L-citrulline is an amino acid found in watermelon. It is also produced within the body. L-citrulline is converted by the body into L-arginine, another amino acid.

The name citrulline comes from Citrullus vulgaris, the Latin term for watermelon. L-citrulline, unlike some amino acids, is not utilised to produce protein, but it may help enhance other chemicals required by the body to make protein. It may also enhance blood flow and lower 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, but there is no good scientific evidence to support most of these uses.