixed results: one large cohort linked tamsulosin to 17% higher dementia risk, while a network meta-analysis of five studies found no link for alpha-blockers.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: In Medicare data, dementia incidence was 31.3 per 1,000 person-years on tamsulosin against 25.9 with no BPH drug (HR 1.17, 95% CI 1.14 to 1.21), and higher than on doxazosin, terazosin or alfuzosin [25]. A Bayesian network meta-analysis found neither alpha-blockers nor 5-alpha reductase inhibitors significantly linked to dementia against no treatment [26].
Population: 253,136 men aged 65 or older with BPH on tamsulosin, with matched comparison groups, median follow-up 19.8 months [25]; 3,650,434 patients in 5 studies [26].
Sources: [25], [26]
Caveats: Observational studies, with short follow-up in [25]. Dementia can take years to be diagnosed, so early diagnoses after starting a drug are hard to attribute.

Possible, not studied in people1

Untested

Use in pregnancy

Not studied in people. Animal studies of doxazosin found no birth defects at usual multiples of human exposure, with lower fetal survival in rabbits at the highest dose.

No study in people. This rests on animal studies.

The numbers and sources

Effect: The doxazosin label states that limited data in pregnant women are not enough to inform the risk of birth defects or miscarriage. In rats and rabbits given doxazosin during organogenesis at 4 to 10 times human exposure, no adverse developmental effects were seen, and 82 mg/kg a day reduced fetal survival in rabbits [7].
Population: Rats and rabbits [7].
Sources: [7]
Caveats: Animal data only. Tamsulosin, alfuzosin and silodosin are labeled for men with BPH.

Claims tested and not found

That tamsulosin helps small ureteral stones pass. In two large placebo-controlled trials, stone passage or freedom from intervention did not differ from placebo [11][12].
That an alpha-blocker alone prevents urinary retention or prostate surgery over years. In 3,047 men followed 4.5 years, doxazosin did not lower acute urinary retention or invasive therapy, while finasteride and the combination did [8].
That the more selective silodosin relieves prostate symptoms more than tamsulosin. Symptom scores did not differ between them across 13 trials (MD -0.04) [2].
That alpha-blockers lower heart events when used for blood pressure. Against chlorthalidone, doxazosin did not lower coronary events and raised heart failure and stroke [20].

Finasteride Saw palmetto

Sources

Wilt TJ, MacDonald R, Rutks I. Tamsulosin for benign prostatic hyperplasia. Cochrane Database of Systematic Reviews. 2002. https://doi.org/10.1002/14651858.CD002081
Jung JH, Kim J, MacDonald R, et al. Silodosin for the treatment of lower urinary tract symptoms in men with benign prostatic hyperplasia. Cochrane Database of Systematic Reviews. 2017. https://doi.org/10.1002/14651858.CD012615.pub2
MacDonald R, Brasure M, Dahm P, et al. Efficacy of newer medications for lower urinary tract symptoms attributed to benign prostatic hyperplasia: a systematic review. The Aging Male. 2019. https://doi.org/10.1080/13685538.2018.1434503
U.S. Food and Drug Administration. Tamsulosin hydrochloride capsules, prescribing information. 2025. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=fb120098-b007-4a33-80b8-b7279c7668ee
U.S. Food and Drug Administration. Silodosin capsules, prescribing information. 2026. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=de619e27-9384-4b86-abdc-de0557cd39e8
U.S. Food and Drug Administration. UROXATRAL (alfuzosin HCl) extended-release tablets, prescribing information. 2025. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9fc7f119-f36b-44cf-945d-940160f3afe3
U.S. Food and Drug Administration. CARDURA (doxazosin) tablets, prescribing information. 2026. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5e1f5e49-2da1-43ab-9795-228a8bcc5a82
McConnell JD, Roehrborn CG, Bautista OM, et al. The long-term effect of doxazosin, finasteride, and combination therapy on the clinical progression of benign prostatic hyperplasia. New England Journal of Medicine. 2003. https://doi.org/10.1056/NEJMoa030656
Campschroer T, Zhu X, Vernooij RW, et al. Alpha-blockers as medical expulsive therapy for ureteral stones. Cochrane Database of Systematic Reviews. 2018. https://doi.org/10.1002/14651858.CD008509.pub3
Hollingsworth JM, Canales BK, Rogers MAM, et al. Alpha blockers for treatment of ureteric stones: systematic review and meta-analysis. BMJ. 2016. https://doi.org/10.1136/bmj.i6112
Pickard R, Starr K, MacLennan G, et al. Medical expulsive therapy in adults with ureteric colic: a multicentre, randomised, placebo-controlled trial. The Lancet. 2015. https://doi.org/10.1016/S0140-6736(15)60933-3
Meltzer AC, Burrows PK, Wolfson AB, et al. Effect of Tamsulosin on Passage of Symptomatic Ureteral Stones: A Randomized Clinical Trial. JAMA Internal Medicine. 2018. https://doi.org/10.1001/jamainternmed.2018.2259
Oestreich MC, Vernooij RW, Sathianathen NJ, et al. Alpha-blockers after shock wave lithotripsy for renal or ureteral stones in adults. Cochrane Database of Systematic Reviews. 2020. https://doi.org/10.1002/14651858.CD013393.pub2
Fisher E, Subramonian K, Omar MI. The role of alpha blockers prior to removal of urethral catheter for acute urinary retention in men. Cochrane Database of Systematic Reviews. 2014. https://doi.org/10.1002/14651858.CD006744.pub3
Franco JV, Turk T, Jung JH, et al. Pharmacological interventions for treating chronic prostatitis/chronic pelvic pain syndrome. Cochrane Database of Systematic Reviews. 2019. https://doi.org/10.1002/14651858.CD012552.pub2
Heran BS, Galm BP, Wright JM. Blood pressure lowering efficacy of alpha blockers for primary hypertension. Cochrane Database of Systematic Reviews. 2012. https://doi.org/10.1002/14651858.CD004643.pub3
Simmering JE, Welsh MJ, Liu L, et al. Association of Glycolysis-Enhancing α-1 Blockers With Risk of Developing Parkinson Disease. JAMA Neurology. 2021. https://doi.org/10.1001/jamaneurol.2020.5157
Opheim KM, Uc EY, Cantrell MA, et al. The impact of alpha-1-adrenergic receptor antagonists on the progression of Parkinson disease. Journal of the American Pharmacists Association. 2024. https://doi.org/10.1016/j.japh.2023.12.008
U.S. Food and Drug Administration. Terazosin hydrochloride capsules, prescribing information. 2026. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=5a95be60-b242-9183-e063-6394a90a89e6
ALLHAT Collaborative Research Group. Major cardiovascular events in hypertensive patients randomized to doxazosin vs chlorthalidone: the antihypertensive and lipid-lowering treatment to prevent heart attack trial (ALLHAT). JAMA. 2000. https://doi.org/10.1001/jama.283.15.1967
Gacci M, Ficarra V, Sebastianelli A, et al. Impact of medical treatments for male lower urinary tract symptoms due to benign prostatic hyperplasia on ejaculatory function: a systematic review and meta-analysis. The Journal of Sexual Medicine. 2014. https://doi.org/10.1111/jsm.12525
Chatziralli IP, Sergentanis TN. Risk factors for intraoperative floppy iris syndrome: a meta-analysis. Ophthalmology. 2011. https://doi.org/10.1016/j.ophtha.2010.08.039
Christou CD, Esagian SM, Ziakas N, et al. Factors predisposing to intraoperative floppy-iris syndrome: An up-to-date meta-analysis. Journal of Cataract and Refractive Surgery. 2022. https://doi.org/10.1097/j.jcrs.0000000000001017
Welk B, McArthur E, Fraser LA, et al. The risk of fall and fracture with the initiation of a prostate-selective α antagonist: a population based cohort study. BMJ. 2015. https://doi.org/10.1136/bmj.h5398
Duan Y, Grady JJ, Albertsen PC, Wu ZH. Tamsulosin and the risk of dementia in older men with benign prostatic hyperplasia. Pharmacoepidemiology and Drug Safety. 2018. https://doi.org/10.1002/pds.4361
Niaga KJK, Rinaldi FX, Nathania N, et al. Do Alpha-Blockers and 5-Alpha Reductase Inhibitors Increase Dementia Risk? A Network Meta-analysis. International Neurourology Journal. 2025. https://doi.org/10.5213/inj.2550174.087

Everything in the library

Shown to help7

Reported risks14

What people take it for, and what was found

Shown to help7

Mixed results1

Not shown to help2

Doses studied

Risks

Reported risks13

Mixed results1

Possible, not studied in people1

Claims tested and not found

Related

Sources