Although named and described by gastroenterologists since the late 19th century, it was first isolated from watermelon in 1914 by Japanese researchers Yatarō Koga (古賀彌太郎) and Ryō Ōtake (大嶽了)[3][4] and further codified by Mitsunori Wada of Tokyo Imperial University in 1930.

[9] It is also prevalent in trichohyalin at the inner root sheath and medulla of hair follicles, where it is synthesized from arginine.

In the yeast species Saccharomyces cerevisiae, citrulline is a metabolic intermediate in the latter, cytosolic half of the arginine biosynthesis pathway.

These assertions are based on animal studies, and like most dietary supplement claims have not be endorsed by the Food and Drugs Administration.

[15] L-citrulline is added to certain energy drinks such as Reign and touted for its thermogenic effects.