Sam-E is s-adenosylmethionine (I think - too lazy to check). Its a substance that is a precursor to Serotonin (and other neurotransmitter) production.
Supposedly our diets are very poor with it, and I read claims that flouride in toothpaste also uses it up. Not sure as to the validity of either statement.
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Btw, Yoga, while it helps a lot with mood, is not a pill .