Outcome
    Moderate Evidence

    Glycine for Melatonin Production

    Glycine 3 g before bed improves sleep onset and quality in RCTs, partly by lowering core temperature — complementing rather than driving melatonin synthesis.

    Overview

    Glycine 3 g before bed improves sleep onset and quality in RCTs, partly by lowering core temperature — complementing rather than driving melatonin synthesis.

    How It Works

    NMDA receptor co-agonist with suprachiasmatic effects; promotes peripheral vasodilation and core temperature drop, the thermal signal that triggers sleep onset.

    Dosing & Protocol

    Typical dose

    Recommended dose
    3 g powder in water, 30–60 min before bed.
    Expected timeframe
    Not established

    Protocol

    form
    Not applicable
    duration
    Not applicable
    co factor
    Evidence is insufficient, and this appears to be a mechanistic mix-up. Glycine does improve sleep onset at 3 g before bed, but the demonstrated mechanism is peripheral vasodilation lowering core body temperature, together with NMDA receptor action in the suprachiasmatic nucleus - not melatonin. No human study has measured melatonin or its metabolite 6-sulphatoxymelatonin after glycine supplementation, and glycine is not a precursor in the melatonin synthesis pathway, which runs from tryptophan through serotonin to melatonin. If raising melatonin is the goal, melatonin itself, tryptophan and evening light restriction are the relevant levers.
    titration
    Not applicable
    starting dose
    Not applicable for this outcome

    Evidence

    What the studies say

    RCTs show 3 g glycine before bed shortened sleep-onset latency, improved sleep quality scores, and reduced next-day fatigue. Mechanism is thermoregulatory/circadian rather than melatonin synthesis per se.

    No studies are yet linked to both Glycine and Melatonin Production.

    Safety

    Caveats

    Very safe; mild GI upset rare. Powder tastes mildly sweet.

    Less likely to help if

    Shift workers with light-driven circadian disruption need light management as the primary fix.

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