Oral L-citrulline supplementation results in higher plasma L-arginine concentrations compared to equivalent oral doses of L-arginine.

Study: Pharmacokinetic and pharmacodynamic properties of oral L-citrulline and L-arginine: impact on nitric oxide metabolism.

Taking L-citrulline pills raises arginine levels in your blood better than taking arginine pills directly, because your body absorbs and uses citrulline more efficiently.

Study: Effect of oral citrulline supplementation on whole body protein metabolism in adult patients with short bowel syndrome: A pilot, randomized, double-blind, cross-over study.

Taking L-citrulline by mouth turns into more L-arginine in the blood than taking L-arginine directly, because the body processes citrulline more efficiently. This study showed that citrulline made blood arginine levels jump three times higher.

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

Taking L-citrulline turns into more arginine in your body than taking arginine directly, because arginine gets broken down too fast in the gut and liver — but citrulline doesn’t, so it delivers more arginine to your blood.