A double-blind, randomized, placebo-controlled cross-over study conducted by researchers at the University Medical Centre Hamburg-Eppendorf, Germany showed oral L-citrulline increased L-arginine blood levels and boosted nitric oxide-dependent signaling and therefore levels of cGMP much more effectively than L-arginine.
Other studies have confirmed that supplementing with L-citrulline can actually reverse blood vessel lining dysfunctions!