Glycine

What does glycine do?

Glycine is the smallest amino acid the body uses, and it serves multiple roles. It's a building block of collagen (which is why bone broth and connective tissue are rich sources). It's a co-agonist at NMDA receptors. And critically for sleep, it acts as an inhibitory neurotransmitter at glycine receptors, particularly in the brainstem.

The most likely mechanism behind glycine's sleep effects is its action on core body temperature. Falling asleep requires a drop in core body temperature; this is part of why a warm bath an hour before bed can help. Glycine appears to facilitate this drop by promoting vasodilation in the extremities, allowing the body to shed heat. Polysomnographic studies show that glycine before bed reduces sleep onset latency and increases the time spent in slow-wave sleep, suggesting an effect on actual sleep architecture rather than just subjective perception.

What the research shows

Three controlled trials anchor the evidence base:

Inagawa et al. (2006, Journal of Clinical Sleep Medicine) found that 3 grams of glycine before bed in adults with mild sleep complaints significantly reduced sleep onset latency and improved subjective sleep satisfaction.

Yamadera et al. (2007, Sleep and Biological Rhythms) used polysomnography to confirm that 3 g of glycine before bed reduced sleep onset latency and improved subjective sleep quality, with the polysomnographic data showing measurable changes in sleep architecture.

Bannai et al. (2012, Journal of Pharmacological Sciences) extended these findings, showing that 3 g of glycine before bed improved sleep efficiency, increased REM sleep, and reduced sleep latency.

A follow-up study examined daytime performance after partial sleep restriction. Subjects given 3 g of glycine before sleep showed reduced fatigue and improved psychomotor vigilance test performance compared to placebo, suggesting the benefits extend beyond just feeling more rested.

The effect size is modest in absolute terms — these aren't dramatic sedative effects — but the consistency across studies and the combination of subjective and objective improvements is unusual for a natural sleep aid.

Considerations and unknowns

The 3-gram dose used in research is significantly larger than what you'd get from food (a typical serving of bone broth provides only a few hundred milligrams) but still well within safety limits. A 9-gram safety study found no serious adverse events at three times the standard dose.

Glycine has a faintly sweet taste, which makes the powder form palatable in water. Capsules require taking 4-6 large capsules to reach 3 grams, which some people find inconvenient.

Existing supplement overlap: magnesium glycinate (a chelated form of magnesium bound to glycine) already contains some glycine, though typical sleep doses of magnesium glycinate provide far less than 3 grams of glycine.

Most studies have run for short durations (a few nights to a few weeks). Long-term daily use of supraphysiological glycine doses has not been extensively studied, though no safety signals have emerged.

People taking clozapine (an antipsychotic) should avoid supplemental glycine, as it can interfere with the medication's effectiveness. Otherwise, glycine has very few known drug interactions.

Studies have generally been small (10-20 subjects) and conducted on populations with mild sleep complaints rather than diagnosed insomnia. Effects in severe insomnia or chronic sleep disorders are less well established.

How to evaluate quality

Glycine is one of the simpler supplements to evaluate. It's a single amino acid produced by reliable industrial fermentation processes and verified easily by standard lab tests.

Look for products that:

• Are third-party tested (USP, NSF, or ConsumerLab certifications)
• List “glycine” or “L-glycine” as the only active ingredient (avoid proprietary blends if you want to dose precisely)
• Are produced in cGMP-certified facilities
• Have minimal additives — pure glycine powder is essentially flavorless to faintly sweet, no need for fillers or flavorings

Pharmaceutical-grade glycine is widely available at low cost; you don't need to pay a premium for this one.

Where to Buy

Glycine is widely available as both bulk powder and capsules. Powder is more economical and easier to dose at the 3-gram research-supported level.

FAQ