Taking a specific amino acid called L-citrulline twice a day for a week boosts a related chemical in your blood more than taking that chemical directly, which might help your body make more of a molecule that relaxes your blood vessels.

Taking a specific amino acid called L-citrulline twice a day for a week helps raise levels of another amino acid, L-arginine, in the blood more than taking L-arginine directly—this might help your body make more nitric oxide, which is good for blood flow.

Taking a specific supplement called L-citrulline every day for a week, plus a little more before working out, can boost a key chemical in your blood by about three-quarters — and that chemical helps your body make nitric oxide, which is good for blood flow.

Taking a specific amino acid supplement called L-citrulline twice a day for a week helps healthy people with high levels of a certain compound in their blood to produce more of a helpful molecule that improves blood flow.

Taking a specific amino acid supplement called L-citrulline twice a day for a week can help improve a key balance in your blood that lets your body make more nitric oxide — a molecule that helps your blood vessels relax and work better.

Taking L-arginine pills in these amounts doesn’t raise the levels of L-arginine or related molecules in your blood or urine, because your body breaks them down too quickly before they can get into your system.