S-Adenosyl-L-methionine- 13 C is the 13 C labeled S-Adenosyl-L-methionine. S-Adenosyl-L-methionine (S-Adenosyl methionine) is produced endogenously from methionine and ATP by action of the enzyme methionine adenosyltransferase and is an important orally active methyl group donor. S-Adenosyl-L-methionine is a dietary supplement with potent antidepressant effects, and has the potential for liver disease and osteoarthritis research.