5-hydroxy-L-tryptophan (5-HTP), a byproduct of L-tryptophan, is used to produce serotonin. Serotonin is a neurotransmitter (a natural chemical in the brain) that is important for sleep, positive moods, and for a number of other conditions essential for well-being.
There have been many claims and some studies reporting benefits of L-tryptophan and 5-HTP for insomnia, headache, and depression, although the evidence supporting these benefits is still weak.
It should be strongly noted that products containing both of these substances are not regulated and have been associated with impurities that cause a serious and in some cases fatal blood disease called eosinophilia-myalgia syndrome (EMS).
L-tryptophan products are no longer available in the U.S. 5-HTP, however, is available in supplements and is also found in the herb Griffonia. 5-HTP should not be taken in high doses.