I got this from WebMD.com, it explains it better than I can.
SAM-e is short for S-adenosylmethionine, a substance naturally occurring in the cells of plants and animals. SAM-e is not an herb. Because the body produces less SAM-e with age, some people think that SAM-e may be a helpful supplement for certain diseases. In the United States, it is sold as a dietary supplement.
All that is in it is S-adenosylmethionine, nothing else. Some people also believe that it promotes healthy liver function and helps with joint pain. All I know is that as far as my depression, it changed my life.
I also gave it to my son, who has been diagnosed as ADHD, and it made all the difference for him. He is able to focus, he is calm without the "mushroom effect" and he isn't having the bad side effects like loss of appetite, aggression and depression, that the scripts cause.