Metathione is a brand name for the amino acid glutathion. It is a potent antioxidant and may help prevent or treat the severe weight loss (cachexia) in advanced HIV/AIDS disease. It is considered safe in doses up to 600 mg/day but it is not recommended for pregnant or nursing women. Some people believe it will lighten the skin.

You might mean methionine, another amino acid and antioxidant , usually sold as SAM-e, a sufur based form of this amino acid. Research is still being done, but SAM-e may be useful in treating conditions such as depression and inflammatory diseases like arthritis. It is for sale over the counter and generally considered safe. but may raise the blood levels of certain compounds associated with heart disease risks.

Anyone with health issues should discuss use of these products with a physician and recommended doses should not be exceeded.