Glycine
SupplementThe gap between the medical score (72) and the community score (85) reflects user enthusiasm for sleep effects [c1, c2, c3], which exceeds the clinical evidence base characterized by small study sample sizes [s1, s2]. Additionally, users subjectively report stronger effects than those objectively measured in the RCTs.
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TL;DR
Glycine is a non-essential amino acid that acts as an inhibitory neurotransmitter via glycinergic Cl⁻ channels and serves as an obligatory NMDA receptor co-agonist. Human RCTs support sleep-promoting, anti-inflammatory, and collagen-supporting effects at oral doses of typically 3–5 g. The benefit-risk profile is favorable with minimal side effect potential. Scientific evidence is solid, though medical consensus lags behind community ratings.
Description
Smallest proteinogenic amino acid with sleep-promoting, anti-inflammatory, and collagen-supporting effects; well-supported by multiple human RCTs [s1, s2, s3].
Glycine (aminoacetic acid) is the structurally simplest and smallest proteinogenic amino acid. It is considered conditionally essential: the body synthesizes glycine endogenously, but often in amounts insufficient to fully meet physiological demands [s4]. Glycine is a major constituent of collagen (approximately 33% of amino acids) and thus indispensable for skin, tendons, joints, and bone [s5]. In the central nervous system, glycine acts as an inhibitory neurotransmitter via glycinergic receptors (analogous to GABA-A) and as an obligatory co-agonist at the NMDA receptor [s6]. Through this dual role, glycine influences both sedating and excitatory processes. Multiple RCTs have demonstrated that 3 g of glycine taken before bedtime improves subjective and objective sleep quality, reduces sleep onset latency, and decreases daytime sleepiness [s1, s2]. Glycine is also a precursor of glutathione, the central endogenous antioxidant, and plays a role in lipid metabolism (bile acid conjugation), heme biosynthesis, and immunomodulation [s3, s4]. In obesity and type 2 diabetes, plasma glycine levels are demonstrably reduced, correlating with insulin resistance [s7, s8]. However, clinical supplementation studies show only moderate or inconsistent effects on glucose and insulin levels [s8]. In psychiatric conditions (schizophrenia), high glycine doses (0.4–0.8 g/kg body weight) have been investigated as an adjunct therapy, with mixed results regarding negative symptoms [s9]. Blood-brain barrier permeability is limited, which accounts for the central nervous system effects observed at low doses [s9]. Glycine is clinically safe at daily doses up to 6 g; no relevant toxicity has been reported up to 0.8 g/kg body weight [s10]. The profile is characterized by high tolerability and low cost.
Legal Status (DE)
In Germany, glycine is freely marketable as a food supplement (NEM) under the LFGB and NemV without prescription. A BVL general administrative act pursuant to § 54 LFGB explicitly permits the placing on the market of food supplements containing added glycine. Regulatory approval is not legally required; therapeutic claims are prohibited [s11, s12].
Mechanism of Action
1. Inhibitory neurotransmission: Glycine activates glycinergic Cl⁻ channels in the brainstem and spinal cord, leading to neuronal hyperpolarization and suppression of neuronal excitability. This accounts for the sedating and anxiolytic effects [s6, s1]. 2. NMDA receptor co-agonism: Glycine binds obligatorily to the GluN1 subunit of the NMDA receptor and is required for its full activation. High glycine doses can modulate NMDA activity, which has been investigated for psychiatric applications (schizophrenia, negative symptoms) [s6, s9]. 3. Sleep mechanism: Glycine lowers core body temperature via peripheral vasodilation (NMDA activation in peripheral blood vessels). This cooling promotes the transition into NREM deep sleep. Additionally, glycine influences serotonergic pathways in the suprachiasmatic nucleus [s1, s2]. 4. Collagen biosynthesis: As the most abundant amino acid in collagen (approx. 33%), glycine is structurally indispensable for triple helix formation. In vitro and animal data show that high glycine concentrations increase collagen synthesis in fibroblasts [s5]. 5. Glutathione precursor: Together with glutamate and cysteine, glycine serves as a substrate for glutathione synthesis. Supplementation can increase antioxidant capacity in states of glutathione depletion (e.g., in elderly individuals) [s3, s4]. 6. Anti-inflammatory effects: Glycine modulates macrophage and mast cell activation via a glycine-gated Cl⁻ channel and inhibits pro-inflammatory cytokines (IL-6, TNF-α). This has been demonstrated primarily in animal and in vitro studies [s3]. 7. Metabolic effects: Glycine is involved in bile acid conjugation and heme biosynthesis. Glycine levels are reduced in metabolic syndrome; associations with insulin resistance are documented but not yet conclusively established as causal [s7, s8].
Dosing
Schlafqualität
- Dose
- 3 g
- Frequency
- 1× täglich abends
- Route
- oral
- Duration
- fortlaufend
- Timing
- 30–60 minutes before bedtime
- With food
- optional
Kollagenunterstützung / Gelenkgesundheit
- Dose
- 3–5 g daily (together with vitamin C)
- Frequency
- 1× täglich
- Route
- oral
- Duration
- mindestens 8–12 Wochen
- Timing
- Morning on an empty stomach or with a meal
- With food
- optional
Metabolisches Syndrom (explorativ)
- Dose
- 5–15 g daily
- Frequency
- aufgeteilt auf 2–3 Dosen
- Route
- oral
- Duration
- 12 Wochen
- Timing
- With meals
- With food
- empfohlen
Adjuvante Therapie Schizophrenie (klinisch, hoch dosiert)
- Dose
- 0.4–0.8 g/kg body weight daily (under medical supervision only)
- Frequency
- aufgeteilt auf 2–3 Dosen
- Route
- oral
- Duration
- 6–8 Wochen
- Timing
- Under medical supervision
- With food
- empfohlen
No officially established Tolerable Upper Intake Level (UL) for glycine by EFSA or DGE. Clinical safety documented up to 6 g/day over 4 weeks [s10]. No toxicity signal up to 0.8 g/kg body weight (equivalent to ~56 g/day for a 70 kg individual); however, long-term data at such doses in humans are lacking. Gastrointestinal discomfort may occur at doses above 15 g/day [s10, s13].
Typical sleep dosage in studies: 3 g orally, 30–60 min before bedtime [s1, s2]. Glycine has a mildly sweet taste and dissolves readily in water. For collagen-related effects, concurrent intake of vitamin C is recommended as a cofactor in collagen synthesis [s5].
Side Effects
| Side Effect | Frequency | Severity |
|---|---|---|
| Gastrointestinale Beschwerden (Übelkeit, Magenkrämpfe, weicher Stuhl) Rare at standard sleep doses (3 g); more frequent at high doses above 15 g/day. Generally well tolerated [s10, s13]. | gelegentlich | leicht |
| Tagesmüdigkeit oder verstärkte Schläfrigkeit Due to glycinergic and serotonergic effects on sleep regulation; occurs primarily with evening intake of higher doses [s1, s2]. | gelegentlich | leicht |
| Vorübergehend gestörter Schlaf (paradoxe Wirkung bei einzelnen Nutzern) Individual Reddit users report worsened sleep or no effect; possible inter-individual differences in NMDA sensitivity [c1, c2]. | selten | leicht |
| Erbrechen oder Durchfall bei sehr hohen Dosen (>15 g/Tag) Limited to high supplementation doses; no notable gastrointestinal toxicity at usual dosages [s10, s13]. | selten | leicht |
Contraindications
In impaired renal function, renal excretion of amino acids may be compromised; risk of accumulation at high doses. No specific study for glycine, but general principle applies to amino acid supplementation [s10].
Although extremely rare, glycine should be avoided in cases of known intolerance. Hypersensitivity reactions are theoretically possible [s13].
High doses of glycine may attenuate the efficacy of clozapine in schizophrenia; possible pharmacodynamic interaction at the NMDA receptor [s9].
Interactions
Synergistic
Vitamin C is a cofactor of prolyl and lysyl hydroxylase, which are required for collagen maturation. Combined intake with glycine is beneficial for collagen support [s5].
Glycine and NAC are jointly precursors of glutathione synthesis. Combination can correct glutathione deficiency more effectively than glycine alone [s4].
Glycine as a free amino acid can complement bioavailability in collagen supplementation; combined intake is frequently reported in the biohacking community [s5, c4, c5].
Glycine and magnesium act synergistically on GABAergic and glycinergic receptors and can jointly promote sleep quality and relaxation. Magnesium activates GABA receptors, while glycine additionally lowers core body temperature and supports sleep.
Glycine is a direct precursor of endogenous creatine synthesis (from arginine, glycine, and methionine). Combined supplementation can synergistically support muscle energy supply and muscle building.
Zinc and glycine interact at the zinc-binding site of the NMDA receptor, with both modulating neuronal excitability. This combination is relevant in the context of cognitive support and sleep optimization.
Caution
High glycine doses (>30 g/day) may attenuate the antipsychotic effect of clozapine; do not combine without psychiatric supervision [s9].
Additive sedative effect through enhanced GABAergic and glycinergic inhibition is theoretically possible; clinical relevance at sleep doses (3 g) is low [s1, s6].
Studies
Tier A — High Evidence
Outcome: Subjective daytime sleepiness (VAS) and cognitive performance the following day
Effect Size: Significant reduction in daytime sleepiness; improved concentration and memory performance
Outcome: Improvement of subjective sleep quality (OSA sleep questionnaire) and polysomnography parameters
Effect Size: Significant reduction in sleep onset latency; improved slow-wave sleep proportion; p<0.05 for subjective sleep quality
Outcome: PANSS negative symptoms in schizophrenia
Effect Size: Significant reduction in PANSS negative symptoms vs. placebo with glycine 0.8 g/kg
Tier B — Moderate Evidence
Outcome: Metabolic parameters in severe obesity following glycine supplementation
Effect Size: No significant effect on fasting glucose/insulin; elevation of plasma glycine levels confirmed
Outcome: Sleep and health effects of glycine in adults
Effect Size: Consistent evidence for sleep improvement with 3 g; safety profile confirmed
Outcome: Association between plasma glycine and insulin resistance/obesity
Effect Size: Plasma glycine −11% in obesity, −15% in T2DM vs. healthy controls (pooled meta-analysis)
Tier C — Low Evidence
Outcome: Anti-inflammatory and immunomodulatory effects of glycine
Effect Size: Mechanistic evidence from cell lines and animal models; limited human studies
Outcome: Physiological role of glycine and glutathione precursor
Effect Size: Mechanistic and animal experimental evidence predominate
Outcome: Collagen synthesis in fibroblasts at high glycine concentration
Effect Size: Increased collagen production demonstrated in cell culture at high glycine concentrations
Community Evidence
Top reported benefits
- Faster sleep onset and deeper sleep
- Reduced daytime fatigue the following morning
- Relaxing sensation before bedtime
- Support of collagen and joints (usually in combination with collagen peptides)
- Mildly anxiolytic effect / stress reduction
Top reported issues
- No or barely perceptible sleep effect in some users
- Occasionally paradoxical effect: worsened sleep in individual users
- Mild gastric discomfort when taken on an empty stomach (rare)
Some users report absent effects despite correct dosing (3 g in the evening) [c1, c2]. Isolated reports of increased vivid dreaming or sleep interruptions, presumably due to individual NMDA sensitivity [c1]. Effects on libido and sexual function are discussed in one thread without clear consensus [c3]. Glycine is frequently underestimated and referred to by the community as the "cheapest effective sleep aid" [c2, c4].
Scientific Sources
- 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
Kumar P, Liu C, Hsu JW, Chacko S, Minard C, Jahoor F, Bhatt R (2023). The Journals of Gerontology: Series ABPMID:35975308DOI - Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes
Yamadera W, Inagawa K, Chiba S, et al. (2007). Sleep and Biological RhythmsADOI - Glycine: Overview, Uses, Side Effects, Precautions, Interactions, Dosing and Reviews
WebMD Editorial Team (2024). WebMD/Natural MedicinesBLink - BVL Allgemeinverfügung gemäß § 54 LFGB – Nahrungsergänzungsmittel mit Glycin
Bundesamt für Verbraucherschutz und Lebensmittelsicherheit (BVL) (2017). BVL Bundesrepublik DeutschlandALink - Rechtliche Grundlagen von Nahrungsergänzungsmitteln (LFGB/NemV)
aakamp Rechtsanwälte (2023). aakamp.deBLink - Tolerable Upper Intake Level for Individual Amino Acids in Humans: A Narrative Review of Recent Clinical Studies
Wu G, Fanzo J, Miller DD, et al. (2023). Journal of NutritionALink - The Effects of Glycine on Subjective Daytime Performance in Partially Sleep-Restricted Healthy Volunteers
Bannai M, Kawai N, Ono K, et al. (2012). Frontiers in NeurologyAPMID:22529837DOI - Glycine: The Smallest Anti-Inflammatory Micronutrient
Razak MA, Begum PS, Viswanath B, et al. (2017). Advances in NutritionBLink - An Update of the Promise of Glycine Supplementation for Enhancing Physical Performance and Recovery
Tinsley GM, Moore ML, Graybeal AJ, et al. (2024). NutrientsBLink - High glycine concentration increases collagen synthesis by articular chondrocytes in vitro
Albaugh VL, Mukherjee K, Barbul A, et al. (2017). Clinical Nutrition ESPENCLink - The glycine site of NMDA receptors: A target for cognitive enhancement in psychiatric disorders
Forsyth JK, Bhatt DL, Bhatt SB, et al. (2017). Neuroscience & Biobehavioral ReviewsBDOI - Glycine Metabolism and Its Alterations in Obesity and Metabolic Diseases
Alves A, Bassot A, Bulteau AL, et al. (2019). NutrientsBPMID:31200513DOI - Metabolic impact of dietary glycine supplementation in individuals with severe obesity
Gonzalez-Ortiz A, Cariou B, Sanna M, et al. (2025). Scientific ReportsBDOI - Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia
Heresco-Levy U, Javitt DC, Ermilov M, et al. (1999). Archives of General PsychiatryAPMID:9892253
Community Sources
Storage
Unopened
Store dry, at room temperature (15–25 °C), protected from light and moisture.
Opened
Keep container tightly sealed; when in powder form, carefully avoid moisture exposure, as glycine is hygroscopic.
Notes
Glycine powder is stable and not temperature-sensitive. Refrigeration is not required. Typical shelf life is 2–3 years.