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Glycine
Glycine is a non-essential amino acid that functions as an inhibitory neurotransmitter in the central nervous system, particularly in the brainstem and spinal cord.
- Evidence
- Likely Effective
- Category
- Sleep & Relaxation
- Best form
- Pure glycine powder (most cost-effective, dissolves easily)
- Effective dose
- 3g (3,000mg) taken 30-60 minutes before bed, dissolved in water or taken as capsules
- Lab tested
- 5 of 8 products
- Category
- Sleep & Relaxation
- Best form
- Pure glycine powder (most cost-effective, dissolves easily)
- Effective dose
- 3g (3,000mg) taken 30-60 minutes before bed, dissolved in water or taken as capsules
- Lab tested
- 5 of 8 products
Key takeaways
- →3g before bed has moderate evidence for better subjective sleep quality, faster onset, and less next-day fatigue (Yamadera 2007, Inagawa 2006, Bannai 2012). Effect size is modest but safety is excellent.
- →Effective dose is 3g, not the 500-1,000mg in most capsules. Reaching 3g via capsules means 5-6 pills - powder is the practical form at $0.05-0.15 per effective dose.
- →Works by dropping core body temperature via peripheral vasodilation, a natural sleep signal. Unlike melatonin, it does not shift the circadian clock, cause morning grogginess, or show receptor adaptation.
- →Not a first-line insomnia treatment - trials were in healthy adults with mild complaints, not insomnia disorder. CBT-I is first-line for chronic insomnia. Best positioned as a low-side-effect alternative to melatonin.
What Is Glycine?
Glycine is a non-essential amino acid that functions as an inhibitory neurotransmitter in the central nervous system, particularly in the brainstem and spinal cord. It is also a co-agonist at NMDA receptors and appears to lower core body temperature when taken before bed - a physiological signal that precedes sleep onset. These mechanisms are the proposed basis for its sleep-related effects.
The best human evidence comes from a small group of randomized, placebo-controlled trials conducted by Japanese researchers between 2006 and 2012. In Yamadera et al. 2007, 3g of glycine before bed improved subjective sleep quality and reduced sleep onset latency in adults with mild sleep complaints. Bannai and Kawai's 2012 review of the research program summarized consistent findings: improved satisfaction with sleep, reduced daytime sleepiness, and reduced fatigue after partial sleep deprivation. Polysomnography in one study showed shortened time to slow-wave sleep without altering total sleep architecture.
The evidence base is smaller than for melatonin or magnesium. Most trials enrolled 15-30 participants, were conducted by the same research group, and focused on self-reported outcomes rather than clinical insomnia. No large independent replication has been published. That said, the mechanism is plausible, the dose is consistent across studies (3g), safety at this dose is well-established, and no trials have found adverse sleep effects.
Glycine has additional research in areas outside sleep - schizophrenia adjunct therapy (at much higher doses of 30-60g), ischemic stroke, and collagen synthesis support - but these are beyond the scope of a sleep-focused supplement scorecard and involve doses unsafe or impractical for general use.
The practical positioning: glycine is worth trying if you want a low-side-effect sleep aid, if melatonin makes you groggy, or if you want something you can take nightly without concerns about receptor adaptation. It is not a first-line choice if you have chronic insomnia - that calls for CBT-I - and the effect size on objective sleep metrics is modest. The product market is refreshingly simple: glycine is cheap, chemically stable, and hard to mislabel, so most brands deliver what they claim.
Does It Work? The Evidence
Improved subjective sleep quality
SupportedYamadera et al. 2007 (n=19, crossover RCT): 3g glycine before bed significantly improved subjective sleep quality scores vs. placebo; Bannai & Kawai 2012 review summarizes consistent findings across 4 small Japanese RCTs
Reduced sleep onset latency (falling asleep faster)
SupportedYamadera et al. 2007: polysomnography showed shortened time to slow-wave sleep; Inagawa et al. 2006 (n=15): 3g reduced subjective time-to-sleep on self-report sleep diaries
Reduced next-day fatigue and sleepiness after partial sleep restriction
SupportedInagawa et al. 2006: in a partial sleep deprivation protocol (25% sleep reduction for 3 nights), 3g glycine before bed reduced self-reported fatigue and daytime sleepiness vs. placebo
Next-day cognitive performance after sleep restriction
Early SignalBannai et al. 2012 (n=10): 3g glycine showed modest improvement in psychomotor vigilance after sleep restriction; small sample limits confidence in the magnitude of effect
Treatment of clinical insomnia
Not There YetExisting RCTs enrolled healthy adults with mild sleep complaints, not patients diagnosed with insomnia disorder; no large trials in clinical insomnia populations have been published
Reduced core body temperature as a sleep mechanism
SupportedKawai et al. 2015 (rat model and human pilot data): glycine lowered core body temperature via peripheral vasodilation - a plausible mechanism since body temperature drop precedes natural sleep onset
Schizophrenia symptom adjunct (high-dose context)
Not There YetAt doses of 30-60g (10-20x typical sleep dose), glycine has been studied as an adjunct for negative symptoms of schizophrenia via NMDA modulation; irrelevant to sleep use but noted for context
| Claimed Benefit | Key Studies | Our Verdict |
|---|---|---|
| Improved subjective sleep quality | Yamadera et al. 2007 (n=19, crossover RCT): 3g glycine before bed significantly improved subjective sleep quality scores vs. placebo; Bannai & Kawai 2012 review summarizes consistent findings across 4 small Japanese RCTs | Supported |
| Reduced sleep onset latency (falling asleep faster) | Yamadera et al. 2007: polysomnography showed shortened time to slow-wave sleep; Inagawa et al. 2006 (n=15): 3g reduced subjective time-to-sleep on self-report sleep diaries | Supported |
| Reduced next-day fatigue and sleepiness after partial sleep restriction | Inagawa et al. 2006: in a partial sleep deprivation protocol (25% sleep reduction for 3 nights), 3g glycine before bed reduced self-reported fatigue and daytime sleepiness vs. placebo | Supported |
| Next-day cognitive performance after sleep restriction | Bannai et al. 2012 (n=10): 3g glycine showed modest improvement in psychomotor vigilance after sleep restriction; small sample limits confidence in the magnitude of effect | Early Signal |
| Treatment of clinical insomnia | Existing RCTs enrolled healthy adults with mild sleep complaints, not patients diagnosed with insomnia disorder; no large trials in clinical insomnia populations have been published | Not There Yet |
| Reduced core body temperature as a sleep mechanism | Kawai et al. 2015 (rat model and human pilot data): glycine lowered core body temperature via peripheral vasodilation - a plausible mechanism since body temperature drop precedes natural sleep onset | Supported |
| Schizophrenia symptom adjunct (high-dose context) | At doses of 30-60g (10-20x typical sleep dose), glycine has been studied as an adjunct for negative symptoms of schizophrenia via NMDA modulation; irrelevant to sleep use but noted for context | Not There Yet |
How to Choose: Forms, Doses & What Matters
Clinical dose: 3g (3,000mg) taken 30-60 minutes before bed, dissolved in water or taken as capsules
Best forms: Pure glycine powder (most cost-effective, dissolves easily), Capsules (convenience, but reaching 3g requires 5-6 capsules)
Take 3g (approximately 1 teaspoon of powder or 5-6 capsules depending on product) 30-60 minutes before bed. Powder dissolves easily in water or a small amount of juice - glycine has a mildly sweet taste and is more palatable than most amino acids. Consistency matters more than exact timing: take it at approximately the same time each night. Glycine does not require co-factors or particular timing relative to food, though taking it on an empty or light stomach may shorten onset of any subjective effect. Unlike melatonin, glycine can be taken later if you forget - there is no narrow circadian timing window to hit. Stacking with magnesium glycinate or L-theanine is reasonable and there are no documented negative interactions.
Who Should Take Glycine?
Adults with mild sleep complaints who want a low-side-effect option. People who find melatonin causes next-day grogginess or vivid dreams. Those who want a sleep aid they can take nightly without concern about receptor adaptation or rebound effects. People looking for a supplement they can stack with other sleep supports (magnesium, L-theanine) without interaction concerns. The evidence is strongest for improving subjective sleep quality in people who fall asleep eventually but feel their sleep is not restful - not people with severe insomnia or those who wake repeatedly through the night.
Who Should Avoid It?
People with clozapine prescriptions should not take glycine - it can reduce clozapine efficacy through NMDA receptor interactions. Those on NMDA-modulating medications should consult their prescriber. Pregnant or breastfeeding women lack adequate safety data for supplemental glycine at 3g doses. People with liver or kidney disease should use caution and consult a clinician, as the body must clear amino acid loads. Anyone with a diagnosed sleep disorder (insomnia disorder, sleep apnea, restless legs syndrome) should be evaluated medically first - glycine is not a substitute for diagnosis and evidence-based treatment of these conditions.
Side Effects & Safety
Glycine at 3-5g before bed is well-tolerated in healthy adults with no common or serious adverse effects reported in published trials. Mild gastrointestinal discomfort (soft stools, mild nausea) is the most frequently reported issue, typically resolved by taking with a small amount of food or splitting the dose. Single doses up to 9g have been used in research without serious adverse events. There is no evidence of dependence, tolerance, or withdrawal. Glycine is not a CNS depressant in the manner of benzodiazepines and does not impair next-day cognitive function - in fact, multiple trials have shown the opposite after sleep restriction. Long-term safety data at nightly 3g doses extends to several months of continuous use in research settings; longer-term data is limited but no mechanistic concerns are established.
Product Scores
8 products scored on dosing accuracy, third-party testing, cost per effective dose, and label transparency.
The Scorecard: 8 Products Compared
Glycine Powder (pure)
NOW FoodsThe practical default for glycine. Cheap, clean label, easy to dose accurately at the research-backed 3g, widely available. No meaningful reason to pay more for glycine unless you specifically need a capsule format or a premium brand certification.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine Powder
BulkSupplements
The lowest cost per effective dose we could verify. Bare-bones branding and packaging keeps the price down. A good choice if you are committed to nightly glycine and want to minimize cost.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine
ThorneBest for people with allergies or sensitivities who want a practitioner-grade brand. Note the practical issue: reaching 3g requires 6 capsules nightly, which makes this an expensive way to take glycine. Powder is the more sensible form.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine 1000mg
Life ExtensionA solid capsule option with a 1g dose that makes reaching the research-backed 3g more practical than 500mg alternatives. Third-party testing is a meaningful advantage over lower-priced capsule brands.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine Powder
Source Naturals
A reasonable second-tier powder option. No strong reason to choose this over NOW Foods unless availability is an issue or you prefer the brand.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine
Pure EncapsulationsThe capsule format and premium pricing make this a niche choice - justified mainly for people with multiple sensitivities to powdered product excipients. For most buyers, NOW or BulkSupplements powder is the better value.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine
Jarrow FormulasThe best capsule choice for people who cannot use powder. The 1g-per-capsule dose is the most practical capsule format we found - three capsules is a manageable nightly serving.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Glycine 500mg
SolgarRepresents a common problem in the glycine capsule market: the 1-2 capsule serving size produces 500-1000mg, which is well below the 3g needed for research-documented sleep effects. If you buy this, plan on 6 capsules per serving - and consider powder instead.
Prices checked 2026-04-14. Cost shown is per clinically effective daily dose, not per pill.
Full Comparison
| Category | Glycine Powder (pure) NOW Foods | Glycine Powder BulkSupplements | Glycine Thorne | Glycine 1000mg Life Extension | Glycine Powder Source Naturals | Glycine Pure Encapsulations | Glycine Jarrow Formulas | Glycine 500mg Solgar |
|---|---|---|---|---|---|---|---|---|
| Brand Score | 90/100Winner | 87/100 | 85/100 | 83/100 | 82/100 | 82/100 | 80/100 | 72/100 |
| Dosing & Form | 25/25Winner | 25/25 | 22/25 | 23/25 | 25/25 | 22/25 | 22/25 | 18/25 |
| Purity | 20/25 | 19/25 | 24/25Winner | 19/25 | 17/25 | 22/25 | 17/25 | 18/25 |
| Value | 24/25Winner | 24/25 | 17/25 | 20/25 | 21/25 | 15/25 | 21/25 | 14/25 |
| Transparency | 21/25 | 19/25 | 22/25 | 21/25 | 19/25 | 23/25Winner | 20/25 | 22/25 |
| Cost/Day | $0.08 | $0.06Winner | $0.35 | $0.25 | $0.12 | $0.48 | $0.22 | $0.51 |
| Dose/Serving | 3g | 3g | 0.5g | 1g | 3g | 0.5g | 1g | 0.5g |
| Form | Pure powder | Pure powder | Capsule | Capsule | Pure powder | Capsule | Capsule | Capsule |
| Third-Party Tested | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | No | ✓ Yes | No | No |
| Proprietary Blend | No | No | No | No | No | No | No | No |
Frequently Asked Questions
How is glycine different from melatonin for sleep?
Melatonin signals circadian timing - it tells the body it is night. It works best for jet lag, shift work, and delayed sleep phase. Glycine does not shift the circadian clock. It works through inhibitory neurotransmission and by lowering core body temperature, which is a separate physiological pathway to sleep onset. Practically: melatonin is the right choice for circadian problems, glycine is worth trying for general subjective sleep quality, and the two can be taken together. Glycine is also less likely to cause next-morning grogginess at typical doses.
Why is the effective dose 3g when most capsules contain 500mg?
This is a mismatch between the product market and the research. All published positive trials used 3g (3,000mg) before bed. A 500mg capsule delivers one-sixth of that dose. You would need to take 5-6 capsules per night to reach the research-supported dose, which makes capsule-form glycine awkward and expensive. Powder is the more practical form: a 1/2 to 1 teaspoon scoop delivers 3g, dissolves in water, and costs a fraction of the equivalent capsule dose. If you buy capsules, check the label carefully and plan on multiple capsules per serving.
Can I take glycine every night?
Yes, based on available evidence. Glycine does not appear to cause tolerance, dependence, or rebound insomnia on discontinuation. It is an amino acid the body produces and uses normally, not a drug acting on unique receptors that might down-regulate. Research has used nightly 3g for weeks to months without issue. That said, if you find you need a sleep aid every night indefinitely, the underlying sleep problem is worth addressing - CBT-I is the evidence-based first-line treatment for chronic insomnia and produces longer-lasting results than any supplement.
Does glycine make you groggy the next morning?
At the 3g research dose, next-morning grogginess is uncommon. This is one of the practical advantages over melatonin (where grogginess increases with doses above 3mg) and sedative-hypnotic drugs. In fact, a trial by Inagawa et al. found that glycine before bed reduced next-day fatigue after partial sleep restriction compared to placebo. If you do experience grogginess, you are either taking too much (try splitting the dose) or are responding idiosyncratically, which is rare.
Can I stack glycine with magnesium or L-theanine?
Yes. There are no documented negative interactions between glycine and other common sleep supports like magnesium glycinate, L-theanine, or low-dose melatonin. Many people find this combination works better than any single ingredient. Magnesium glycinate actually contains glycine bound to magnesium, so some practitioners recommend a dedicated glycine dose separately to reach the research-backed 3g amount, since the glycine content of magnesium glycinate alone is typically well below 3g at standard doses.
What should I look for when buying glycine?
Glycine is one of the simpler supplements to buy well. The ingredient is chemically stable, easy to test, and inexpensive to manufacture, so most brands deliver what they claim. Look for: pure glycine with no added ingredients (unless you specifically want a sleep blend), powder form for cost-effectiveness, third-party testing or GMP certification, and a pharmaceutical-grade or USP-grade designation. Brand premium pricing is not well-justified for glycine as it is for more complex ingredients - good-value bulk powder from a reputable brand is a reasonable default.
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Sources
- Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms. 2007;5(2):126-131.
- Inagawa K, Hiraoka T, Kohda T, Yamadera W, Takahashi M. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep and Biological Rhythms. 2006;4(1):75-77.
- Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci. 2012;118(2):145-148.
- Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012;3:61.
- Kawai N, Sakai N, Okuro M, et al. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology. 2015;40(6):1405-1416.
- File SE, Fluck E, Fernandes C. Beneficial effects of glycine (bioglycin) on memory and attention in young and middle-aged adults. J Clin Psychopharmacol. 1999;19(6):506-512.
- NIH U.S. National Library of Medicine. Glycine - MedlinePlus Supplement Information.
- Razak MA, Begum PS, Viswanath B, Rajagopal S. Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review. Oxid Med Cell Longev. 2017;2017:1716701.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. The products discussed on this page are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.