Asymmetric dimethylarginine (ADMA) is a naturally occurring chemical found in blood plasma. It is a metabolic by-product of continual protein modification processes in the cytoplasm of all human cells. It is closely related to L-arginine, a conditionally-essential amino acid. ADMA interferes with L-arginine in the production of nitric oxide, a key chemical involved in normal endothelial function and, by extension, cardiovascular health.

Nitric oxide (NO) is synthesized in endothelial cells by the enzyme endothelial nitric oxide synthase. The production rate of NO is a key factor for endothelial and cardiovascular functions. The substrate of endothelial nitric oxide synthase is Arg, which is converted into the products NO and citrulline. The enzyme is inhibited by the endogenous Arg metabolite asymmetric dimethylarginine (ADMA).