APA Dictionary of Psychology

n. a nonprotein chemical compound that mediates numerous metabolic reactions, including those involving certain proteins, phospholipids, neurotransmitters, and nucleic acids. It is commonly used as a dietary supplement in the treatment of depression because it may increase levels of serotonin in the brain. It also has been implicated in Alzheimer’s disease: Low S-adenosylmethionine levels often are observed in those with the disease, which may be a sign of altered SAM metabolism.