Tryptophan is an amino acid (protein building block) that the body converts in two chemical steps to serotonin. Serotonin is a neurotransmitter that is frequently unbalanced in depressive individuals. Conventional antidepressants work to increase neurotransmitter levels by blocking their breakdown.
To me, it makes more sense to give the body more building blocks to make more of the serotonin. Tryptophan used to be available at the health food store but a contaminated batch a few years back caused the FDA to pull it off of the market and subsequently make it available by prescription only. I wonder if the drug companies had anything to do with that?
Tryptophan works with accessory nutrients like folic acid. I generally recommend 3 mg of folic acid three times a day. Pyridoxal 5 phosphate (phosphorylated B6) 100-150 mg twice a day is also helpful. The tryptophan dose is about 1500 mg, but can go to 3000 mg usually taken at night. It works really well for insomnia. I have also noticed that many thin individuals or vegetarians are protein deficient and when they start to eat more protein they get more of the essential amino acids and their depression improves without the supplements.