Glycine

amino acid

Best in the morningTake with food

What is it

Glycine is the smallest amino acid, classified as conditionally essential because the body can synthesize it from serine and other precursors but at rates that may not meet demand in adults. It is a major structural component of collagen and also functions as an inhibitory neurotransmitter in the brain and spinal cord.

How it works

Glycine wears several hats. About one-third of all amino acids in collagen are glycine, which is why it is critical for skin, joints, tendons, and bones. It is a precursor to glutathione (the body's primary antioxidant), creatine, heme (the iron-carrying group in hemoglobin), and bile acids. In the central nervous system, glycine acts as an inhibitory neurotransmitter at glycine receptors in the spinal cord and brainstem, helping to dampen motor and sensory excitability. In the brain itself, glycine paradoxically acts as a co-agonist at NMDA glutamate receptors, where it helps modulate excitatory signaling. Oral glycine at gram-level doses appears to influence sleep onset and quality, possibly by mildly lowering core body temperature and through serotonergic and NMDA-receptor mechanisms. The body's daily endogenous synthesis of glycine has been estimated at roughly 2 to 3 grams, which is well below total daily needs for protein turnover, collagen renewal, and metabolic functions. Researchers have argued that glycine intake from a typical Western diet may be insufficient relative to ideal turnover, which is one reason interest in glycine supplementation has grown.

Evidence for 5 uses

AI-assisted evidence assessment — talk to your doctor before relying on any single supplement.

Sleep quality and subjective sleep satisfaction

Grade B

Good evidence

Multiple randomized trials by Japanese researchers found 3 grams glycine before bed improved subjective sleep quality, reduced sleep onset latency, and reduced next-day fatigue and sleepiness in adults with mild sleep complaints. Polysomnography showed faster entry into deep sleep. Evidence base is reasonably strong for this specific use.

Collagen synthesis and joint support

Grade C

Moderate evidence

Glycine is the most abundant amino acid in collagen, and supplementation may support collagen turnover in skin, tendons, and joints. Direct trials of glycine alone for joint outcomes are limited; the strongest evidence supports glycine as part of collagen peptide formulations.

Metabolic syndrome and glycemic control

Grade C

Moderate evidence

Small trials suggest glycine supplementation (5 to 15 g/day) may modestly improve insulin sensitivity and reduce inflammatory markers in adults with metabolic syndrome or type 2 diabetes. Larger trials are needed to confirm and quantify effects.

Schizophrenia (negative symptoms, adjunctive)

Grade C

Moderate evidence

High-dose glycine (up to 60 g/day) as add-on to non-clozapine antipsychotics has shown reductions in negative symptoms (apathy, social withdrawal) in some trials but not others. Must be done under psychiatric supervision and avoided with clozapine.

Glutathione production and antioxidant capacity

Grade C

Moderate evidence

Glycine is one of three amino acids needed to make glutathione, the body's main intracellular antioxidant. Studies combining glycine with N-acetylcysteine (GlyNAC) have shown improvements in glutathione levels, oxidative stress markers, and mitochondrial function in older adults.

3 commercial forms

Glycine powder

Rapidly absorbed; well tolerated even at gram-level doses.

The most common form. Naturally sweet taste makes it easy to mix in water or tea. Cost-effective for higher daily totals.

Glycine capsules

Same bioavailability as powder; convenient but limited per-dose amount.

Typically 500 to 1,000 mg per capsule. For 3 to 5 gram bedtime doses, powder is more practical.

GlyNAC (glycine + N-acetylcysteine)

Combination targets glutathione synthesis; both amino acid building blocks delivered together.

Emerging research-driven combination for mitochondrial health and oxidative stress in older adults. Often dosed at 100 mg/kg each.

Dosage

There is no RDA. Typical supplement doses are 3 to 5 grams before bed for sleep, 5 to 15 grams divided across the day for collagen and metabolic support, and up to 0.8 grams per kilogram body weight in high-dose research protocols. Schizophrenia trials have used up to 60 grams per day under clinical supervision. Most consumer products provide 1 to 3 grams per scoop.

When and how to take it

For sleep, take 3 grams of glycine in water 30 to 60 minutes before bed. The flavor is naturally sweet, so most people take it straight or in tea. For collagen, joint, and metabolic support, split larger daily totals (5 to 15 grams) across the day with meals to maintain steady availability for collagen synthesis. Glycine pairs well with collagen peptides because the peptides themselves contain about 22 percent glycine. Morning doses are fine; despite the bedtime evidence, glycine does not cause significant daytime drowsiness for most users.

Food sources

Food	Amount	%DV
Pork rinds (1 oz)	~3 g	—
Bone broth (1 cup)	~2 to 4 g	—
Chicken skin (1 oz)	~0.8 g	—
Beef (3 oz)	~1.3 g	—
Salmon (3 oz)	~1 g	—
Gelatin (1 tbsp)	~1.6 g	—
Eggs (1 large)	~0.25 g	—

Safety

Glycine is very well tolerated. The most common side effect is mild gastrointestinal upset (loose stools, nausea) at doses above 5 grams, often resolved by splitting the dose. No Tolerable Upper Intake Level has been formally set. Single doses up to 9 grams and chronic daily intakes of 31 grams have been used safely in research. Sweet taste makes it easy to take in water. People taking clozapine should avoid high-dose glycine because the combination has reduced clozapine's antipsychotic efficacy in some patients. Otherwise, glycine has a remarkably clean safety record across decades of clinical and consumer use.

Who should be cautious

People taking clozapine should avoid high-dose glycine. Those with active liver or kidney disease should consult a clinician before taking gram-level doses. Pregnant and breastfeeding women should rely on dietary intake; supplementation safety data are limited. Anyone on multiple CNS-active medications should review the addition with a prescriber.

Interactions

Glycine may reduce the antipsychotic efficacy of clozapine through complex effects on NMDA-receptor function; this combination should be avoided or managed by a psychiatrist. Glycine has theoretical additive effects with sedatives and CNS depressants, though clinical reports of meaningful interactions are scarce. It does not interact significantly with most cardiovascular, metabolic, or antibiotic medications.

Frequently asked questions

Will glycine make me drowsy during the day?⌄

Most people don't experience daytime drowsiness from glycine, even at 3 to 5 gram doses. Its effect on sleep onset is real but subtle, and its sedative quality is much milder than melatonin or antihistamines. Many users take glycine in the morning for collagen support without issue.

Can I take glycine with collagen peptides?⌄

Yes, and it's a common combination. Collagen peptides themselves are about 22 percent glycine, so adding free glycine simply boosts the total. No absorption conflict.

How quickly does glycine work for sleep?⌄

Take it 30 to 60 minutes before bed. Trials report effects on both subjective sleep quality and objective sleep measures within the first night, but effect size is moderate. Don't expect a knockout punch.

Is glycine the same as glycerin?⌄

No. Glycine is an amino acid. Glycerin (glycerol) is a sugar alcohol used in food and skincare. Unrelated despite the similar name.

How much glycine is in bone broth?⌄

Roughly 2 to 4 grams per cup, depending on simmer time and bone-to-water ratio. That overlaps with typical supplemental doses, which is one reason traditional broths have a long history of use for joint and sleep support.

References

Wikidata: Glycine — Wikidata link
PubChem: Glycine — PubChem link

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Disclaimer: These statements have not been evaluated by the FDA. This page is educational, not a substitute for personalized medical advice. Evidence grades are AI-assisted assessments — talk to your doctor before starting any new supplement, especially if you're pregnant, breastfeeding, on medications, or managing a chronic condition.