Research review
L-citrulline: what the research does and doesn't show
L-citrulline's exercise-performance evidence is mixed — a small pooled benefit in one meta-analysis, no benefit at all in a separate well-controlled trial. Blood-pressure reductions are real but narrow, limited to people who already have elevated readings, and a controlled trial links watermelon's citrulline to triggering migraine in some people already diagnosed with it.
The evidence doesn't support L-citrulline as a treatment for any diagnosed condition, and it doesn't reliably improve exercise performance in every study that's tested it — one recent trial found no benefit at all. What's actually been found across the research: a small, inconsistent exercise-performance effect, blood-pressure reductions specific to people who already have elevated blood pressure, and a mechanism that, in at least one documented case, plausibly worked against a specific group of people rather than for them.
What the evidence doesn't support
It doesn't support L-citrulline as a treatment, cure or prevention for any diagnosed disease, including erectile dysfunction, hypertension, or cardiovascular disease. It doesn't support a guaranteed exercise-performance benefit — while a 2019 meta-analysis found a small pooled benefit across 12 studies, a 2024 trial testing a single dose found no improvement in strength, jump performance or strength-endurance at all. It doesn't support a blood-pressure effect in people whose blood pressure is already normal. And it doesn't support the idea that citrulline is risk-free for everyone: in people already prone to migraine, the same nitric-oxide pathway citrulline raises has been linked to triggering an attack after eating a citrulline-rich food.
What the trials found
A 2019 systematic review and meta-analysis pooled 12 studies (198 participants) testing a single citrulline dose — at least 3 g, given 30-plus minutes before high-intensity strength or power exercise — against placebo. The pooled result favored citrulline by a small, statistically significant margin (standardized mean difference 0.20, 95% CI 0.01-0.39, p=0.036), though every individual study's own confidence interval still crossed the line of no effect.
Against that, a 2024 randomized, double-blind, placebo-controlled crossover trial gave 43 young, trained adults a single 5.3 g dose of plain L-citrulline, the same amount combined with malic acid as citrulline malate, or placebo, 45 minutes before testing. Neither citrulline form improved maximal strength, jump performance, or strength-endurance in the squat or bench press, compared with placebo — a clean null result from a well-controlled trial, sitting alongside the smaller positive pooled effect above.
A 2010 randomized, crossover trial gave 41 men a single 8 g dose of citrulline malate before a bench-press session. Repetitions completed increased significantly from the third set onward, reaching 53% more than placebo by the final set, and next-day muscle soreness was about 40% lower. About 15% of participants reported stomach discomfort — the clearest side effect documented in any trial reviewed across this site's L-citrulline coverage.
A 2025 meta-analysis pooling 15 randomized trials (415 middle-aged and older adults) found L-citrulline supplementation and watermelon intake lowered systolic blood pressure by about 4 mmHg and diastolic by about 2.5 mmHg on average, specifically in adults who already had elevated blood pressure. See does L-citrulline help with blood pressure? for the full picture, including what it doesn't show.
A 2023 controlled trial gave 38 people with migraine without aura and 38 headache-free controls a standardized portion of watermelon — a food naturally high in citrulline — and monitored them for headache onset. Watermelon triggered a headache within about 2 hours in 23.7% of the migraine group and none of the controls (p=0.002), while a nitric-oxide-pathway blood marker rose by a similar amount in both groups. It's a study of whole watermelon in people already diagnosed with migraine, not an isolated citrulline supplement in a general population — but the shared nitric-oxide mechanism is the plausible link, and it's the one documented case in this research where citrulline's core mechanism worked against a specific group rather than for them.
Questions people ask
Can L-citrulline cause headaches?
No trial reports headache as a direct side effect of an isolated L-citrulline supplement. The closest evidence is indirect: a 2023 controlled trial found watermelon — a citrulline-rich food — triggered a headache in about 1 in 4 people already diagnosed with migraine, through the same nitric-oxide pathway citrulline raises, while triggering none in headache-free people. That's a reason people with diagnosed migraine might want to be cautious, not evidence that citrulline supplements cause headaches generally.
How does L-citrulline help with post-workout recovery?
The clearest recovery-adjacent finding is from a 2010 trial: a single 8 g dose of citrulline malate before a bench-press session reduced next-day and two-day muscle soreness by about 40%, compared with placebo. That's one trial, using the malate form, measuring soreness specifically — not a broader recovery outcome like return to full training capacity.
Is L-citrulline good for you?
It depends entirely on which specific use you mean. The exercise-performance evidence is mixed — a small pooled benefit in one meta-analysis, no benefit at all in a separate well-controlled trial. The blood-pressure evidence is real but narrow, limited to people who already have elevated readings. Nothing here makes citrulline a general-purpose health supplement with a single yes-or-no answer.
What is L-citrulline good for?
Across the trials on this site: a small, inconsistent improvement in high-intensity exercise performance and muscular endurance; a blood-pressure reduction specific to people with already-elevated blood pressure; and improved erection hardness in men with mild erectile dysfunction in one small trial. See L-citrulline benefits: what the research does and doesn't show for each finding's real limits.
Does L-citrulline actually work?
For some specific outcomes, in some trials, yes — with effect sizes ranging from small to null depending on the study. It isn't a supplement where "does it work" has one answer; it depends on which outcome, which dose and form, and which specific trial you're asking about.
When to talk to a doctor
L-citrulline is not a treatment for any diagnosed condition, and nothing above should stand in for a doctor's evaluation or treatment of one. If you have diagnosed hypertension, cardiovascular disease, erectile dysfunction, diagnosed migraine, or reduced kidney function, or take a regular prescription medication, talk to a doctor before starting L-citrulline.
Related reading: what is L-citrulline?, L-citrulline benefits: what the research does and doesn't show, and L-citrulline side effects.
Sources
- Acute Effects of Citrulline Supplementation on High-Intensity Strength and Power Performance: A Systematic Review and Meta-Analysis A 2019 meta-analysis pooling 12 studies (198 people) found a small but statistically significant benefit of a single citrulline dose (at least 3 g, taken 30+ minutes before exercise) on high-intensity strength and power performance, though every individual study's own result could still have been due to chance.
- Malate or Not? Acute Effects of L-Citrulline Versus Citrulline Malate on Neuromuscular Performance in Young, Trained Adults: A Randomized, Double-Blind, Placebo-Controlled Crossover Trial A 2024 randomized, double-blind, placebo-controlled crossover trial in 43 young, trained men and women found that neither a single 5.3 g dose of plain L-citrulline nor the same amount combined with malic acid as citrulline malate improved maximal strength, jump performance, or strength-endurance in the squat or bench press, compared with placebo.
- Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness A 2010 crossover trial in 41 men found a single 8 g dose of citrulline malate before a bench-press session increased the number of repetitions completed as the sets went on, and reduced next-day and two-day muscle soreness by about 40%, compared with placebo; about 15% of participants reported stomach discomfort.
- 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 A 2025 meta-analysis pooling 15 randomized trials (415 middle-aged and older adults) found that L-citrulline supplementation and watermelon intake lowered systolic blood pressure by about 4 mmHg and diastolic blood pressure by about 2.5 mmHg on average, compared with placebo, with a larger reduction in the subset of trials that combined citrulline with L-arginine.
- Migraine Attacks Triggered by Ingestion of Watermelon A 2023 controlled trial found that eating watermelon — a food naturally high in citrulline — triggered a migraine attack within about 2 hours in roughly 1 in 4 people with a migraine diagnosis, and in none of the headache-free control group, while raising a nitric-oxide-pathway blood marker similarly in both groups; the study is about whole watermelon in people already diagnosed with migraine, not an isolated citrulline supplement in a general population.
- Oral L-citrulline supplementation improves erection hardness in men with mild erectile dysfunction A 2011 single-blind trial in 24 men with mild erectile dysfunction found that 1.5 g/day of L-citrulline for a month improved erection hardness in half the men, versus about 8% during a placebo month, with no adverse events reported — the study's own authors describe it as less effective than standard PDE-5 inhibitor medication.
*These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.