L-citrulline is an amino acid the body makes and gets from food such as watermelon; the kidneys turn most of it into arginine, which the body uses to make nitric oxide, a blood-vessel dilator. As a supplement, often as citrulline malate, it is used to try to improve exercise performance.
Also known as: L-citrulline, citrulline malate.
Citrulline has no intake value or upper limit. ODS describes a trial that used 8 g of citrulline malate 1 hour before exercise, and short studies in non-athletes of up to 6 g a day for 4 weeks. Citrulline malate is 56.64% citrulline by weight, so 1 g of citrulline malate provides 566 mg of citrulline. These are study protocols, not a recommendation.
It is sold in the US as a dietary supplement. Under the 1994 dietary supplement law (DSHEA), FDA does not approve dietary supplements before they are marketed, and the maker, not FDA, is responsible for safety and labeling. There is no FDA-approved citrulline drug.
The NIH Office of Dietary Supplements (ODS) calls the research on citrulline for exercise limited and conflicting: in one trial of 41 weightlifters, 8 g of citrulline malate allowed more bench-press repetitions and less soreness, while in another study citrulline without malate led to worse treadmill performance than placebo. ODS concludes the research does not strongly support it for exercise or athletic performance. Studies have not shown that "2:1" or tri-citrulline malate products work better than standard ones.
ODS says safety has not been adequately studied for use over months; in the weightlifter study 6 of 41 people had stomach discomfort, and short studies at up to 6 g a day for 4 weeks found no adverse effects. In a pharmacokinetic study of 8 healthy men (Moinard 2008), single doses of 2 to 15 g caused no side effects and raised blood arginine, though at the highest doses arginine rose less than expected.
In 8 healthy men given 2 to 15 g (Moinard 2008), blood arginine peaked about 1.2 to 2.3 hours after the dose, depending on the amount, and less than 5% of the citrulline was lost in urine. The abstract does not give a half-life or time to peak for citrulline itself, so we do not list one.
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