L-5HTP treatment and serum 5-HT level after L-5-HTP loading on depressed patients.

Based on 5-HT hypothesis, L-5-HTP (150 or 300 mg/day) was given orally to 18 depressed patients. The global estimates were 2 very much improved; 8 much improved; 3 minimally improved, and 5 unchanged. The action of L-5-HTP was usually rapid. The elevation of the serum 5-HT level 1 week after L-5-HTP administration was relatively lower in the 5-HTP nonresponder group, compared with the responders. The chronological change of the serum 5-HT level in depressed patients after an oral loading dose of 3 mg/kg of L-5-HTP showed a gradual and slight elevation, compared with manic and normal groups. It seemed that the therapeutic effect of L-5-HTP on responders was related to lower 5-HT level in the brain for their pathogenesis, and that there was a metabolic disturbance of L-5-HTP into 5-HT in some depressed patients.