Oral supplementation with a combination of L-citrulline and L-arginine rapidly increases plasma L-arginine concentration and enhances NO bioavailability.

Taking L-citrulline by mouth increases blood levels of L-arginine more than taking the same amount of L-arginine directly.

In rats and rabbits, giving half the usual amount of both L-citrulline and L-arginine together increases plasma nitric oxide metabolites and cyclic GMP more than giving the full amount of either one alone.

When rats and rabbits are given L-citrulline and L-arginine by mouth, their blood levels of L-arginine rise quickly, and giving both amino acids together raises blood L-arginine more than giving either one by itself.

Oral intake of equal halves of L-citrulline and L-arginine increases plasma L-arginine levels and raises nitric oxide metabolites and cyclic GMP in rats and rabbits within hours.

When rats and rabbits are given a combination of L-citrulline and L-arginine at reduced doses by mouth, blood flow in the central ear artery increases compared to when they are not given these substances.

Taking L-citrulline and L-arginine supplements briefly increases nitric oxide-related processes in the body, but this does not lead to measurable improvements in heart health or overall cardiovascular outcomes in people.