The amino acid L-tryptophan is the metabolic precursor of serotonin, a neurotransmitter that carries information from one part of the nervous system to another. It also has a sedative effect. L-tryptophan supplements were once popular as sleep aids, but in 1989 the FDA banned their sale in the United States after a contaminated batch from a Japanese manufacturer was linked to five deaths from eosinophilic myalgia syndrome, a rare and painful disease. To date, the FDA has not lifted its ban.
Taking a veterinary L-tryptophan supplement should be safe, but I think there are better remedies for insomnia, premenstrual syndrome, and jet lag, the problems for which it was recommended. I don't advise taking any sleeping aids, natural or not, on a regular basis - if that's why you want to take L-tryptophan, I suggest that you go another route. Much insomnia results from stress, anxiety, depression and the use of stimulant drugs, so you would be better off addressing those issues.
You can improve your sleep, combat stress, depression and even PMS with regular aerobic exercise, breathing exercises and practicing relaxation techniques.
Instead of L-tryptophan, try taking Valerian (Valeriana officinalis) as a temporary sleep aid. For PMS, avoid caffeine, take up to 700 mg of calcium and 350 mg of magnesium for painful menstrual cramps, along with 500mg of black currant oil or evening primrose oil twice a day and two capsules of dong quai or chaste tree twice a day.
For jet lag, I take 2.5 mg to 3.0 mg of melatonin sublingually (under-the-tongue) at bedtime for one or two nights after arrival.
Andrew Weil, M.D.