What it is
Regulatory status: amino acid and dietary supplement ingredient; not an FDA-approved insomnia treatment
Mechanism evidence: human
At a glance
What it is, why people use it, the evidence, and what to know before trying it.
Why people use it
- Subjective sleep quality (satisfaction, “slept well,” sleep efficiency by questionnaire).
- Faster sleep onset / shorter latency to slow-wave sleep (PSG).
- Lower core body temperature at bedtime (sold as the reason it works).
- Less next-morning fatigue / more clear-headedness.
- Less daytime sleepiness after a short or poor night.
- Better next-day vigilance / memory after sleep restriction.
- Better insulin sensitivity / lower post-meal glucose / lower HbA1c.
- Higher glutathione / lower oxidative stress.
- Joint / cartilage / collagen support (often via a collagen scoop counted as “glycine”).
- Metabolic-syndrome improvements (blood pressure, lipids, waist).
Evidence at a glance
**Track A (2–3 g at night for sleep).** Three tiny manufacturer RCTs (analysed **n=19, 11, and 7**) show a consistent *direction*: 3 g ~30–60 min before bed improved some next-morning fatigue / clear-headedness scores and, in one single-blind PSG night, shortened latency to stage 2 and stage 3 without changing architecture. Daytime sleepiness was a trend, not a clear win (Bannai VAS P=0.098; gone by day 3). **2 g has never been tested. Core temperature has never been measured in humans.** Confidence: **weak**. What would change this: one adequately powered, independently funded, double-blind PSG+CBT trial in people with insomnia (not company staff), 3 g vs 2 g vs placebo, with numeric SOL in minutes and a pre-registered primary endpoint.