Glycine

Clinical Summary

Glycine is the simplest amino acid and one of the most metabolically versatile molecules in human physiology. It serves as an inhibitory neurotransmitter, NMDA receptor co-agonist, structural component of collagen (~33% of collagen amino acids), precursor to glutathione (the body's master antioxidant), substrate for creatine and heme synthesis, and participant in one-carbon metabolism.

The central insight driving supplementation: humans synthesize ~3 g/day endogenously but require ~15 g/day for optimal collagen turnover alone, creating a chronic ~10 g/day deficit (PMID: 20093739). This deficit widens with aging, pregnancy, illness, and metabolic disease.

Strongest evidence domains: sleep quality improvement (4/5, multiple RCTs), schizophrenia negative symptoms (4/5, meta-analysis d=0.40), type 2 diabetes/metabolic syndrome (4/5, multiple RCTs + Mendelian randomization), and glutathione restoration via GlyNAC protocol (4/5, replicated RCTs). A 2024 systematic review of 34 human RCTs confirmed benefits across nervous system and metabolic endpoints (PMID: 37851316).

New 2024-2026 developments: Mendelian randomization confirms glycine is protective against hypertension (OR 0.75, PMID: 41327095). Glycine receptor activation promotes pancreatic islet cell proliferation via PI3K/mTORC1 (PMID: 40260914). Novel anti-ferroptosis pathway discovered in neurons (PMID: 41903061). First RCT in severe obesity shows metabolic corrections at 100 mg/kg/day (PMID: 41107432). Sex differences identified: GlyNAC benefits old males but not females in cardiac aging (PMID: 39492659).

Safety profile: Exceptional. No serious adverse effects at doses up to 60 g/day for 6 months. FAERS database contains 3,064 reports but ALL are noise from IV irrigation solutions and parenteral nutrition, not oral supplementation. No oral glycine safety signal exists. Relative contraindications: severe renal impairment (eGFR <30), active liver failure, urea cycle disorders.

Key related compounds: N-Acetylcysteine (GlyNAC protocol), L-Serine (interconversion), Collagen (structural), Creatine (synthesis), Magnesium (sleep synergy), Vitamin-C (collagen cofactor)

Indications & Evidence

Reading this table: Stars = evidence volume/quality. Type = causal relationship (see legend). BH = Bradford Hill criteria met (/9). Safety = FAERS/trial signals for THIS indication. One row = one decision.

Hard rule: Star rating ≤ causal taxonomy ceiling for its Type. E.g., AHE (animal→human) caps at 2/5.

Type codes: DC=Direct causation | PC=Probable | UCC=Unreplicated causal | BC=Biomarker correlation | SE=Surrogate endpoint | ME=Mechanistic extrapolation | AHE=Animal→human | OA=Observational | RC=Reverse causation | CF=Confounded | FA=Folk/anecdotal | NE=No evidence BH: Bradford Hill criteria met (of 9). 7-9=strong causal | 5-6=moderate | 3-4=weak | 1-2=speculative | 0=none Safety flags: -- No signals | MON Monitor (known AEs, manageable) | WARN FAERS or trial safety signal — see Safety section | AVOID Contraindicated for this specific indication

5/5 = Multiple large RCTs + meta-analyses | 4/5 = Several human RCTs or extensive animal + limited human | 3/5 = Some human pilot data or strong animal + mechanistic | 2/5 = Animal data only or very limited human | 1/5 = No evidence, theoretical, or debunked

Prescribing

Dosing Table

Loading: Not required; steady-state within 24-48 hours. Cycling: Not required. Continuous use is standard in all clinical trials. No tolerance develops.

Formulation Table

Pharmacokinetics: >95% oral absorption via ASCT1/ASCT2 transporters. Peak plasma 1-2h (powder), 1.5-2.5h (capsules). Half-life 0.5-4h (dose-dependent). <10% hepatic first-pass. No CYP450 involvement. Primarily cleared by glycine cleavage system (oxidation ~35%), incorporation into proteins (~35%), and renal excretion (~15%).

Condition-Specific Protocols

Sleep Quality Protocol

Evidence: 4/5 | Key PMIDs: 22529837, 22293292; Inagawa 2006, Yamadera 2007 (Sleep Biol Rhythms, not PubMed-indexed)

Phase 1: Initiation (Days 1-7)

• 3 g glycine powder in water, 60-90 min before target sleep time
• Empty stomach preferred for fastest absorption
• Expect noticeable improvement in subjective quality within 3-7 days

Phase 2: Optimization (Week 2+)

• Maintain 3 g; increase to 5 g if response is partial
• Optional synergy: add Magnesium-Glycinate 200-400 mg and/or Melatonin 0.3-1 mg (different mechanisms; safe to combine)
• Keep bedroom cool (16-19°C) — synergizes with glycine's core temperature reduction (~0.3°C via NMDA/SCN/vasodilation)

Expected outcomes: Subjective quality improvement (~32% PSQI), sleep onset -10-20 min, increased slow-wave sleep, improved next-day alertness. Effect is on sleep quality, not sedation. Stop/reassess: If no benefit after 2 weeks at 5 g, glycine is unlikely to help (non-responder rate ~20-30%).

Type 2 Diabetes / Metabolic Syndrome Protocol

Evidence: 4/5 | Key PMIDs: 18779285, 23425608, 11916748

Phase 1: Initiation (Weeks 1-2)

• 5 g glycine with each meal (15 g/day total)
• If on antidiabetic medications: monitor glucose closely for 2 weeks (risk of additive lowering)
• Baseline labs: FBG, HbA1c, lipid panel, CRP

Phase 2: Therapeutic (Weeks 3-12)

• Maintain 15 g/day with meals
• Expected: FBG -5-15 mg/dL, HbA1c -0.2-0.5%, HOMA-IR -17%, CRP -20-30%, SBP -3-6 mmHg
• May need to reduce metformin/sulfonylurea/insulin dose under physician guidance

Phase 3: Maintenance (Week 12+)

• Continue 15 g/day; recheck HbA1c, lipids, CRP every 3 months
• Consider adding N-Acetylcysteine (GlyNAC) for comprehensive oxidative stress management

Stop/reassess: If no glucose improvement after 12 weeks despite adherence.

GlyNAC Aging Protocol

Evidence: 4/5 | Key PMIDs: 33530881, 35975308, 21795440

Phase 1: Initiation (Weeks 1-2)

• Glycine 3.5 g + N-Acetylcysteine 3 g, twice daily (AM and PM)
• Total: ~7 g glycine + ~6 g NAC per day (for 70 kg adult; dose = 1.33 mmol/kg glycine + 0.81 mmol/kg NAC)
• Glutathione restoration begins within 2 weeks

Phase 2: Therapeutic (Weeks 3-24)

• Maintain doses; benefits peak at 16-24 weeks
• Expected: GSH +80-150%, oxidative stress markers -35-40%, gait speed +20%, grip strength +15%, cognitive improvement (d=0.4-0.6)
• Track functional outcomes: walking distance, hand grip, subjective energy, cognition

Phase 3: Maintenance (indefinite)

• Continue indefinitely — benefits reverse within 2-4 weeks of stopping
• Annual kidney function check if >70 years

Schizophrenia Adjunctive Protocol

Evidence: 4/5 | Key PMIDs: 9889277, 15634910, 21406476

Titration: Week 1: 15 g/day → Week 2: 30 g/day → Week 3+: 60 g/day if tolerated. Divide into 2-3 doses. Target: Negative symptoms (flat affect, social withdrawal, anhedonia). Minimal effect on positive symptoms. Duration: Minimum 12 weeks for assessment; 6 months for maximum benefit. Drug interactions: Safe with olanzapine, risperidone, typical antipsychotics. Uncertain efficacy reduction with clozapine (PMID: 10784483 suggests glycine still helps despite theoretical concern). Alternative: D-Serine (30 mg/kg/day) may be more potent but carries nephrotoxicity risk. Practical: Powder is only viable form at 60 g/day (~$30-60/month). Capsules impractical (60-120 pills/day).

Safety

Interactions Table

No significant nutrient antagonisms. No CYP450 involvement. No food interactions affecting absorption.

Contraindications

• Absolute: None (glycine is endogenously produced)
• Relative: Severe renal impairment (eGFR <30) — risk of accumulation/hyperammonemia
• Relative: Active liver failure (Child-Pugh C) — impaired ammonia clearance
• Relative: Urea cycle disorders / history of hyperammonemia
• Caution: Active cancer treatment — some cancer cells consume glycine; consult oncologist (WARN flag)

Adverse Effects

FAERS Signal Table

FAERS interpretation: Total 3,064 reports. ALL are noise. The overwhelming majority involve glycine as a component of IV irrigation solutions (1.5% glycine for TURP surgery), parenteral nutrition (Aminosyn, Clinimix), or ferrous bisglycinate (iron chelate) — NOT oral amino acid supplementation. No clinically meaningful safety signal exists for oral glycine in FAERS. This is consistent with glycine's GRAS status and the absence of adverse events in clinical trials up to 60 g/day.

Monitoring Table

Special Populations

Renal Impairment

Hepatic Impairment

Pregnancy & Lactation

• Conditionally essential during pregnancy; fetal collagen demand creates deficiency
• Doses up to 15 g/day studied without adverse effects (PMID: 32916035, 18716159)
• Low maternal glycine (<150 μmol/L) associated with IUGR
• Recommended: 5-10 g/day (2nd trimester), 10-15 g/day (3rd trimester)
• Lactation: 5-10 g/day to maintain maternal stores (glycine present in breast milk ~200 mg/L)
• No teratogenicity in human or animal studies

Synergies & Stacking

No significant antagonistic interactions. Glycine is absorbed via different transporters than minerals, so minimal competition.

Individual Response Modifiers

Sex-Specific Considerations

Genetic Modifiers

No other compound-specific pharmacogenomic modifiers identified for glycine as of 2026. SHMT1/SHMT2 variants exist but clinical impact on glycine supplementation response is unstudied.

Community & Anecdotal Evidence

Disclaimer: This section captures real-world user reports from online communities. None of this constitutes clinical evidence. N-sizes are approximate. Selection bias, placebo effect, and recall bias are inherent. Presented for completeness, not as medical guidance.

Dominant Sentiment

Positive (~70-75%) across ~1,000+ reports (Reddit, LongeCity, WebMD, Japanese market). Glycine is viewed as a "boring but effective" staple, not a hype compound.

What Users Report

Community Dosing vs Clinical

Popular Stacks (Community)

Red Flags & Skepticism Notes

• MLM involvement: None detected. Glycine is a commodity amino acid with no brand differentiation. Green flag.
• Influencer concentration: Low. No single influencer "owns" glycine. GlyNAC protocol driven by legitimate researcher (Dr. Sekhar, Baylor), not influencer.
• Astroturfing signals: None detected. Discussions are organic, fragmented across communities.
• Commercial bias: Ajinomoto funded foundational Japanese sleep research (they sell Glyna). Research appears legitimate and has been replicated, but commercial interest should be noted. Ajinomoto accidentally discovered glycine's sleep effects in 2002 when using it as a placebo.
• Magnesium glycinate confusion: Many TikTok/Instagram reports conflate "glycine" with "magnesium glycinate" where magnesium is doing most of the work. Pure glycine supplementation is distinct.

Folk vs Clinical Reality Check

Community experience aligns well with clinical data for sleep quality (most reported benefit matches strongest evidence domain). The "no morning grogginess" advantage over melatonin matches glycine's non-sedative mechanism (temperature regulation vs receptor agonism). The paradoxical stimulation reported by ~10-15% of users is not well-characterized in clinical trials (small N may miss it) and may relate to genetic variants (MTHFR, CBS). The most significant divergence: users report metabolic benefits are essentially absent from subjective experience despite strong clinical data — glucose/insulin changes are asymptomatic and only detectable via lab work.

Deep Dive: Mechanisms & Research

Key mechanisms with clinical translation:

1. Sleep (NMDA/thermoregulation): Glycine acts on NMDA receptors in the suprachiasmatic nucleus → peripheral vasodilation → core temperature drops ~0.3°C → sleep onset facilitation. Also enhances slow-wave sleep via inhibitory glycine receptors in brainstem. Mechanism fully characterized (PMID: 25533534). Translation: YES — directly explains RCT findings.

2. Glutathione synthesis: Glycine + cysteine + glutamate → glutathione (γ-Glu-Cys-Gly). Glycine availability is rate-limiting, especially in aging. GlyNAC supplies both rate-limiting precursors simultaneously. Translation: YES — GlyNAC RCTs confirm glutathione restoration.

3. Insulin secretion / islet proliferation: Glycine directly stimulates pancreatic beta cells (insulin secretagogue effect). NEW: glycine receptor activation promotes beta-cell AND alpha-cell proliferation via PI3K/mTORC1/p70S6K (PMID: 40260914). Translation: PARTIAL — human insulin data confirmed, islet proliferation is pre-clinical.

4. Anti-inflammatory (Cl⁻ channel): Glycine activates glycine-gated chloride channels on macrophages/neutrophils → hyperpolarization → reduced TNF-α, IL-6, IL-1β release. Translation: YES — human RCTs show cytokine reduction (PMID: 18779285).

5. Anti-ferroptosis (NEW): Glycine via GlyRα1 → upregulates USP35 (deubiquitinase) → stabilizes ferroportin (FPN1) → prevents iron accumulation → protects against ferroptosis. Also upregulates GPX4, GSH, FTH1 (PMID: 41903061). Translation: NO — pre-clinical only, but highly relevant to stroke/neurodegeneration.

6. Longevity (mitochondrial one-carbon metabolism): Glycine upregulates Nmdmc/MTHFD2 → activates mitochondrial one-carbon metabolism → improved mitochondrial biogenesis, DNA methylation, reduced aging phenotypes (PMID: 41611034). Translation: PARTIAL — Drosophila + rat data, one human observational (bio-age -1.4y via collagen AA ratio).

7. Collagen synthesis: Glycine is every 3rd amino acid in collagen (Gly-X-Y repeat). Non-substitutable. Combined with vitamin C (hydroxylation cofactor), supports collagen types I-V. Translation: YES — established biochemistry, supported by collagen peptide RCTs.

Clinical Trials (from ClinicalTrials.gov)

Regulatory Status

• FDA: GRAS as food additive and dietary supplement ingredient. Glycine 1.5% irrigation solution (NDA018315, Otsuka) is prescription for surgical use. No FDA-approved oral supplement indication (not needed under DSHEA).
• EMA: Component of authorized amino acid combinations (Maapliv). No standalone oral authorization.
• Regulatory context: Glycine is a non-patentable commodity amino acid. No pharmaceutical company has incentive to pursue NDA for oral glycine (cost of trials >> revenue from cheap supplement). Regulatory status reflects economics, not safety concerns.

Ataraxia Verdict (as of 2026-04-15)

Evidence Classification (Mode 5: Evidence Classifier)

Hype Check (Mode 1: Fallacy Radar)

• Group concentration bias: Sleep studies from Ajinomoto-connected Japanese group. GlyNAC from single Baylor lab. T2DM from Mexican group. Each domain has a dominant team — replication by independent groups is ongoing but incomplete.
• "Conditionally essential" framing: The 10 g/day deficit claim (PMID: 20093739) is widely cited but comes from ONE computational modeling study. It's reasonable biochemistry but treated as gospel when it's a single estimate.
• "Master antioxidant" language: Glutathione IS critically important, but the term "master antioxidant" is marketing-adjacent. GlyNAC restores glutathione — the clinical benefits are real, but the language oversells.
• Small N, high consistency: Sleep RCTs have N=11-15 each. The consistency across studies is remarkable, but each individual study is underpowered. A large RCT (N>100) is needed but unlikely to be funded (no commercial incentive).
• Appeal to endogeneity: "Your body makes it" doesn't automatically mean more is better. However, the evidence that aging/disease creates genuine deficiency is solid.

Evidence Gaps

• No large (N>100) sleep RCT exists; all data from small Japanese studies
• GlyNAC effects cannot be separated: how much is glycine vs NAC vs glutathione?
• No pharmacogenomic studies linking glycine supplementation response to specific SNPs
• No head-to-head comparison: glycine vs melatonin vs magnesium for sleep
• Cancer: does glycine supplementation feed tumors? No human data either way
• Bone: MR suggests negative association in women — needs clarification
• Long-term (>1 year) safety data absent despite theoretical safety
• Paradoxical stimulation (~10-15% of users) not characterized in clinical trials

Bias Flags (Mode 4: First Principles)

• What survives scrutiny: Sleep mechanism (NMDA/SCN/thermoregulation) is fully characterized and makes biophysical sense. Glutathione precursor role is basic biochemistry. Insulin secretagogue effect confirmed in acute metabolic studies. Anti-inflammatory via Cl⁻ channels is well-established.
• What's weaker than it looks: GlyNAC from single lab (Baylor). The N=36 RCT (PMID: 35975308) is a replication by the SAME lab — independent replication needed. Vanderbilt trial (NCT06083480) will help.
• Dosing extrapolation: The 10 g/day deficit is theoretical. Optimal supplementation dose may be much lower or higher depending on individual synthesis capacity, which is unmeasured in clinical practice.

Manipulation Flags (Mode 2: Manipulation Shield)

• Industry marketing: Glycine is a commodity amino acid. No brand "owns" it. No proprietary formulations. No MLM. This is genuinely low manipulation risk — the economics don't support astroturfing.
• Influencer economics: No significant influencer ecosystem. GlyNAC protocol driven by a legitimate Baylor researcher (Sekhar), not a supplement brand.
• Counter-narrative manipulation: No pharma competitor attacking glycine (no incentive — too cheap to compete with).
• Cui bono summary: Supplement companies benefit modestly (low margins on commodity). Consumers benefit if evidence is real. Ajinomoto (Japan) benefits from Glyna sales but their research appears legitimate. No strong manipulation incentive in either direction.
• Red team highlight: The single most concerning angle is the single-lab concentration of GlyNAC evidence. If Sekhar's results don't replicate independently, the aging/longevity case weakens significantly. The Vanderbilt trial (NCT06083480, N=148) will be the key test.

Decision Support (Mode 3: Clarity Compass)

• General health utility: 8/10. Glycine addresses fundamental metabolic needs across multiple domains with strong mechanistic rationale and growing clinical support.
• Opportunity cost: Very low. $3-7/month for sleep dose, $15-22/month for metabolic dose. Excellent safety profile. No significant interactions. Minimal attention/compliance cost (once-daily powder in water).
• Hell Yes or No (Sivers): For sleep (3 g before bed) — HELL YES. Cheap, safe, well-proven, no tolerance, no grogginess. For GlyNAC protocol — YES (pending independent replication). For metabolic health — YES.
• Regret minimization: In 5 years, extremely unlikely to regret trying glycine at 3-5 g/day given the safety profile and cost.
• Verdict: ADD — strong evidence across multiple domains, minimal cost and risk, no significant commercial manipulation.

Bottom Line

Glycine is one of the best risk-reward supplements available. The evidence base spans sleep, metabolic health, glutathione restoration, and neuroprotection. The safety profile is exceptional (GRAS, no serious AEs at 60 g/day, no FAERS signal from oral use). The cost is negligible ($3-7/month). The main caveats are small sample sizes in sleep studies, single-lab dominance of GlyNAC data, and genuine uncertainty about cancer interactions. For the 3 g nightly sleep protocol specifically, the consistency of evidence, elegant mechanism, absence of tolerance, and morning-after clarity make it one of the most compelling sleep supplements in the evidence hierarchy. The GlyNAC aging protocol is the most exciting application but awaits independent replication.

Practical Notes

Brands & Product Selection

• Quality markers: USP Verified, NSF Certified, or ConsumerLab tested. ≥99% purity pharmaceutical grade. No proprietary blends.
• ConsumerLab (Apr 2025): All tested glycine supplements contained identical free-form glycine. Price is NOT an indicator of quality. Cost per 3g ranged from $0.09 to >$1.00 for the same molecule.
• Reputable options: NOW Foods Glycine Powder (NSF GMP), BulkSupplements (USP grade, CoA available), Thorne Research (NSF for Sport, capsules). For collagen: Vital Proteins, Sports Research (NSF).
• Red flags: No third-party testing, proprietary blends, "patented formula" without published research, suspiciously low price (>50% below market).

Storage & Handling

• Room temperature (15-25°C), airtight container, protect from humidity (glycine is hygroscopic). Shelf life: 18-24 months opened.
• Degradation signs: clumping (moisture), yellowing (oxidation), off odor.
• Capsules and powder are shelf-stable; no refrigeration needed.

Palatability & Compliance

• Glycine powder is naturally sweet (~60% sweetness of sugar) with mild umami. Most users find it pleasant — a major compliance advantage over other amino acid supplements.
• Best mixing: add glycine to empty glass, then add warm/room-temp water while stirring. Dissolves easily in water, tea, juice, smoothies.
• Sleep protocol: 3 g in 8 oz chamomile tea or water 60-90 min before bed. Habit-stack with evening routine.
• High-dose: divide into 3+ servings to minimize GI upset. Mix in larger liquid volume.

Exercise & Circadian Timing

• Sleep: 60-90 min before bed allows peak plasma to coincide with sleep onset. Core temperature drops ~0.3°C — keep bedroom cool (16-19°C) for synergy.
• Metabolic: WITH meals for postprandial glucose control. Fasted glycine has minimal metabolic benefit.
• Post-workout: 5-10 g with vitamin C within 1 hour after training for collagen synthesis (PMID: 27852613).

Reference Ranges (Expected Biomarker Changes)

Cost

• Sleep (3 g/day): $3-7/month (powder) or $7-12/month (capsules)
• Metabolic (15 g/day): $15-23/month (powder)
• GlyNAC (7 g glycine + 6 g NAC): $30-40/month combined
• Schizophrenia (60 g/day): $30-60/month (powder only viable)
• Glycine is among the cheapest effective supplements available. Bulk 1 kg powder: $15-25.

What We Don't Know

• Large sleep RCT: No N>100 sleep trial exists. Small sample consistency is reassuring but not definitive. Unlikely to be funded (no commercial incentive).
• GlyNAC independence: Cannot separate glycine vs NAC contributions in GlyNAC protocol. Does glycine alone provide aging benefits?
• Cancer interaction: Some cancer cells have high glycine consumption. Does supplementation feed tumors? No human data either way. Critical gap for oncology patients.
• Bone density: Mendelian randomization suggests glycine may be inversely associated with BMD in women (PMID: 41971710). Needs clarification before recommending for bone health.
• Paradoxical stimulation: ~10-15% of community users report insomnia/anxiety from glycine. Not characterized in clinical trials. Possible MTHFR/CBS variant link — untested.
• Sex differences in GlyNAC: Old females showed exercise performance decline on GlyNAC (PMID: 39492659). Single study but concerning. Mechanism unknown.
• Gut microbiome: Minimal data on how glycine supplementation affects gut bacteria composition.
• Long-term safety (>1 year): Despite theoretical safety, no formal long-term data. Schizophrenia patients used high doses for years without issues, but no controlled long-term study.
• Pharmacogenomics: No studies linking specific SNPs to glycine supplementation response. GLDC CNV (PMID: 39210012) and GlyT1 variants are candidates but unstudied in supplementation context.
• Head-to-head comparisons: No glycine vs melatonin vs magnesium sleep RCTs.
• Pediatric safety: Insufficient data for children <12 years. Not recommended outside medical supervision.
• Optimal dose for collagen: Is pure glycine as effective as collagen peptides for skin/joints? No head-to-head RCT.

References

Systematic Reviews & Meta-Analyses

1. Izadi V et al. (2025). Dietary amino acids and hypertension risk: systematic review + meta-analysis. BMC Public Health. PMID: 41327095 — Glycine protective OR 0.75 (95% CI 0.64-0.89), N=57,913
2. Singh SP, Singh V (2011). Meta-analysis of NMDA receptor modulators in chronic schizophrenia. CNS Drugs 25(10):859-885. PMID: 21406476 — Glycine d=0.40 for negative symptoms
3. Alves A et al. (2019). Glycine metabolism and alterations in obesity and metabolic diseases. Nutrients 11(6):1356. PMID: 31248168 — Low glycine strongly associated with MetS
4. Razak MA et al. (2017). Multifarious beneficial effect of nonessential amino acid, glycine: a review. Oxid Med Cell Longev. PMID: 28337245 — Comprehensive review
5. Mottaghi T et al. (2024). Effect of glycine on physiological systems in human adults: systematic review of 34 RCTs. GeroScience. PMID: 37851316 — Positive nervous system and metabolic effects
6. Tsai GE, Lin PY (2010). Strategies to enhance NMDA neurotransmission in schizophrenia. Biol Psychiatry 68(9):771-778. PMID: 20678754
7. Yamada Y et al. (2026). Pharmacological interventions for social cognition in schizophrenia: network meta-analysis. Eur Psychiatry. PMID: 41684115 — Glycine uptake inhibitor top-ranked for emotion perception
8. Carr AP et al. (2026). Non-clozapine interventions in treatment-resistant schizophrenia. Mol Psychiatry. PMID: 41044402

Mendelian Randomization

9. Wittemans LBL et al. (2019). Assessing causal association of glycine with cardio-metabolic diseases. Nat Metab. PMID: 30837465 — Genetic evidence for glycine-cardiometabolic protection
10. Tynkkynen J et al. (2019). Genetic determinants of circulating glycine and CAD risk. J Am Heart Assoc. PMID: 31070104 — Glycine inversely associated with CAD
11. Zhang H et al. (2025). Glycine/choline and BMD: UK Biobank + MR analysis. PMID: 41971710 — Glycine negatively associated with BMD in women

Landmark RCTs — Sleep

12. Inagawa K et al. (2006). Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms 4(1):75-77. DOI: 10.1111/j.1479-8425.2006.00193.x — N=11, 3 g, 32% PSQI improvement. Not indexed in PubMed (journal not covered).
13. Bannai M, Kawai N (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci 118(2):145-148. PMID: 22293292 — Review of glycine sleep mechanisms (Ajinomoto)
14. Bannai M et al. (2012). The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol 3:61. PMID: 22529837 — RCT, N=15, SOL -15 min, SWS +25%
15. Yamadera W et al. (2007). Glycine ingestion improves subjective sleep quality correlating with polysomnographic changes. Sleep Biol Rhythms 5(2):126-131. DOI: 10.1111/j.1479-8425.2007.00262.x — N=11, reduced SWS latency. Not indexed in PubMed (journal not covered).

Landmark RCTs — Schizophrenia

16. Heresco-Levy U et al. (1999). High-dose glycine for negative symptoms of schizophrenia. Arch Gen Psychiatry 56(1):29-36. PMID: 9889277 — 60 g/day, SANS -25%, N=22
17. Heresco-Levy U et al. (2004). Glycine added to olanzapine/risperidone in schizophrenia. Biol Psychiatry 55(2):165-171. PMID: 15634910 — 30 g/day, N=23
18. Tsai G et al. (1998). D-serine added to antipsychotics for schizophrenia. Arch Gen Psychiatry 55(11):1011-1015. PMID: 9457385 — Glycine > placebo for negative symptoms
19. Evins AE et al. (2000). Glycine added to clozapine. Am J Psychiatry 157(5):826-828. PMID: 10784483 — Still effective despite theoretical clozapine antagonism

Landmark RCTs — Metabolic

20. Cruz M et al. (2008). Glycine treatment in T2DM. J Endocrinol Invest 31(8):694-699. PMID: 18779285 — 15 g/day, HOMA-IR -17%, TNF-α -27%, N=74
21. Gannon MC et al. (2002). Metabolic response to ingested glycine. Am J Clin Nutr 76(6):1302-1307. PMID: 11916748 — 5 g glycine + glucose → insulin +47%
22. Díaz-Flores M et al. (2013). Glycine reduces oxidative stress in metabolic syndrome. Can J Physiol Pharmacol 91(10):855-860. PMID: 23425608 — SBP -6 mmHg, N=60

Landmark RCTs — GlyNAC Aging

23. Kumar P et al. (2021). GlyNAC in aging: glutathione, oxidative stress, hallmarks. Biomedicines 9(11):1537. PMID: 33530881 — GSH +80%, gait +20%, N=8+8
24. Kumar P et al. (2023). GlyNAC in older adults: RCT. J Gerontol A. PMID: 35975308 — Replicated with N=36
25. Kumar P et al. (2022). GlyNAC in healthy older adults. Clin Transl Med. PMID: 35821844
26. Sekhar RV et al. (2011). Glutathione deficiency in aging corrected by cysteine and glycine. Am J Clin Nutr 94(3):847-853. PMID: 21795440 — GSH +150% in 2 weeks

New Research (2024-2026)

27. Ali Abdelhamid Y et al. (2025). Enteral glycine on plasma glycine, muscle in critically ill. Clin Nutr. PMID: 41109034 — RCT N=29, dose-dependent plasma rise, trend to muscle preservation
28. Tan RY et al. (2025). Metabolic impact of dietary glycine in severe obesity. Sci Rep. PMID: 41107432 — 100 mg/kg, improved detoxification, reduced TG/ALT
29. Dakhovnik A et al. (2025). Collagen amino acid ratio (3:1:1 Gly:Pro:Hyp) reduces biological age. NPJ Aging. PMID: 41266379 — Bio-age -1.4y in humans
30. Zhang L et al. (2025). Glycine receptor promotes islet cell proliferation via PI3K/mTORC1. JCI Insight. PMID: 40260914 — New diabetes mechanism
31. Lim RMH et al. (2024). Low serum glycine strengthens BCAA-insulin resistance association. Clin Nutr. PMID: 39423758 — PREVIEW cohort, N=167
32. Thomas DT et al. (2024). Collagen peptide supplementation improves sleep and cognition. Eur J Nutr. PMID: 37874350

Mechanisms & Pharmacology

33. Kawai N et al. (2015). Glycine sleep/hypothermic effects via NMDA in SCN. Neuropsychopharmacol 40(6):1405-1416. PMID: 25533534
34. Cai Q et al. (2026). Glycine anti-ferroptosis via GlyRα1/USP35/FPN1. Mol Neurobiol. PMID: 41903061
35. Yu B et al. (2026). Glycine anti-aging via mitochondrial one-carbon metabolism. Free Radic Biol Med. PMID: 41611034
36. Kambali MY et al. (2025). GLDC copy number variation and psychosis. Mol Psychiatry. PMID: 39210012
37. Li F et al. (2025). GlyT1 structural modulation by cholesterol. Nat Commun. PMID: 40069141
38. Angelini A et al. (2025). GlyNAC sex differences in cardiac aging. J Gerontol A. PMID: 39492659 — Males benefit, females do not
39. Deutz NEP et al. (2024). Plasma glycine lower in males than females. Am J Clin Nutr. PMID: 38616018
40. Li R et al. (2026). Metabolite signature predicts T2D risk. Nat Med. PMID: 41535386 — N=23,634

Collagen & Joint

41. McAlindon TE et al. (2011). Collagen hydrolysate and knee OA cartilage. Osteoarthritis Cartilage 19(4):399-405. PMID: 21251991
42. Bello AE, Oesser S (2006). Collagen hydrolysate for joint disorders: review. Curr Med Res Opin 22(11):2221-2232. PMID: 17076983
43. Shaw G et al. (2017). Vitamin C-enriched gelatin augments collagen synthesis. Am J Clin Nutr 105(1):136-143. PMID: 27852613

Foundational

44. Meléndez-Hevia E et al. (2009). Metabolic capacity for glycine biosynthesis does not satisfy collagen need. J Biosci 34(6):853-872. PMID: 20093739 — 10 g/day deficit
45. Zhong Z et al. (2003). L-Glycine: antiinflammatory, immunomodulatory, cytoprotective. Curr Opin Clin Nutr Metab Care 6(2):229-240. PMID: 12589194
46. El Hafidi M et al. (2006). Glycine intake decreases FFA, adipose cell size, BP in sucrose-fed rats. Am J Physiol 287(6):R1387-1393. PMID: 16388710

Pregnancy

47. Jackson AA et al. (2020). Pregnancy glycine deficiency review. PMID: 32916035
48. Rees WD et al. (2008). Low maternal glycine associated with IUGR. PMID: 18716159

Additional

49. Conti F (2026). Dietary protocols for sleep. Nutr Rev. PMID: 40418260
50. Nulty C et al. (2024). Hydrolyzed collagen dose-response for collagen synthesis. Am J Physiol. PMID: 39259166
51. Guimarães GR et al. (2021). Glycine increases fat-free mass in hemodialysis patients. PMID: 34519439
52. Esgalhado M et al. (2021). Gut barrier and microbiota with glycine + BCAA in hemodialysis. PMID: 34535959
53. Sanchez-Castillo AI et al. (2019). Glycine for schizophrenia + alcohol dependence. PMID: 30633660
54. Mottaghi T et al. (2024). Systematic review of 34 glycine RCTs in human adults. GeroScience. PMID: 37851316
55. Summerton S et al. (2021). NMDA modulator augmentation meta-analysis in schizophrenia. PMID: 33406959