Glycine is an amino acid that improves sleep quality by lowering core body temperature — a different mechanism than melatonin. Clinical studies show 3g before bed reduces time to fall asleep, improves sleep quality, and decreases next-day fatigue. Our top pick is BulkSupplements Glycine Powder for its pure, affordable formula.
How We Picked
We evaluated glycine supplements on purity (should be USP or pharmaceutical-grade glycine with no unnecessary additives), dose per serving (clinical studies use 3g), form (powder vs. capsule — powder is more practical at 3g doses), third-party testing, and cost per serving.
A. BulkSupplements Glycine Powder — Best Overall
BulkSupplements Glycine Powder
BulkSupplements
- Pure glycine powder — no fillers, no additives
- 3g per serving (matches clinical study dose exactly)
- Third-party tested for purity and heavy metals
- Mildly sweet taste — dissolves easily in water
- 500g bag — over 166 servings
Why we picked it: BulkSupplements delivers exactly what you need: pure glycine at the clinical dose (3g), nothing else. At 166+ servings per bag, the cost per serving is pennies. Glycine has a naturally mild, slightly sweet taste that's pleasant in water — no need for flavoring. The powder form is practical since the clinical dose of 3g would require 4–6 capsules in most encapsulated products.
B. NOW Foods Glycine 1000mg Capsules — Best Capsule Form
NOW Foods Glycine 1000mg Capsules
NOW Foods
- 1,000mg glycine per capsule (take 3 for clinical dose)
- Pharmaceutical grade (USP) glycine
- Free-form amino acid for rapid absorption
- GMP certified facility
- 100 veggie capsules per bottle
Why we picked it: If you prefer capsules over powder, NOW Foods offers pharmaceutical-grade glycine at 1,000mg per capsule. Take 3 capsules before bed to reach the 3g clinical dose. The free-form amino acid is rapidly absorbed without needing digestion. GMP certification and NOW's long track record make this a reliable choice for capsule users.
C. Thorne Glycine — Premium Pick
Thorne Glycine
Thorne
- Pure glycine powder — pharmaceutical grade
- Thorne's rigorous third-party testing protocols
- NSF Certified for Sport
- Dissolves easily — slightly sweet taste
- 250g container per bottle
Why we picked it: Thorne is the gold standard in practitioner-grade supplements. Their glycine meets pharmaceutical purity standards with industry-leading third-party testing for contaminants, heavy metals, and microbiological safety. NSF Certified for Sport if you need banned substance testing. Best for people who want the most trusted name in supplement quality.
What Is Glycine and How Does It Help Sleep?
What is glycine? Glycine is the simplest amino acid — a building block of protein found in bone broth, meat, fish, and legumes. Beyond its structural role, glycine acts as an inhibitory neurotransmitter in the brain and spinal cord. It's involved in hundreds of metabolic processes, including collagen synthesis, glutathione production, and — relevant here — thermoregulation.
How does it improve sleep? Glycine works by a unique mechanism: it lowers core body temperature by increasing blood flow to the extremities (peripheral vasodilation). Your body naturally needs to drop its core temperature by 1–2°F to initiate sleep. Glycine accelerates this process. It also acts on NMDA receptors in the suprachiasmatic nucleus (the brain's master clock), promoting the transition to sleep.
Why it's different from melatonin: Melatonin is a hormone that signals "darkness" to your circadian clock. Glycine works through temperature regulation and neurotransmitter activity — a completely different pathway. This makes it an excellent alternative for people who don't respond to melatonin, experience melatonin grogginess, or want to use both together for complementary effects.
Who Should Try Glycine for Sleep?
Who benefits most? People who have trouble falling asleep (glycine reduces sleep onset latency), anyone who wakes up feeling unrefreshed despite sleeping 7–8 hours (glycine improves sleep quality and reduces next-day fatigue), people who run hot at night (glycine's cooling effect is especially helpful), those who want a non-hormonal sleep supplement, and people who get melatonin "hangovers" (morning grogginess).
Who else may benefit? Glycine also supports detoxification (it's a precursor to glutathione, the body's master antioxidant), joint health (it's a major component of collagen), and may have anti-aging properties (glycine supplementation extended lifespan in multiple animal models).
When and How to Take Glycine for Sleep
When to take it: Take 3g of glycine 30–60 minutes before bed. It absorbs rapidly and reaches peak blood levels within 30 minutes. The temperature-lowering effect begins shortly after and supports the natural pre-sleep temperature drop.
Can you combine it with melatonin? Yes — glycine and melatonin work through different mechanisms and are safe to combine. Melatonin signals your circadian clock while glycine lowers temperature and provides neurotransmitter support. Together, they address two different aspects of sleep initiation. If using both, try 0.5–1mg melatonin (low-dose) + 3g glycine.
Frequently Asked Questions
How much glycine should I take for sleep?
The clinical dose is 3 grams (3,000 mg) taken 30–60 minutes before bed. This is the dose used in the landmark Japanese sleep studies that showed improved sleep quality, reduced time to fall asleep, and less next-day fatigue. Some people find benefit at 2g, but 3g is the most supported dose.
Does glycine cause any side effects?
Glycine is extremely well-tolerated — it's a naturally occurring amino acid your body already produces. Side effects are rare even at high doses. Some people report mild GI effects (soft stools) at doses above 5g. There are no known drug interactions at sleep-supportive doses. It's non-habit-forming and doesn't cause next-day drowsiness.
Can I get enough glycine from food instead of supplements?
Glycine-rich foods include bone broth (about 3g per cup — the clinical dose in one serving), gelatin, meat (especially connective tissue and skin), fish, and legumes. If you regularly consume bone broth, you may get enough glycine from diet. However, most modern diets are low in glycine because we eat muscle meat rather than the whole animal. A 3g supplement fills this gap efficiently.
Quick Comparison
| Product | Key Feature | Best For |
|---|---|---|
| BulkSupplements Glycine Powder | Pure glycine powder — no fillers, no additives | Best Overall |
| NOW Foods Glycine 1000mg Capsules | 1,000mg glycine per capsule (take 3 for clinical dose) | Best Capsule Form |
| Thorne Glycine | Pure glycine powder — pharmaceutical grade | Premium Pick |
Bottom Line: Which Should You Buy?
For most people: the BulkSupplements Glycine Powder. Pure glycine powder — no fillers, no additives.
Runner-up: the NOW Foods Glycine 1000mg Capsules. 1,000mg glycine per capsule (take 3 for clinical dose).
Also great: the Thorne Glycine. Pure glycine powder — pharmaceutical grade.
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Sources & Research
This article was informed by peer-reviewed research and clinical guidelines. The Supplements Corner Editorial Team reviews published literature to ensure accuracy.
Dosage Reference
Clinical sleep studies: 3 g/day glycine taken 30–60 minutes before bed. No established upper limit. Safe at doses up to 9 g/day in research settings. Non-hormonal, non-habit-forming.
Key Studies Referenced:
- Bannai M, Kawai N, Ono K, et al. (2012). "The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers." Frontiers in Neurology, 3, 61.
- Inagawa K, Hiraoka T, Kohda T, et al. (2006). "Subjective effects of glycine ingestion before bedtime on sleep quality." Sleep and Biological Rhythms, 4(1), 75–77.
- Yamadera W, Inagawa K, Chiba S, et al. (2007). "Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes." Sleep and Biological Rhythms, 5(2), 126–131.
Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement regimen. Individual results may vary.
