Melatonin

Also known as INDOLE, 3-(2-ACETAMIDOETHYL)-5-METHOXY, SEROTONIN, N-ACETYL-O-METHYL, ACETAMIDE, N-[2-(5-METHOXYINDOL-3-YL)ETHYL], N-ACETYL-5-METHOXYTRYPTAMINE, 3-(2-ACETAMIDOETHYL)-5-METHOXYINDOLE

This is the body's own sleep-related pineal hormone, and its active dose is hard to pin down because the endpoint is falling asleep rather than any enhancement of consciousness. One person taking 80 mg drifted quickly into natural, sound sleep and woke with improved mood and performance, while a tiny intravenous dose produced no subjective effect; it is widely marketed for sleep and jet-lag and tied to light exposure, mood, seasonal depression, and sleep-phase timing.