The body converts L-citrulline to L-arginine, another type of amino acid. L-arginine improves blood flow. It does so by creating nitric oxide (NO), a gas that helps dilate blood vessels. L-arginine has been shown to help people with heart disease or clogged arteries because of its vessel-widening abilities.
The same effect on blood vessels helps improve symptoms of erectile dysfunction (ED). The L-citrulline to NO path increases blood flow to a man’s genitals. In one study, this increase in blood flow appeared to decrease symptoms of mild ED and improve the ability to maintain an erection. There haven’t been any studies on the use of L-citrulline in moderate to severe cases of ED.