Administration of 4 grams of L-citrulline from microencapsulated watermelon rind in healthy young adults results in a vascular response that peaks at 60 minutes and returns to baseline by 120 minutes, indicating a transient pharmacological effect rather than a sustained physiological change.

When L-citrulline is swallowed, it enters the bloodstream and is turned into L-arginine in the kidneys. L-arginine then moves to blood vessel walls, where it is used to make nitric oxide. Nitric oxide tells the muscle around the blood vessels to relax, making the vessels wider and increasing blood flow. This effect lasts only as long as L-citrulline and L-arginine stay high in the blood, which is about two hours.