"Many ecstasy users claim that the amino-acid supplement, 5-Hydroxy-Tryptophan (5-htp), helps lessen post-E depression. 5-htp is the direct precursor to serotonin in your body. Your body produces it on its own in the process of creating serotonin. It is not a drug, but an amino-acid, and is currently sold in most health food stores as an herbal supplement (extracted from Griffonia seeds). Clinical studies of 5-htp have demonstrated that it does relieve symptoms of depression in many people. It does this by increasing the amount of 5-htp in the brain, thus making it easier for the brain to make serotonin. Supplementing with 5-htp may, therefore, lessen post-E depression by helping your body restore its serotonin levels more quickly."

personal experience

i've taken this resently to offset the depression that is associated with MDMA use (usually about 24-48 hours after comedown), and found it to work really well. also noticed what seemed to be deeper and more refreshing sleep. combined with exercise, i'd say this could possibly be a general, cheap, and effective anti-depressant.

note: i am not a chemist.