S-Adenosylmethionine (often referred to as SAMe) is a methyl donor and a cofactor for enzyme-catalyzed methylations, including catechol O-methyltransferase (COMT) and DNA methyltransferases (DNMT). Although present in all cells, it is concentrated in liver where 85% of all methylation reactions occur. SAM is anti-apoptotic in normal hepatocytes and normal colon epithelial cells but pro-apoptotic in liver human hepatocellular carcinoma (HCC), HepG2 cells and colon cancer cells. Because of structural instability, stable salt forms of SAM are required for its use as an oral drug. The commonly used salts: tosylate, butanedisulfonate, disulfate tosylate, disulfate ditosylate, and disulfate monotosylate. SAMe has been marketed in some European countries since the mid-1980s for the treatment of depression and for other medical conditions such as osteoarthritis (joint disease that causes joint pain and stiffness), fibromyalgia (widespread pain and stiffness). In addition, it is used to treat liver disease and migraine headaches. However, it is not formally approved in the UK for the treatment of depression, and in the USA, it is classified only as a dietary supplement. Some research suggests that it is more effective than placebo in treating mild-to-moderate depression and is just as effective as antidepressant medications without the side effects (headaches, sleeplessness, and sexual dysfunction). In addition, antidepressants tend to take 6 to 8 weeks to begin working, while It seems to begin more quickly. Researchers are not sure how SAMe works to relieve depression. But they speculate it might increase the amount of serotonin in the brain just as some antidepressants do. Many studies have examined injectable forms of SAMe, not oral supplements.