5-Hydroxytryptophan is the intermediate between tryptophan and serotonin. Supplements bypass tryptophan hydroxylase, the rate-limiting enzyme.
Mechanism — Crosses the blood-brain barrier and is decarboxylated to serotonin. Raises CNS serotonin acutely. Useful for sleep onset, mood support, and some appetite-suppression effects.
Use case — Sleep onset (100-200 mg 30 min before bed) or mood (50-100 mg morning). Don't combine with SSRIs or other serotonergic drugs.
Caveats — Serotonin syndrome risk with stacking. Long-term high-dose use may deplete dopamine — cycle and consider pairing with EGCG or carbidopa in nutrition-aware contexts. Don't run continuously for months.