What does the research show about glycine?

Glycine

Three small trials of 3 g glycine at bedtime each reported better self-rated sleep or less next-day fatigue. In schizophrenia, a meta-analysis found glycine added to non-clozapine antipsychotics improved total symptoms, while the largest single trial found no effect on negative symptoms. Added to clozapine, glycine worsened positive symptoms.

Add to Bio HackChecked 2026-11-09

Status: Dietary supplement in the US.
Also called: aminoacetic acid, glycine powder, GlyNAC, glycine and N-acetylcysteine
Taken for: sleep quality, falling asleep, daytime fatigue, aging, glutathione, schizophrenia symptoms

Strong several reviews agree · Moderate one review or consistent trials · Limited one or a few small studies · Untested no study in people, listed with what it rests on

Shown to help1

LimitedSmall trials found 3 g of glycine before bed improved self-rated sleep and next-day fatigue in people with poor or shortened sleep.

Reported risks1

LimitedLimited evidence: added to clozapine, glycine worsened positive symptoms in a small subgroup of trials.How often is not known

What people take it for, and what was found

Shown to help1

Limited

Sleep quality and next-day fatigue

Small trials found 3 g of glycine before bed improved self-rated sleep and next-day fatigue in people with poor or shortened sleep.

The numbers and sources

Effect: In people with ongoing unsatisfactory sleep, 3 g of glycine before bed improved self-rated sleep quality and sleep efficiency and shortened polysomnographic latency to sleep onset and to slow-wave sleep, without changing sleep architecture. Daytime sleepiness fell and memory recognition improved [1]. In healthy men whose sleep was cut by 25% for three nights, 3 g at bedtime reduced fatigue on a visual analog scale, showed a trend toward less sleepiness, and improved psychomotor vigilance [2]. A 2026 scoping review found 3 glycine sleep trials, all reporting a benefit on at least one sleep outcome [3].
Population: Volunteers with ongoing unsatisfactory sleep [1]. 10 healthy men aged 30 to 61, all employees of Ajinomoto Co. [2].
Sources: [1], [2], [3]
Caveats: Few, small trials. The lead author of the restriction trial was affiliated with Ajinomoto Co. [2]. The scoping review did not pool effect sizes [3].

Mixed results2

Moderate

Schizophrenia symptoms

Mixed results: a meta-analysis found lower symptoms with glycine added to antipsychotics, while the largest single trial found no effect on negative symptoms.

The numbers and sources

Effect: In a meta-analysis of 29 trials (1,253 cases) of NMDA receptor modulators added to antipsychotics, glycine reduced total symptoms (SMD -0.66). Added to non-clozapine antipsychotics, glycine reduced positive symptoms (SMD -0.54) and total symptoms (SMD -1.12) [4]. In the 16-week CONSIST trial of 157 patients with moderate to severe negative symptoms, glycine did not differ from placebo on negative symptom scores or cognition [5].
Population: Adults with chronic schizophrenia or schizoaffective disorder [4][5].
Sources: [4], [5]
Caveats: The meta-analysis notes small subgroup sizes [4]. The two sources disagree. CONSIST is the largest single glycine trial and found no general effect [5].

Limited

Glutathione and markers of aging (glycine with N-acetylcysteine)

Small trials found mixed results: one found GlyNAC improved glutathione and strength in older adults, and a larger trial found no rise in glutathione.

The numbers and sources

Effect: In 24 older adults, 16 weeks of glycine plus N-acetylcysteine (GlyNAC) against an alanine placebo improved glutathione deficiency, oxidative stress, mitochondrial function, insulin resistance, gait speed, strength and other measures [6]. In 114 healthy older adults given 2.4, 4.8 or 7.2 g a day for 2 weeks, GlyNAC did not raise the glutathione ratio (12.65 vs 12.49 with placebo, p = 0.739) or total glutathione (p = 0.278), the primary endpoint. A post hoc subgroup with high oxidative stress and low baseline glutathione showed increased glutathione [7].
Population: 24 older and 12 young adults [6]. 114 healthy older adults [7].
Sources: [6], [7]
Caveats: These test a combination, not glycine alone. The two trials disagree. Six authors of the larger trial were Nestlé employees, and Nestlé Health Science holds patents and markets GlyNAC products [7].

Doses studied

Sleep trials gave 3 g of glycine before bedtime [1][2]. GlyNAC trials used 2.4 to 7.2 g a day of the combined amino acids for 2 weeks [7], or a 16-week course [6]. Schizophrenia trials combined glycine with antipsychotic drugs [4][5].

Risks

Reported risks1

LimitedHow often is not known

Worsened symptoms when added to clozapine

Limited evidence: added to clozapine, glycine worsened positive symptoms in a small subgroup of trials.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: When added to clozapine, glycine worsened positive symptoms (SMD +0.56). None of the NMDA modulators tested showed benefit with clozapine [4].
Population: Clozapine-treated patients within a meta-analysis of 29 trials [4].
Sources: [4]
Caveats: Subgroup result with few trials [4].

Checked, no increase found1

Limited

Tolerability in trials

Limited evidence: GlyNAC was reported as well tolerated in small, short trials of older adults, which gave no adverse event counts.

The numbers and sources

How common: How often is not known: the sources give no rate.
Effect: GlyNAC was reported as well tolerated over 16 weeks [6] and at up to 7.2 g a day for 2 weeks [7].
Population: Older adults [6][7].
Sources: [6], [7]
Caveats: Small, short trials. The abstracts give no adverse event counts.

Claims tested and not found

That glycine improves negative symptoms or cognition in schizophrenia. CONSIST found no difference from placebo on negative symptoms or average cognition scores over 16 weeks [5].
That glycine and N-acetylcysteine raise glutathione in healthy older adults. The primary glutathione endpoints did not differ from placebo after 2 weeks [7].

Sources

Yamadera W, Inagawa K, Chiba S, et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms. 2007. https://doi.org/10.1111/j.1479-8425.2007.00262.x
Bannai M, Kawai N, Ono K, et al. The Effects of Glycine on Subjective Daytime Performance in Partially Sleep-Restricted Healthy Volunteers. Frontiers in Neurology. 2012. https://doi.org/10.3389/fneur.2012.00061
Fan Z, Nelson JM, Wallace TC. Glycine Bioavailability and Sleep-Related Outcomes Following Oral Glycine and Collagen Supplementation: A Scoping Review. Journal of Dietary Supplements. 2026. https://doi.org/10.1080/19390211.2026.2726197
Singh SP, Singh V. Meta-Analysis of the Efficacy of Adjunctive NMDA Receptor Modulators in Chronic Schizophrenia. CNS Drugs. 2011. https://doi.org/10.2165/11586650-000000000-00000
Buchanan RW, Javitt DC, Marder SR, et al. The Cognitive and Negative Symptoms in Schizophrenia Trial (CONSIST): The Efficacy of Glutamatergic Agents for Negative Symptoms and Cognitive Impairments. American Journal of Psychiatry. 2007. https://doi.org/10.1176/appi.ajp.2007.06081358
Kumar P, Liu C, Suliburk J, et al. 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. The Journals of Gerontology: Series A. 2023. https://doi.org/10.1093/gerona/glac135
Lizzo G, Migliavacca E, Lamers D, et al. A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage. Frontiers in Aging. 2022. https://doi.org/10.3389/fragi.2022.852569

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