Citrulline
Citrulline is an amino acid found in watermelon. The body makes it and converts it into arginine, but does not use it to build proteins.
Also listed as L-Citrulline, Stimol (Brand Name), citrulline malate, Citrulline Malate 2:1
What it is studied for
The strongest rated effects first. Bars show the size of the effect, the letter grades the evidence, and each rating lists the studies behind it.
Why is citrulline linked to blood flow?
The body makes citrulline and converts it to arginine, which can supply nitric oxide. Nitric oxide helps blood vessels widen. This pathway explains the interest in exercise and circulation, but does not by itself prove a supplement benefit. 1
Why people take it
SuppCo community snapshot, 2026-09-28. Reasons for use are not evidence that it works.
Questions people ask
Does better blood flow automatically mean better workouts?
No. The physiological rationale is plausible, while performance reviews find small or inconsistent benefits depending on the outcome and setting. 1 2 3
Is citrulline a proven libido supplement?
The small trial cited here measured erection hardness in men with mild erectile dysfunction. It did not establish increased sexual desire. 4
Is the research dose the same for every form?
No. Citrulline malate includes malic acid, and protocols studying it cannot simply be read as doses of pure L-citrulline. 1 5
Does a study with no side effects prove long-term safety?
No. NIH notes that supplementation over several months has not been adequately studied. 1
Related nutrients
Arginine
L-CarnitineSources
- Dietary Supplements for Exercise and Athletic Performance NIH Office of Dietary Supplements
- Effects of citrulline on endurance performance in young healthy adults: a systematic review and meta-analysis Journal of the International Society of Sports Nutrition, 2023
- 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