5-Hydroxy-Tryptophan, or 5-HTP for short, is the precursor to a neurotransmitter called serotonin. Serotonin is responsible in part for regulating mood, appetite, and sleep cycles, and low levels of it are associated with depression, food cravings (especially carbs), and insomnia.

During the luteal phase of one's menstrual cycle - in other words, the week before one has their period, PMS time - serotonin levels drop sharply, leading to crankiness and persistent food cravings. (There're other hormonal factors responsible for PMS as well, but lack of serotonin is chiefly at fault for those "shovel food into your mouth with one hand and give somebody the finger with the other hand" urges.) Again, 5-HTP is the precursor to serotonin, so by supplementing it where your body fails to produce enough, you get less PMS symptoms.

It's not just helpful around that time of the month, though - 5-HTP can be taken at any time for appetite suppression, as a sleep aid, or simply for overall well-being. It's especially helpful on low carb diets, too - carbohydrates are needed to synthesize serotonin, and in the absence of them, the body will inherently be producing less of this important neurotransmitter.

When and how much to take depends on what you're using 5-HTP for. For improved mood and blunted appetite, 50-150 milligrams daily is sufficient, first thing in the morning. To treat insomnia, doses of 150-300 milligrams about an hour before bedtime are generally used. The only trick to maximizing 5-HTP effectiveness is to take it on an empty stomach, as far away as possible from meals containing protein. Tryptophan is an amino acid, and may compete with other aminos in protein for uptake.

On a personal note, this stuff has been a godsend for me. I wouldn't wax ecstatic about it otherwise. I used to be a basket case for almost a good 2 weeks out of the month, and have the worst time with food cravings while cutting irrespective of where I was in my menstrual cycle, but supplementing with 5-HTP has made me do a complete 180. I now have what could remotely be construed as PMS for a day tops every cycle, and I'm a much calmer and smiley-er person. I've also got my (post-menopausal) mother on the 5-HTP train - she takes it for stress management when her job occasionally gets crazy, and has dropped a considerable amount of weight because she's not eating to feed emotions anymore. Besides r-ALA, this is the only OTC supplement I could not live without.