Citrulline produces several important effects in the body. One major way it works is by increasing vasodilation. Vasodilation refers to the widening of arteries or veins. It’s associated with lower blood pressure and increased blood flow.

After citrulline is consumed, some is converted to another amino acid called arginine. Arginine is converted into a molecule called nitric oxide, which causes vasodilation of blood vessels by relaxing the smooth muscle cells that constrict them. Interestingly, consuming citrulline may increase arginine in the body more than consuming arginine itself. This is because of differences in how the body processes and absorbs arginine and citrulline.

The increase in nitric oxide and blood flow may be one of the processes involved in citrulline’s beneficial effects on exercise performance. Although citrulline isn’t an amino acid used directly to build proteins, it has been shown to increase protein synthesis by stimulating an important signaling pathway involved in muscle building. Citrulline may also reduce the liver’s uptake of certain amino acids and prevent their breakdown. Through these dual effects on protein synthesis and amino acid breakdown, it may contribute to maintaining or increasing muscle mass.