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Glycine
Bottom line
In our scoring, Glycine rates likely effective: the research is fairly solid for subjective sleep quality. Our top-scored product is Glycine Powder (pure) (89/100), about $0.12 a day at a clinical dose of 3g. Bottom line: a reasonable pick if it fits your goal. This is our opinion, not medical advice; talk to your clinician before starting.
Glycine at 3g before bed is worth trying if melatonin leaves you groggy or you want a sleep aid you can take nightly without worrying about tolerance.
- 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
- 6 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
- 6 of 8 products
Key takeaways
- →Modest evidence for better subjective sleep quality and less next-day fatigue - works by dropping core body temperature, not by sedation.
- →Take 3g before bed, not the 500-1,000mg in most capsules; powder is the practical form since 3g requires 5-6 pills.
- →NOW Foods Glycine Powder ($0.12/day) is the top pick; Source Naturals ($0.07/day) is the current value option after a steep price drop.
- →Not a first-line treatment for diagnosed insomnia disorder - CBT-I comes first. Avoid combining with clozapine.
What Is Glycine?
Glycine at 3g before bed is worth trying if melatonin leaves you groggy or you want a sleep aid you can take nightly without worrying about tolerance. Small Japanese RCTs consistently show better subjective sleep quality, faster onset to slow-wave sleep, and less next-day fatigue at this dose, modest effects, but the mechanism (lowering core body temperature) is plausible and safety at 3g is well established. The evidence base is smaller than for melatonin or magnesium, and this is not a treatment for diagnosed insomnia. But the effect is real, side effects are minimal, and the product market is simple enough that most brands deliver what they claim.
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
How A-F grades workGlycine earns a Likely Effective rating on the strength of its best-supported uses: improved subjective sleep quality and reduced sleep onset latency (falling asleep faster) (grade B). The table below grades every claimed benefit on its own, including weaker and more heavily marketed uses, so one strong result never stands in for the rest.
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
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
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
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
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
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
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
| Grade | Claimed Benefit | Key Studies | Our Verdict |
|---|---|---|---|
| B | 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 |
| B | 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 |
| B | 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 |
| B | 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 |
| B | 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 |
| C | 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 |
| C | 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 |
Glycine Dosage: How Much to Take
Glycine dosage, in one line: the evidence-supported range is 3g (3,000mg) taken 30-60 minutes before bed, dissolved in water or taken as capsules.
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?
Not for everyone
Side Effects & Safety
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 Foods$17.40 ÷ 145 days at 3g/day (1 serving × 3g)
The 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 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Glycine Powder
BulkSupplements
$32.97 ÷ 330 days at 3g/day (1 serving × 3g)
Long the lowest cost per effective dose here, but the 2026 price rise hands that title to Source Naturals for now. Bare-bones branding and packaging still keeps the per-gram price low for a 1kg commitment.
Prices checked 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Glycine Powder
Source Naturals
$8.24 ÷ 118 days at 3g/day (1 serving × 3g)
At the current $8.24 Buy Box this is the cheapest verified glycine per dose in our comparison - a reversal of its usual second-tier pricing. The lack of any product-level third-party testing is the trade-off versus NOW or BulkSupplements.
Prices checked 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Glycine 1000mg
Life Extension$12.00 ÷ 33 days at 3g/day (3 servings × 1g)
A 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 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Glycine
Thorne$31.00 ÷ 42 days at 3g/day (6 servings × 0.5g)
Best 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 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
NOW Foods Glycine 1,000 mg
NOW Foods$11.00 ÷ 33 days at 3g/day (3 servings × 1g)
The 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 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Glycine
Pure Encapsulations$35.00 ÷ 30 days at 3g/day (6 servings × 0.5g)
The 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 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Glycine 500mg
Solgar$11.00 ÷ 17 days at 3g/day (6 servings × 0.5g)
Represents 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 2026-06-11. Cost shown is per clinically effective daily dose, not per pill.
Full Comparison
| Category | Glycine Powder (pure) NOW Foods | Glycine Powder BulkSupplements | Glycine Powder Source Naturals | Glycine 1000mg Life Extension | Glycine Thorne | NOW Foods Glycine 1,000 mg NOW Foods | Glycine Pure Encapsulations | Glycine 500mg Solgar |
|---|---|---|---|---|---|---|---|---|
| Brand Score | 89/100Winner | 86/100 | 84/100 | 83/100 | 81/100 | 79/100 | 78/100 | 73/100 |
| Dosing & Form | 25/25Winner | 25/25 | 25/25 | 23/25 | 22/25 | 22/25 | 22/25 | 18/25 |
| Purity | 20/25 | 19/25 | 17/25 | 19/25 | 24/25Winner | 17/25 | 22/25 | 18/25 |
| Value | 23/25Winner | 23/25 | 23/25 | 20/25 | 13/25 | 20/25 | 11/25 | 15/25 |
| Transparency | 21/25 | 19/25 | 19/25 | 21/25 | 22/25 | 20/25 | 23/25Winner | 22/25 |
| Cost/Day | $0.12 | $0.10 | $0.07Winner | $0.36 | $0.74 | $0.33 | $1.17 | $0.66 |
| Dose/Serving | 3g | 3g | 3g | 1g | 0.5g | 1g | 0.5g | 0.5g |
| Form | Pure powder | Pure powder | Pure powder | Capsule | Capsule | free-form glycine capsule | Capsule | Capsule |
| Third-Party Tested | ✓ Yes | ✓ Yes | No | ✓ Yes | ✓ Yes | ✓ Yes | ✓ Yes | 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.
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.
Scores and tiers are our independent opinion, formed by applying a published rubric to label data, third-party certifications, and the research record. They are not statements of objective fact about a product and not a lab test. Where we report a brand-specific fact, it comes from a cited source or a public certification; where verification is missing, we say so rather than assume a result.
FDA Disclaimer: These statements have not been evaluated by the Food and Drug Administration. Dietary supplements are not intended to diagnose, treat, cure, or prevent any disease. Always consult with a qualified healthcare professional before starting any supplement regimen.