L-citrulline is an amino acid found in watermelon. It is also made in the body. The body changes L-citrulline into another amino acid called L-arginine.

The name citrulline comes from Citrullus vulgaris, the Latin term for watermelon. Unlike some amino acids, L-citrulline isn't used to make protein, but it might help increase other chemicals the body needs to make protein. It might also help improve blood flow and reduce blood pressure.

People use L-citrulline for athletic performance, sickle cell disease, erectile dysfunction (ED), high blood pressure in the lungs, heart disease, and many other conditions.