Nitric oxide (NO) mediates vasodilation and blood flow. Complete guide to NO-supporting supplements — L-Arginine vs L-Citrulline, mechanism and clinical evidence.
Nitric oxide (NO) is a vasodilator produced from L-Arginine by nitric oxide synthase (NOS) enzymes. L-Citrulline is more efficiently converted to L-Arginine than oral L-Arginine itself (due to first-pass liver metabolism), making L-Citrulline the superior NO precursor for oral supplementation.
Nitric oxide (NO) is a gaseous signalling molecule produced in vascular endothelium by nitric oxide synthase (NOS) enzymes acting on L-Arginine. NO signals vascular smooth muscle to relax, producing vasodilation — increased blood vessel diameter and improved blood flow. This mechanism underlies many of the benefits associated with L-Arginine supplementation.
Oral L-Arginine is substantially metabolised by the liver before reaching systemic circulation (first-pass effect), limiting its effectiveness as a direct NO precursor. L-Citrulline bypasses liver metabolism and is converted to L-Arginine in the kidneys with higher efficiency. For oral supplementation aimed at NO production, L-Citrulline consistently outperforms L-Arginine in published studies.