Glycine
Best-in-class: Glycine
A simple, sweet-tasting amino acid that acts as an inhibitory neurotransmitter, a building block of collagen and glutathione, and a mild body-temperature regulator for sleep.
Glycine quick facts
| Suggested dose | 3 g before bed for sleep; higher for glutathione/metabolic goals. |
| How often | Daily |
| Who it's for | Sleep quality, glutathione support, collagen and metabolic health. |
| Best-in-class brand | Glycine |
Underrated, cheap, and it tastes sweet enough to take neat. The evidence is for sleep quality and next-day alertness rather than knocking you out — people report waking less and feeling clearer in the morning rather than falling asleep faster. Three grams about an hour before bed is the studied approach. It's also the rate-limiting amino acid for glutathione synthesis and a major component of collagen, so there's a reasonable case for it beyond sleep.
How Glycine actually works
Glycine is one of the two main inhibitory neurotransmitters — it opens chloride channels at glycine receptors, hyperpolarizing neurons and quieting them, particularly in the brainstem and spinal cord. It's also an obligatory co-agonist at NMDA receptors, so its effects aren't purely suppressive. The mechanism behind the sleep finding is more specific and more interesting than sedation: glycine promotes peripheral vasodilation, which dumps heat from the extremities and lowers core body temperature. A falling core temperature is one of the physiological triggers for sleep onset.
Where to get Glycine
Buy Glycine at Thorne →The evidence for Glycine
Graded by what exists behind each claim.
✅ Clinically validated
- RCTs show 3 g before bed improves subjective sleep quality and next-day alertness.
- A rate-limiting amino acid for glutathione and collagen synthesis.
📊 Correlative data
- Low glycine availability is associated with impaired glutathione status and metabolic strain.
🧪 Theoretical / extrapolated benefits
- The GlyNAC (glycine + NAC) longevity work is exciting but early; broad anti-aging claims outrun current human data.
How to read these tiers: they say how much human evidence exists, not how well something works — and ✗ flags harm, never a disappointing trial. How the evidence tiers work →
What Glycine actually does
Glycine is the smallest amino acid and it is conditionally essential, which is a specific claim rather than a hedge. The body synthesizes it from serine through serine hydroxymethyltransferase, and from threonine and choline by minor routes, at roughly 3 grams a day. Estimated obligatory use for collagen, glutathione, creatine, heme, purines and bile acid conjugation is closer to 12 grams. The arithmetic implies a shortfall of several grams a day on an ordinary diet, and that gap is the argument for supplementing it Ramos-Jiménez 2024.
Its largest single destination is collagen, and the reason is geometric. Every third residue of the collagen triple helix must be glycine, because only a hydrogen side chain fits in the interior of the helix. Collagen is about a third glycine by residue count and is the most abundant protein in the body, so connective tissue turnover is a continuous glycine drain.
Its second destination is glutathione, where it is the third and frequently limiting residue. Glutathione synthetase joins glycine to gamma-glutamylcysteine, and in older adults glycine availability limits that step alongside cysteine Kumar 2023.
The sleep effect is a receptor effect, and it is not sedative. Glycine is an inhibitory neurotransmitter at the strychnine-sensitive glycine receptor in brainstem and spinal cord, and a co-agonist at the NMDA receptor glycine site. The mechanism proposed for its sleep effect is peripheral vasodilation through NMDA receptors in the suprachiasmatic nucleus, lowering core body temperature — which is the physiological signal that precedes sleep onset rather than a hypnotic action.
And it is a methyl sink, which is the mechanism nobody mentions. Glycine N-methyltransferase consumes S-adenosylmethionine to make sarcosine, and it is the principal regulator of the methylation ratio in the liver. That connects glycine directly to the betaine and folate pages in this catalog, in the opposite direction.
Cell, rodent, human — and where it stops
The marker here is a self-rated sleep score or a plasma amino acid, and the more interesting human evidence is about glutathione rather than about sleep.
The biochemistry transfers without dispute. Collagen composition, glutathione synthesis and the receptor pharmacology are established, and the synthesis-versus-demand shortfall has been calculated repeatedly Ramos-Jiménez 2024.
The best-controlled human result is about glutathione, not sleep. Supplementing glycine with N-acetylcysteine in older adults improved glutathione deficiency along with oxidative stress and mitochondrial function measures Kumar 2023, and a randomized controlled trial in healthy older adults tested the same combination against glutathione repletion Lizzo 2022. Those are marker endpoints, measured properly, in the population where the deficit is real.
The sleep literature is small, old and uses questionnaires. The frequently cited 3 g before bed studies are small crossovers with subjective sleep quality and next-day fatigue as endpoints. A related and better-designed trial gave collagen peptide — which is largely glycine, proline and hydroxyproline — before bedtime and reported reduced sleep fragmentation and improved cognitive function using objective measures in physically active males with sleep complaints Thomas 2023.
The obstacle to transfer is that collagen peptide is not glycine. A collagen amino acid composition has been tested for effects on biological age markers Dakhovnik 2025, and every one of those studies delivers a mixture in which glycine is a third of the residues and never the only variable. Attributing the result to glycine is an assumption.
And the performance literature is honest about where it stands. The update on glycine for enhancing physical performance and recovery describes a promise rather than a demonstration, with the mechanistic case ahead of the trial evidence Ramos-Jiménez 2024.
Glycine — which form, and does it matter
There is one molecule and the form questions are about what it is delivered with. Glycine powder is the free amino acid and is sweet, cheap and completely soluble. Magnesium glycinate delivers roughly 1.4 g of glycine per 200 mg of elemental magnesium, which is a meaningful glycine dose arriving under another product's name. Collagen peptide delivers glycine as part of a mixture Thomas 2023.
Absorption is complete and unremarkable, which is unusual enough to state. Glycine is absorbed by sodium-dependent amino acid transporters and by PepT1 as di- and tripeptides, with oral bioavailability close to complete at supplemental doses. Peak plasma concentration arrives at roughly 30 to 60 minutes and the plasma half-life is short, well under 2 hours, because the amino acid is either used or deaminated. There is no cytochrome step and no meaningful first-pass barrier — the liver takes it up and uses it, which is the destination rather than an obstacle.
The two disposal routes are what limit a large dose. The glycine cleavage system in the mitochondrion, a thiamine-independent complex requiring pyridoxal 5'-phosphate and tetrahydrofolate, degrades glycine and feeds a methylene group into the folate cycle; and glycine N-methyltransferase consumes S-adenosylmethionine. Both connect a large glycine dose to the one-carbon pages in this catalog.
The dose gap between the sleep studies and the metabolic ones is large. Sleep work uses 3 g at bedtime. The glutathione work uses roughly 100 mg per kilogram per day, which is 7 to 8 g for most adults, alongside N-acetylcysteine Kumar 2023. Those are different interventions and a 3 g capsule reproduces only the first one.
What no form changes. Glycine is sweet, so a large powder dose is palatable in water, and the cost per gram is among the lowest in this catalog. A collagen product delivering the same glycine costs several times as much and carries the additional amino acids, which is either the point or the markup depending on which claim is being bought Dakhovnik 2025.
What would have to be true, and how you would know it was not
1. Predict the objective sleep measure is where the claim stands or falls. On 3 g at bedtime, predict an improvement in self-rated sleep quality and predict a much smaller change on actigraphy or a polysomnograph Thomas 2023. Measure both for two weeks on and two weeks off.
2. Predict core body temperature falls slightly before sleep onset. The proposed mechanism is peripheral vasodilation and a faster nocturnal temperature decline. Predict a measurable drop in distal-to-proximal skin temperature gradient within an hour of a 3 g dose, which is the mechanism test rather than the outcome test.
3. The prediction that cuts against the product. Predict that glycine alone, without cysteine, does not raise erythrocyte glutathione, because both substrates are limiting in the population where the deficit exists Kumar 2023 Lizzo 2022. A trial of glycine alone raising glutathione would falsify the reasoning here.
4. Predict the collagen claim cannot be attributed to glycine. Predict that a trial comparing collagen peptide against an equal glycine dose finds a difference, because collagen delivers proline, hydroxyproline and specific di- and tripeptides that free glycine does not Thomas 2023 Dakhovnik 2025. Nobody has run that comparison.
5. Predict a homocysteine effect at large doses and check it. Because glycine N-methyltransferase consumes S-adenosylmethionine, predict that 7 to 10 g a day measurably shifts one-carbon metabolism. Measure homocysteine at baseline and at 12 weeks on a high dose; either direction of movement is informative and nobody has published it.
What nobody has tested yet
Nobody has isolated glycine from collagen in a trial. The sleep and connective tissue literature runs on collagen peptides Thomas 2023 Dakhovnik 2025 and the amino acid is available as a cheap powder. A three-arm trial — collagen, matched glycine, placebo — is the obvious missing study.
The conditional-shortfall calculation has never been tested directly. The estimate that ordinary diets leave a several-gram glycine deficit is an arithmetic argument Ramos-Jiménez 2024. Whether a functional consequence follows has never been demonstrated with a stable isotope study of collagen or glutathione synthesis rate at different intakes.
The sleep mechanism has not been confirmed in a human. The temperature hypothesis is plausible and has not been tested with simultaneous core temperature and polysomnography in an adequately sized trial Barnard 2022.
And the high-dose methylation question is open. Glycine N-methyltransferase is a major consumer of S-adenosylmethionine and nobody has measured the methylation consequences of chronic 10 g dosing in people. That is a straightforward biomarker study and it would inform every methylation stack that contains glycinate salts.
Glycine — its own safety story, not its category's
Glycine is among the best-tolerated substances in this catalog and the reason is that it is an ordinary dietary component. Doses up to 15 g a day have been used in trials with mild gastrointestinal upset the only common complaint Ramos-Jiménez 2024. There is no established tolerable upper intake level.
The one setting where it needs care is renal, and it is mechanistic. Glycine is nitrogen-containing and is deaminated to urea; a large chronic dose adds to nitrogen load. In advanced chronic kidney disease that is a reason to raise it with a clinician rather than assume an amino acid is inert.
The interaction that is easiest to overlook is with clozapine. Glycine acts at the NMDA receptor glycine site, and high-dose glycine has been reported to reduce clozapine efficacy in schizophrenia. That is a pharmacodynamic interaction with a specific mechanism rather than a theoretical one.
Two things people expect and should not. Glycine is sweet and is used as a sweetener, so a large dose in a drink is palatable and easy to overshoot. And a magnesium glycinate product is already delivering grams of glycine, so stacking one with a glycine powder is a larger dose than either label suggests.
Who should check first. Anyone with reduced kidney function; anyone on clozapine; and anyone pregnant or breastfeeding at supplemental doses, where there are no data. Beyond that this is a cheap amino acid with a plausible mechanism, a thin trial base and an unusually good safety record Ramos-Jiménez 2024. Nothing here is medical advice or diagnosis, and these statements have not been evaluated by the Food and Drug Administration.
Sources read for this page
- Ramos-Jiménez A. An Update of the Promise of Glycine Supplementation for Enhancing Physical Performance and Recovery. Sports (Basel) 2024 · PMID 39453231
- Thomas C. Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints. Eur J Nutr 2023 · PMID 37874350
- Dakhovnik A. A collagen amino acid composition supplementation reduces biological age in humans and increases health and lifespan in vivo. NPJ Aging 2025 · PMID 41266379
- Kumar P. Supplementing Glycine and N-Acetylcysteine (GlyNAC) in Older Adults Improves Glutathione Deficiency, Oxidative Stress, Mitochondrial Dysfunction, Inflammation, Physical Function, and Aging Hallmarks: A Randomized Clinical Trial. Journals of Gerontology Series A 2023 · PMID 35975308
- Lizzo G, et al. A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage. Frontiers in Aging 2022 · PMID 35821844
- Barnard J. The Impact of Dietary Factors on the Sleep of Athletically Trained Populations: A Systematic Review. Nutrients 2022 · PMID 36014779
How you would know if it worked
These are the markers that recommend this product on their own pages, so they are the ones that should move if it is doing what it is sold for.
- Homocysteine — Leafy greens and legumes (folate), animal proteins (B12), and adequate protein for glycine/betaine pathways Retest: 8–12 weeks after starting B vitamins.
- GGT (Gamma-Glutamyl Transferase) — Glycine 3–5 g is the other half Retest: 6 weeks minimum after any change, because of the 2–3 week half-life. Sooner than that and you are measuring the previous month. Every 6–12 months as routine if you drink, carry visceral fat, or run oral compounds.
Draw before you start, not after. A result with nothing to compare it to answers nothing.
Glycine — safety & side effects
- Very well tolerated. Soft stools and mild nausea at doses above about 15 g.
- No established toxicity or significant drug interactions.
- Caution with clozapine — glycine may reduce its effectiveness. Otherwise one of the genuinely benign options for sleep.
Not medical advice. If you take prescription medication or have a diagnosed condition, check this against it with a pharmacist or doctor — pharmacists are underused and free.
Build your foundation with Coach Cam
The full Supplement Vault — 371 products across 14 categories with clinical, correlative & theoretical evidence, plus my Thorne partner links — lives inside Skool alongside 278 peptides.
Join Skool — $10/mo →Bloodwork to run alongside Glycine
Baseline first, then again at 8–12 weeks.
| Marker | What it’s watching for |
|---|---|
| TSH (Thyroid-Stimulating Hormone) | Thyroid disease disrupts sleep in both directions |
| Ferritin | Low iron drives restless legs, a common hidden cause |
| Vitamin D (25-Hydroxy) | Associated with sleep quality and commonly low |
| Magnesium, RBC | The form worth measuring if you're dosing magnesium |
The Sleep Quality & Recovery panel covers these in one order — 11 markers, $172.35 with the discount applied.
Check results you already have → · All 103 markers A–Z
Glycine — frequently asked questions
What is Glycine?
A simple, sweet-tasting amino acid that acts as an inhibitory neurotransmitter, a building block of collagen and glutathione, and a mild body-temperature regulator for sleep.
What is the suggested dose of Glycine?
3 g before bed for sleep; higher for glutathione/metabolic goals. This is a general reference for education only — statements have not been evaluated by the FDA and this is not medical advice.
What are the researched benefits of Glycine?
RCTs show 3 g before bed improves subjective sleep quality and next-day alertness.
Who is Glycine for?
Sleep quality, glutathione support, collagen and metabolic health.
Where can I buy Glycine?
Coach Cam sources Glycine from Thorne, with 10% off auto-applied at checkout — use the buy link on this page.
Glycine inside a finished plan
One arm of 5 Protocol Blueprints, free to read in full.
What Glycine is used for
Glycine appears under 5 goals in the goal router.
Related Sleep supplements
Where this goes next
Glycine is the recovery & sleep arm of this plan. The page above is the free breakdown of one compound; the plan it belongs to — the dosing, the order to correct things in, the week-by-week schedule and what to retest — is a lesson inside Skool.