What does the research show about citrulline?

Citrulline

Meta-analyses find a single pre-workout dose of citrulline or citrulline malate gives a small gain in strength and power tasks (SMD 0.20) and about 6% more reps to failure. Aerobic performance did not change. In older adults, pooled trials found systolic pressure 4 mmHg lower, and an earlier, smaller analysis found no change. Harms are barely studied.

Add to Bio HackChecked 2026-11-09

Status: Dietary supplement in the US.
Also called: L-citrulline, citrulline malate, CitMal, CM, watermelon extract, nitric oxide booster, pump supplement
Taken for: muscle pump, more reps, strength, power, endurance, less soreness, blood flow, nitric oxide, blood pressure, erections

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 help3

ModerateShown to slightly improve resistance sets and short sprints in mostly strength-trained adults, with about 6% more repetitions to failure on 6 to 8 g.
ModerateShown to raise flow-mediated dilation, a measure of artery widening, in middle-aged and older adults. Arterial stiffness did not change.
LimitedOne small trial found erection hardness improved in 50% of men with mild erectile dysfunction on 1.5 g a day, against 8.3% on placebo.

Reported risks0

No risks sourced yet.

What people take it for, and what was found

Shown to help3

Moderate

Strength and power during high-intensity sets

Shown to slightly improve resistance sets and short sprints in mostly strength-trained adults, with about 6% more repetitions to failure on 6 to 8 g.

The numbers and sources

Effect: Across 12 studies (13 samples, 198 participants) using at least 3 g taken at least 30 minutes before testing, citrulline improved resistance sets and sprints of 30 seconds or less by SMD 0.20 (95% CI 0.01 to 0.39), with no heterogeneity (I² 0%) [1]. In 8 studies (137 participants), 6 to 8 g of citrulline malate 40 to 60 minutes before training added 3 ± 5 repetitions to failure, 6.4% over placebo (SMD 0.196). Lower body trended up (SMD 0.27, p = 0.051) and upper body did not change (SMD 0.16) [2].
Population: Healthy, mostly strength-trained adults [1]; 101 trained men, 26 trained women and 9 untrained men in [2].
Sources: [1], [2]
Caveats: Every individual study's confidence interval crossed zero; only the pooled estimate did not [1].

Moderate

Blood flow and blood vessel function

Shown to raise flow-mediated dilation, a measure of artery widening, in middle-aged and older adults. Arterial stiffness did not change.

The numbers and sources

Effect: In 8 RCTs (176 participants), L-citrulline raised flow-mediated dilation, a measure of artery widening (mean difference 1.81, 95% CI 0.76 to 2.85), and did not change pulse wave velocity, a measure of arterial stiffness (-0.14, 95% CI -0.45 to 0.17). Watermelon changed neither [12]. In the postmenopausal review, 2 of 4 trials found flow-mediated dilation improved, and arterial stiffness findings were mixed [9].
Population: Middle-aged and older adults [12]; postmenopausal women [9].
Sources: [12], [9]
Caveats: Small trials. These are measures of vessel function, not heart attacks or strokes.

LimitedStudied in men

Erection hardness

One small trial found erection hardness improved in 50% of men with mild erectile dysfunction on 1.5 g a day, against 8.3% on placebo.

The numbers and sources

Effect: In 24 men (mean age 56.5) with mild erectile dysfunction, 1.5 g a day for a month moved erection hardness from score 3 to 4 in 12 men (50%), against 2 men (8.3%) during a month of placebo. Intercourse rose from 1.53 to 2.3 times a month [13].
Population: 24 men with mild erectile dysfunction [13].
Sources: [13]
Caveats: Single-blind, not randomized in order, one month per phase, 24 men. No meta-analysis located.

Mixed results2

Limited

Muscle soreness and perceived effort

Limited evidence: perceived effort and soreness at 24 hours fell in one review, while a larger review found no effect on perceived effort.

The numbers and sources

Effect: Across 13 articles (206 participants), citrulline lowered rating of perceived exertion (7 studies, p = 0.03) and muscle soreness at 24 hours (7 studies, p = 0.04), but not at 48 hours (p = 0.25) or 72 hours (p = 0.62). Blood lactate did not change (8 studies, p = 0.17) [4].
Population: Healthy adults; 8 g citrulline malate was the most common dose [4].
Sources: [4]
Caveats: The abstract reports p-values without effect sizes. The results sentence groups soreness at 24 and 48 hours as reduced, but the 48-hour p-value is 0.25 [4]. A 2026 three-level meta-analysis of citrulline malate (30 RCTs, 644 participants) found no significant pooled effect on perceived exertion, so sources disagree on effort [5].

Moderate

Blood pressure

Mixed results: reviews in older adults and during cold exposure found systolic pressure about 4 to 9 mmHg lower, while an earlier, smaller analysis found no change.

The numbers and sources

Effect: In 15 RCTs (24 datasets, 415 participants) of L-citrulline or watermelon in middle-aged and older adults, systolic pressure fell 4.02 mmHg (95% CI -6.54 to -1.50) and diastolic 2.54 mmHg (95% CI -4.27 to -0.81). L-citrulline combined with L-arginine lowered systolic pressure 10.44 mmHg (95% CI -13.57 to -7.31) [7]. In 6 RCTs (162 participants) measuring blood pressure during cold exposure, systolic pressure was 9.28 mmHg lower (95% CI -10.66 to -7.90) and diastolic 5.33 mmHg lower (95% CI -9.38 to -1.27) with L-citrulline [8]. In a systematic review of 12 RCTs in 360 postmenopausal women, most of the 7 trials that measured blood pressure reported lower systolic and mean arterial pressure [9]. An earlier analysis of 5 interventions found no change in brachial systolic (0.28 mmHg, 95% CI -2.87 to 2.31), diastolic (-1.56 mmHg, 95% CI -4.32 to 1.20) or aortic pressure [10]. A 2018 meta-analysis reporting a 7.54 mmHg systolic drop across 15 trials has been retracted by its journal [11].
Population: Middle-aged and older adults [7]; adults under cold exposure [8]; postmenopausal women aged 50 to 75 in 4 to 8 week US trials [9]; adults, with body weight a source of heterogeneity [10].
Sources: [7], [8], [9], [10], [11]
Caveats: Sources disagree. The reductions come from analyses of older adults and of cold exposure, and the earlier, smaller analysis found no change [10]. The older-adult analysis pooled L-citrulline, watermelon and citrulline with arginine [7]. Two of the analyses come from one author group [7][8]. The postmenopausal review did not pool results [9]. The retracted paper [11] is listed so that readers who meet its numbers elsewhere know its status.

Not shown to help2

Limited

Maximal strength

Limited evidence: 4 studies found no effect of citrulline malate on maximal muscle strength in resistance-trained adults.

The numbers and sources

Effect: In 4 studies (69 citrulline malate and 69 placebo assessments), there was no overall effect on muscle strength (SMD 0.13, 95% CI -0.21 to 0.46), for lower (0.06) or upper (0.17) limbs [3].
Population: Resistance-trained adults [3].
Sources: [3]
Caveats: Four studies. This and the repetition analysis [2] measure different things: maximal force versus reps to failure.

Moderate

Aerobic endurance

Not shown to change aerobic performance, perceived effort or lactate in healthy adults across 10 trials.

The numbers and sources

Effect: Across 10 placebo-controlled studies, citrulline did not change aerobic performance (SMD 0.15, 95% CI -0.02 to 0.32), perceived exertion (-0.03), oxygen uptake kinetics (0.01) or lactate (0.25, 95% CI -0.10 to 0.59) [6].
Population: Healthy adults in aerobic tests [6].
Sources: [6]
Caveats: The authors note chronic protocols showed a positive tendency that has not been tested in enough trials [6].

Doses studied

Strength and power trials pooled in meta-analysis used at least 3 g, taken at least 30 minutes before testing [1]. Repetition trials used 6 to 8 g of citrulline malate 40 to 60 minutes before training [2]. The most frequent dose in soreness trials was 8 g of citrulline malate [4]. The erectile function trial used 1.5 g a day of L-citrulline for one month [13]. Citrulline malate is citrulline bound to malic acid, so a gram of citrulline malate contains less than a gram of citrulline; trials report the form used.

Risks

Checked, no increase found1

Limited

Adverse effects in trials

Limited evidence: no adverse events related to citrulline were reported in small trials of up to 8 weeks.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: The erectile function trial reported no adverse events in 24 men over one month [13]. A systematic review of 12 RCTs in 360 postmenopausal women found no adverse effects related to citrulline reported in any trial [9]. No pooled analysis of adverse effect rates was located.
Population: Small, short trials [13]; trials of 4 to 8 weeks [9].
Sources: [13], [9]
Caveats: Searched Europe PMC titles for citrulline with safety, adverse, side effects, toxicity and tolerability terms. Performance meta-analyses [1][2][3] do not report adverse event data in their abstracts.

Possible, not studied in people1

UntestedHow often is not known

Combining with blood pressure or erectile dysfunction medication

Not studied in people. Predicted, not observed: citrulline lowered blood pressure in trials, and the sildenafil label warns of added blood pressure drops with nitrates and blood pressure drugs.

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

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: Citrulline lowered systolic pressure by 4.02 mmHg in pooled trials in middle-aged and older adults [7]. The sildenafil label lists nitrates as a contraindication because sildenafil potentiates their blood pressure lowering effect, and reports a further fall of 8 mmHg systolic and 7 mmHg diastolic when sildenafil was taken with amlodipine by people with high blood pressure [14]. In dogs, injected citrulline given with oral sildenafil raised nitric oxide levels more than saline or citrulline alone, and raised penile and testicular artery blood flow within 1 to 8 hours. The study had no sildenafil-only group [15]. No study measured blood pressure in people taking citrulline with any of these drugs.
Population: Adults in blood pressure trials [7]. Label data from people taking sildenafil [14]. 18 German Shepherd dogs [15].
Sources: [7], [14], [15]
Caveats: The concern is inferred from each part acting on the same nitric oxide pathway. The dog study gave citrulline by injection and did not report blood pressure [15].

Claims tested and not found

That citrulline improves endurance. Aerobic performance did not differ from placebo across 10 studies [6].
That citrulline raises maximal strength. One-rep and maximal force measures did not change across 4 trials [3].

Sources

Trexler ET, Persky AM, Ryan ED, et al. Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis. Sports Medicine. 2019. https://doi.org/10.1007/s40279-019-01091-z
Vårvik FT, Bjørnsen T, Gonzalez AM. Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-Analysis. International Journal of Sport Nutrition and Exercise Metabolism. 2021. https://doi.org/10.1123/ijsnem.2020-0295
Aguiar AF, Casonatto J. Effects of Citrulline Malate Supplementation on Muscle Strength in Resistance-Trained Adults: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Journal of Dietary Supplements. 2021. https://doi.org/10.1080/19390211.2021.1939473
Rhim HC, Kim SJ, Park J, et al. Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysis. Journal of Sport and Health Science. 2020. https://doi.org/10.1016/j.jshs.2020.02.003
Wang X, Fan X, Chang J, et al. Effects of Citrulline Malate Supplementation on Exercise Performance: A Systematic Review and Three-Level Meta-Analysis. Nutrients. 2026. https://doi.org/10.3390/nu18121881
Viribay A, Fernández-Landa J, Castañeda-Babarro A, et al. Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-Analysis. Nutrients. 2022. https://doi.org/10.3390/nu14173479
Luo P, Chen J, Liu K, et al. Does l-citrulline supplementation and watermelon intake reduce blood pressure in middle-aged and older adults? A systematic review and meta-analysis of randomized controlled trials. Clinical Nutrition ESPEN. 2025. https://doi.org/10.1016/j.clnesp.2025.07.1130
Luo P, Chen J, Liu K, et al. Effect of L-Citrulline Intake on Blood Pressure in Cold Environments: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Food Science & Nutrition. 2026. https://doi.org/10.1002/fsn3.71603
Bahari H, Ramezani E, Malekahmadi M. Citrulline supplementation in postmenopausal women: a systematic review of vascular, muscular, and metabolic effects. BMC Women's Health. 2026. https://doi.org/10.1186/s12905-026-04277-6
Mirenayat MS, Moradi S, Mohammadi H, et al. Effect of L-Citrulline Supplementation on Blood Pressure: a Systematic Review and Meta-Analysis of Clinical Trials. Current Hypertension Reports. 2018. https://doi.org/10.1007/s11906-018-0898-3
Mahboobi S, Tsang C, Rezaei S, et al. RETRACTED ARTICLE: Effect of L-citrulline supplementation on blood pressure: a systematic review and meta-analysis of randomized controlled trials. Journal of Human Hypertension. 2018. https://doi.org/10.1038/s41371-018-0108-4
Luo P, Li Z, Liu K, et al. Effects of L-citrulline supplementation and watermelon intake on arterial stiffness and endothelial function in middle-aged and older adults: a systematic review and meta-analysis of randomized controlled trials. Frontiers in Nutrition. 2025. https://doi.org/10.3389/fnut.2025.1632952
Cormio L, De Siati M, Lorusso F, et al. Oral L-Citrulline Supplementation Improves Erection Hardness in Men With Mild Erectile Dysfunction. Urology. 2011. https://doi.org/10.1016/j.urology.2010.08.028
U.S. Food and Drug Administration. VIAGRA (sildenafil citrate) tablets, prescribing information. 2023. DailyMed. https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=d905dc8d-917f-4ea3-a4ee-a1ecf6967d4e
Abdelnaby EA. The impacts of L-citrulline and sildenafil on penile and testicular vascular perfusion pattern, advanced testicular analysis, steroids, and semen picture in normospermic dogs. Veterinary Research Communications. 2025. https://doi.org/10.1007/s11259-025-10965-9

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