A nutritional supplement that is synthesized from adenosine triphosphate (ATP) and the amino acid methionine by the endogenous essential enzyme methionine adenosyltransferase (MAT), with potential antineoplastic activity. Upon administration, S-adenosylmethionine acts as a methyl donor for various transmethylation reactions. In cancer cells, this agent induces the methylation of tumor promoting genes, reverses DNA hypomethylation, and leads to the suppression of oncogene transcription. This induces apoptosis in and inhibits proliferation of susceptible tumor cells.

Physiologic methyl radical donor involved in enzymatic transmethylation reactions and present in all living organisms. It possesses anti-inflammatory activity and has been used in treatment of chronic liver disease. (From Merck, 11th ed)

S-Adenosyl-l-methionine (SAMe) is a derivative of methionine and a cofactor for multiple synthetic pathways, particularly as a methyl group donor. It is produced naturally in the body, mainly by the liver, and is manufactured synthetically in supplement form.