5-hydroxytryptophan (5-HTP) is the natural immediate precursor of serotonin (5-HT). 5-HTP levels determine 5-HT synthesis and 5-HT levels.
EVX-101 contains pure 5-HTP derived from the African plant Griffonia Simplicifolia. Griffonia seeds naturally contain high levels of 5-HTP.
Several pilot studies report that adjunctive treatment with 5-HTP augments antidepressant efficacy. In the above study by Dr. Herman van Praag, 4 times daily 5-HTP/carbidopa augmented the efficacy of clomipramine, an SSRI-like antidepressant (van Praag, Adv Biochem Psychopharm, 1982).
5-HTP has shown therapeutic promise in many illnesses, most notably in depression, but also in obesity, fibromyalgia, and myoclonus, to name a few.
5-HTP appears safe in humans. Serious side effects have not been reported with 5-HTP administration in humans, even at doses many-fold the doses projected for EVX-101.
However, the rapid absorption of 5-HTP is associated with bothersome gastrointestinal side effects, and the short half-life (2h) necessitates multiple daily doses to maintain efficacy, which is impractical during general therapy. See above schematic figure representing 5-HTP plasma levels at 3 daily doses.
5-HTP's poor 'druggability' is probably why no FDA-approved 5-HTP drug has previously been developed.