L-citrulline boosts nitric oxide production in the body. Nitric oxide helps your arteries relax and work better, which improves blood flow throughout your body. This may be helpful for treating or preventing some diseases. There is some evidence to suggest the supplement could possibly help lower blood pressure in people with prehypertension. This is an early warning sign for high blood pressure. It means you have a slightly raised blood pressure reading of 120/80 to 139/89. Prehypertension raises your risk for high blood pressure and heart disease. L-citrulline supplements may ease symptoms of mild-to-moderate erectile dysfunction (ED). Scientists say L-citrulline does not work as well as ED drugs such as Viagra. However, it appears to be a safe option. Animal studies suggest L-citrulline might also help people with blood vessel problems such as slow wound healing due to diabetes. Other animal research says L-citrulline might improve muscle protein levels and prevent malnourishment in the elderly.