Printed from https://bottledhope.co/supplements/l-citrulline/. Last reviewed 2026-09-26. Check the site for the latest version.
L-citrulline
An amino acid the body makes and watermelon contains. A 2026 review describes citrulline malate as a supplement marketed to aid exercise performance.
Explained simply · Last reviewed
What it is
L-citrulline is an amino acid that the body makes and that some foods contain. The US Office of Dietary Supplements (ODS), part of the National Institutes of Health, says the body makes it mainly from another amino acid, glutamine, and that watermelon is the best-known food source. A 2019 review of blood-pressure trials adds that citrulline was first isolated from watermelon, in the 1930s.
More about L-citrulline
The US Office of Dietary Supplements (ODS), part of the National Institutes of Health, says the body makes it mainly from another amino acid, glutamine, and that watermelon is the best-known food source. A 2019 review of blood-pressure trials adds that citrulline was first isolated from watermelon, in the 1930s.
ODS says most of the body's citrulline is turned into arginine, another amino acid, in the kidneys. It states that “the subsequent conversion of arginine to nitric oxide, a potent dilator of blood vessels, might be the mechanism by which citrulline could serve as an ergogenic aid”, meaning an aid to exercise performance. A 2026 review of exercise trials describes citrulline malate as a supplement marketed as that kind of aid.
Supplements come in two forms, ODS says: citrulline on its own, and citrulline malate, which combines citrulline with malic acid, a compound found in many fruits. It reports that most studies of citrulline for exercise have used citrulline malate.
Also known as: citrulline, citrulline malate
At a glance
Safety: known risks and 1 group who should avoid it or take extra care. See Safety ↓Claims made about L-citrulline, and how strong the evidence is for each:
- Improves exercise performanceEvidence rating: Limited
- Reduces muscle soreness after exerciseEvidence rating: Limited
- Lowers blood pressureEvidence rating: Limited
- Improves erectile functionEvidence rating: Insufficient
Each rating follows our published rules and the sources cited for it. We don’t add our own medical judgment. How we rate
Safety
Read this before the ratings below.
Risks
- The US Office of Dietary Supplements states: “Studies have not adequately assessed the safety of citrulline, particularly when users take it in supplemental form for months at a time.” Its summary table reports few safety concerns at the amounts it lists, for use lasting a single day or up to 16 days, and lists gastrointestinal discomfort as the reported adverse effect. Its safety section adds that other short-term studies, which gave citrulline to people who were not athletes for four weeks and for six weeks, found no adverse effects at the amounts those studies used.
- In one trial of 41 weightlifters, 6 reported stomach discomfort after taking citrulline malate. The Office of Dietary Supplements and two of the cited reviews describe this trial.
- Several of the cited reviews note incomplete reporting of adverse events. A 2020 review found that 8 of its 13 trials reported whether side effects occurred, a 2021 review names missing adverse-event reporting as a shortcoming of its trials, and a 2026 review calls for standardized adverse-event reporting in future trials.
- A 2026 review of 12 trials in postmenopausal women, each lasting four to eight weeks, found that none reported adverse effects. Its authors state that “routine clinical use is not yet supported”, citing gaps in long-term safety data among their reasons.
Who should avoid it or take extra care
- Anyone who takes medicines regularly: the Office of Dietary Supplements advises: “Individuals taking dietary supplements and medications on a regular basis should discuss the use of these products with their health care providers.” None of the cited sources describes a specific interaction between citrulline and a medicine.
Safety sources: Source [1]Source [2]Source [3]Source [4]Source [5]
What the evidence says
Each claim is rated on its own evidence. Ratings follow the scale on our methodology page.
Improves exercise performance Evidence rating: Limited
People take it before exercise hoping to push harder, do more repetitions or last longer.
A 2026 review of 30 trials of citrulline malate found a small improvement, rated low certainty; endurance reviews found no significant benefit, and a US health agency says support is not strong.
The reviews report small effects or none; they differ in the form of citrulline and the type of exercise they studied. A 2026 meta-analysis pooled 30 randomized trials of citrulline malate, with 644 participants. It found a small improvement in exercise performance overall, and rated how sure it could be of that (certainty) as low. It describes its evidence base as “dominated by small acute studies in young men”. A single dose before exercise showed a small benefit (low certainty). Taking it over several days showed no significant effect (very low certainty), and perceived exertion did not change significantly (low certainty).
The review adds that apparent benefits for endurance and for short anaerobic efforts were no longer significant once outlying results were removed. Strength and power showed no significant effect, and the reviewers found signs of small-study effects. They conclude that citrulline malate supplementation “may be associated with small, context-dependent improvements in exercise performance, but current evidence remains limited and uncertain.”
A 2021 meta-analysis of eight citrulline malate trials found a small increase in the number of repetitions performed during strength training. After its authors adjusted for possible publication bias, the effect was no longer significant. One of its three authors discloses that he serves as scientific advisor to a manufacturer of sports supplements, a role he began after the manuscript was prepared.
Endurance reviews found no significant benefit. A 2023 meta-analysis of nine trials, most of them using L-citrulline on its own, found none, and notes that the evidence base is small. A 2022 meta-analysis of ten trials found no significant effect on aerobic performance, though its authors describe a positive tendency in longer-term protocols. A 2021 meta-analysis found no effect on endurance in four trials of watermelon juice. Five of its six authors disclose that they were running a separate trial funded by a grant from the International Nut and Dried Fruit Council Foundation; they state that the council did not support the review.
The US Office of Dietary Supplements describes the research on citrulline as an exercise aid as “limited and conflicting at best”. It states: “The research to date does not provide strong support for taking citrulline or citrulline malate to enhance exercise or athletic performance.” This page rates the claim on the lowest certainty the 2026 review gives, very low.
Sources: Source [1]Source [2]Source [3]Source [4]Source [5]Source [6]
Reduces muscle soreness after exercise Evidence rating: Limited
People take it hoping to feel less sore in the days after a hard workout.
A 2020 review of 13 small trials found less soreness 24 hours after exercise; at 48 and 72 hours the difference was not significant, and the review did not grade its certainty.
The evidence is one meta-analysis of small trials. The 2020 review pooled 13 randomized trials in 206 young, healthy, active adults who took citrulline within two hours before exercise. Ten trials used citrulline malate and three used watermelon juice containing citrulline. Most of the trials used resistance or other anaerobic exercise, and the authors caution against applying the results to aerobic exercise.
Muscle soreness was significantly lower 24 hours after exercise, across seven trials. At 48 hours, across six trials, the difference was not significant; it became significant only after the authors excluded one highly influential study. At 72 hours, across four trials, there was no significant difference. The trials differed substantially from one another. The clearest effect the review found was 24 hours after exercise.
The authors conclude: “Citrulline supplements significantly reduced post-exercise RPE and muscle soreness without affecting blood lactate levels.” (RPE is a rating of perceived exertion.) They call for research on longer-term supplementation. The review does not grade its certainty.
The US Office of Dietary Supplements describes one trial in 41 weightlifters taking citrulline malate, in which participants reported significantly less muscle soreness one and two days after exercise. It describes the research on citrulline for exercise overall as “limited and conflicting at best”.
Sources: Source [1]Source [2]
Lowers blood pressure Evidence rating: Limited
People take it hoping it will bring their blood pressure down.
A 2019 review of eight small trials found a modest systolic fall, with no significant overall change in diastolic; a 2026 review in postmenopausal women says “no definitive conclusions can be drawn”.
The two reviews cited here measured blood pressure, not heart attacks or strokes: neither has cardiovascular events as an outcome. A 2019 meta-analysis of eight small trials of L-citrulline supplements, in mostly healthy people, found “a modest but significant” fall in systolic blood pressure. The fall in diastolic pressure was not significant overall. Its authors note that most trials lasted four weeks or less and none had more than 34 participants. They state that “it is still premature to recommend L-citrulline supplementation”.
A 2026 systematic review of 12 small trials in postmenopausal women found reductions in systolic blood pressure in most of the seven that measured it, but did not pool them. Several of the reductions it describes were in pressure measured at the aorta or during exercise. Its results section states: “Overall, citrulline modestly reduced systolic-related BP indices, but effects on resting BP and exercise responses were inconsistent.” Its authors conclude that citrulline may offer benefits for blood pressure in postmenopausal women with high blood pressure, and that “no definitive conclusions can be drawn”.
Neither review grades its certainty. This page’s rating reflects the small number of small, short trials and the reviews’ own cautious conclusions.
Sources: Source [1]Source [2]
Improves erectile function Evidence rating: Insufficient
Men take it hoping it will help with erection problems.
One small pilot trial of citrulline plus transresveratrol, in men on erectile dysfunction medicines, found one questionnaire score higher but not erection hardness; it did not test citrulline alone.
None of the reviews cited on this page addresses erectile function. The cited human evidence is one small pilot trial, and it did not test citrulline on its own. In this 2018 randomized, double-blind, placebo-controlled crossover trial, men took a capsule combining L-citrulline with transresveratrol, or a placebo, for one month each. Their erectile dysfunction had persisted despite PDE5 inhibitor medicines (tadalafil, sildenafil or vardenafil), and they kept taking their medicine. There was no washout period between the two months.
Of 20 men enrolled, 13 completed the study without adverse events; six withdrew, and one could not complete the questionnaire. Scores on one erectile function questionnaire were significantly higher with the combination than with placebo; erection hardness scores did not improve significantly. The authors state that the study did not include citrulline on its own.
Under this site’s rules, an insufficient rating means the cited evidence is too limited to show whether there is an effect; it does not mean the sources found no effect.
Sources: Source [1]
Which form the evidence used
Supplements are sold in several forms. This is what the sources on this page say about them — which form the research used, and any comparison those sources themselves made. Where they made none, this page does not rank the forms.
Citrulline malate (citrulline combined with malic acid), What the sources supportDetails
The US Office of Dietary Supplements (ODS) reports that most studies of citrulline for exercise have used citrulline malate. The 2026 and 2021 citrulline malate reviews cited under exercise performance studied this form only. Of products labeled with a higher share of citrulline, such as citrulline malate 2:1, ODS states that “studies have not determined whether these supplements are superior to standard citrulline or citrulline malate supplements.” The 2026 review cites independent assessments finding that products labeled 2:1 often contain a lower ratio of citrulline to malate than the label states, and the 2021 review reports that two of its trials found less than the labeled content in the product they tested. Source [1]Source [2]Source [3]
L-citrulline on its own, What the sources supportDetails
Most trials in the cited 2023 endurance review used L-citrulline on its own, and the 2019 blood-pressure review studied L-citrulline supplements, excluding watermelon and other citrulline-rich foods. The cited reviews that included both L-citrulline and citrulline malate did not report pooled results separately for each form. The 2026 citrulline malate review describes one crossover trial that compared the two directly and found that neither improved performance in resistance training, and calls for more head-to-head comparisons. Source [1]Source [2]Source [3]
Watermelon juice and other watermelon products, What the sources supportDetails
The cited 2021 endurance review found no effect on endurance performance in four trials of watermelon juice, and reports that the citrulline content of the juice differed considerably between them. The 2020 muscle soreness review included three trials of watermelon juice containing citrulline, one of them also containing compounds from pomegranate, alongside ten of citrulline malate, and did not report results separately by form. The 2026 review in postmenopausal women reports that watermelon products provided less citrulline than pure L-citrulline supplements and gave mixed results, and notes that watermelon contains other compounds that may have effects of their own. Source [1]Source [2]Source [3]
Sources
- Effects of Citrulline Malate Supplementation on Exercise Performance: A Systematic Review and Three-Level Meta-AnalysisNutrients, 2026 · Meta-analysis · Primary source · Certainty: very low
- Acute Effect of Citrulline Malate on Repetition Performance During Strength Training: A Systematic Review and Meta-AnalysisInternational Journal of Sport Nutrition and Exercise Metabolism, 2021 · Meta-analysis · Primary source
- Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysisJournal of the International Society of Sports Nutrition, 2023 · Meta-analysis · Primary source
- Effects of Citrulline Supplementation on Different Aerobic Exercise Performance Outcomes: A Systematic Review and Meta-AnalysisNutrients, 2022 · Meta-analysis · Primary source
- Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trialsJournal of the International Society of Sports Nutrition, 2021 · Meta-analysis · Primary source
- Dietary Supplements for Exercise and Athletic Performance: Fact Sheet for Health ProfessionalsNIH Office of Dietary Supplements, 2024 · Health authority summary · Primary source
- Effect of citrulline on post-exercise rating of perceived exertion, muscle soreness, and blood lactate levels: A systematic review and meta-analysisJournal of Sport and Health Science, 2020 · Meta-analysis · Primary source
- Effects of L-citrulline supplementation on blood pressure: A systematic review and meta-analysisAvicenna Journal of Phytomedicine, 2019 · Meta-analysis · Primary source
- Citrulline supplementation in postmenopausal women: a systematic review of vascular, muscular, and metabolic effectsBMC Women's Health, 2026 · Systematic review · Primary source
- Oral L-citrulline and Transresveratrol Supplementation Improves Erectile Function in Men With Phosphodiesterase 5 Inhibitors: A Randomized, Double-Blind, Placebo-Controlled Crossover Pilot StudySexual Medicine, 2018 · Randomized controlled trial · Supporting source
Page history
Show all 6 changes to this page
- — Rewritten to the content style guideline; ratings and sources unchanged.
- — Revised in the source audit, which applied the rule that a source is cited only once its full text has been read. Two blood-pressure meta-analyses read only from their abstracts, from 2018 and 2025, could still not be read in full and were removed. The blood-pressure summary now reports the two remaining reviews, both read in full, and no longer describes the reviews as disagreeing. The L-citrulline and watermelon form notes no longer cite the removed reviews. No rating changed.
- — Published. All four claims, the safety section and every source passed the site's source and wording reviews. Two blood-pressure reviews read from their abstracts, and four uncited studies, stay logged in docs/08-open-decisions.md.
- — Revised after wording review. The page summary no longer says what citrulline is sold for, and now includes the reviews that found no significant effect. The exercise summary no longer implies that the effect depends on the form of citrulline. The safety section restores that the authority’s statements apply to the amounts studied. Phrases taken from the sources are now marked as quotations. The description of nitric oxide is now attributed to the Office of Dietary Supplements, and a second-hand mention of an excluded erectile-function study was cut. The watermelon form note now notes that one of the soreness review’s three juice trials also contained compounds from pomegranate. No rating changed.
- — Revised after source review. The safety section now separates the durations in the authority’s summary table from its safety section, which also describes studies of four and six weeks. The muscle soreness summary now names the forms the trials used (citrulline malate and watermelon juice) and the number of trials at each time point. The blood-pressure summary no longer describes the full content of the two reviews read from abstracts only, and notes that one abstract does not show whether its overall estimate excludes citrulline-plus-arginine arms. One 2018 blood-pressure review’s disclosures were found and recorded. The erectile-function trial’s participant count now adds up. No rating changed.
- — First drafted. Exercise performance rated limited on GRADE (very low certainty, from the 2026 citrulline malate review); muscle soreness and blood pressure rated limited on review evidence; erectile function rated insufficient, on one small trial of a combination product. No cited source documents a drug interaction.