S-Adenosylmethionine (SAMe) is a naturally occurring compound that is found in almost every tissue and fluid in the body. SAMe is involved in many essential processes. SAMe plays a role in maintaining the cell membranes, the immune system, and helps produce and break down brain chemicals, such as serotonin, melatonin, and dopamine. SAMe works with vitamin B12 and folate (vitamin B9). Being deficient in either vitamin B12 or folate may reduce SAMe levels in your body.