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Also known as Glycine supplement
The simplest amino acid: an inhibitory brain messenger and a building block of collagen and glutathione. Human evidence is thin. Small trials report better sleep and less next-day tiredness with 3 g at bedtime, and one 74-person trial lowered HbA1c in type 2 diabetes, but a 2024 systematic review rates the sleep studies as small with a high risk of bias. 'GlyNAC' trials combine it with NAC, so they cannot show what glycine does alone.
We link to relevant studies and leave interpretation to you and your healthcare professional.
The large figures are what the studies reported for each thing they measured. Open a card for every result.
No figure given: Daytime sleepiness (unclear); Alertness test performance (reported a benefit); Tiredness (fatigue) (reported a benefit); Blood glycine levels (reported a benefit).
Every resultAssociated conditions and community-reported outcomes, wrapped together on one page. Aggregates appear only once enough reports arrive.
How this compound is sold in the UK, and where our readers typically find it.
Retailer search links — we may earn commission on purchases at no cost to you. Commission never affects our evidence ratings.
No figure given: Long-term blood sugar (HbA1c) (reported a benefit); Insulin response to glucose (reported a benefit); Insulin sensitivity (glucose disposal) (no clear benefit); TNF receptor I (inflammation marker) (reported a benefit).
No figure given: Divided attention (no clear benefit); Focused attention (no clear benefit); Mood (no clear benefit); Sustained attention (reported a benefit).
Every resultAudited published research for Glycine by condition. Drill into a pair page for the full breakdown.
Each bar counts published studies for this compound in that condition.
Where people report using it and what trials suggest
Common claims the trials do not support
Cheap amino acid with a plausible sleep mechanism seen in animals (it lowers core body temperature) but only small, short human trials; popular 'GlyNAC' longevity claims rest on combination studies with NAC.
Safety notes: Well tolerated at 3-5 g a day in trials; very high doses (tens of grams) caused nausea and poor taste-related adherence.
Evidence grades reflect study quality and consistency, not marketing claims.
Summaries of published trial results for this compound, grouped by condition. In these tables every number is exactly as the researchers published it. The headline figures above show a simple average where several studies measured the same thing in the same unit, and say so; nothing else is calculated or converted.
How to read this table
In short: benefit is what was observed; evidence is how much you should trust the observation. A “Benefit seen” tag on a weak study counts for far less than the same tag on a meta-analysis.
| Outcome measured | What trials found | Effect size | People studied | Duration | Type of evidence | Study |
|---|---|---|---|---|---|---|
| A1C levels | Glycine improved A1C levels compared with placebo in Seventy-four (3 months).Benefit seen | no number reported | Seventy-four | 3 months | RCT · 2008 | PMID 18852529 |
| Interferon-gamma level (rose with glycine, fell with placebo) | Glycine improved Interferon-gamma level (rose with glycine, fell with placebo) compared with placebo in Seventy-four (3 months).Benefit seen | no number reported | Seventy-four | 3 months | RCT · 2008 | PMID 18852529 |
| TNF-receptor I levels | Glycine improved TNF-receptor I levels compared with placebo in Seventy-four (3 months).Benefit seen | no number reported | Seventy-four | 3 months | RCT · 2008 | PMID 18852529 |
| Plasma glucose area response | Glycine improved Plasma glucose area response (> 50%) compared with glucose alone in Nine (2-h).Benefit seen | > 50% | Nine | 2-h | RCT · 2002 | PMID 12450897 |
| early insulin response | Glycine improved early insulin response (p < 0.05) compared with placebo in 12. (p < 0.05)Benefit seen | no number reported | 12 | — | RCT · 2001 | PMID 11456285 |
| insulin action | Glycine did not significantly improve insulin action compared with placebo in 12.No clear benefit | no number reported | 12 | — | RCT · 2001 | PMID 11456285 |
| late insulin response | Glycine improved late insulin response (p < 0.05) compared with placebo in 12. (p < 0.05)Benefit seen | no number reported | 12 | — | RCT · 2001 | PMID 11456285 |
| total insulin response | Glycine improved total insulin response (p < 0.02) compared with placebo in 12. (p < 0.02)Benefit seen | no number reported | 12 | — | RCT · 2001 | PMID 11456285 |
| Outcome measured | What trials found | Effect size | People studied | Duration | Type of evidence | Study |
|---|---|---|---|---|---|---|
| Divided attention | Bioglycin did not significantly improve Divided attention with no comparator reported.No clear benefit | no number reported | — | — | RCT · 1999 | PMID 10587285 |
| Focused attention | Bioglycin did not significantly improve Focused attention with no comparator reported.No clear benefit | no number reported | — | — | RCT · 1999 | PMID 10587285 |
| Mood | Bioglycin did not significantly improve Mood with no comparator reported.No clear benefit | no number reported | — | — | RCT · 1999 | PMID 10587285 |
| Retrieval from episodic memory | Bioglycin improved Retrieval from episodic memory with no comparator reported.Benefit seen | no number reported | — | — | RCT · 1999 | PMID 10587285 |
| Sustained attention | Bioglycin improved Sustained attention with no comparator reported.Benefit seen | no number reported | — | — | RCT · 1999 | PMID 10587285 |
| Outcome measured | What trials found | Effect size | People studied | Duration | Type of evidence | Study |
|---|---|---|---|---|---|---|
| Y-BOCS score change | Glycine improved Y-BOCS score change (6.04 points) compared with placebo in 14 (12 weeks).Benefit seen | 6.04 points | 14 | 12 weeks | RCT · 2009 | PMID 19046587 |
| Outcome measured | What trials found | Effect size | People studied | Duration | Type of evidence | Study |
|---|---|---|---|---|---|---|
| Sleep in healthy adults (small studies, high risk of bias) | Longer-term glycine administration improved Sleep in healthy adults (small studies, high risk of bias) with no comparator reported.Benefit seen | no number reported | — | — | Systematic review · 2024 | PMID 37851316 |
| Circulating glycine after glycine-containing supplements | Glycine-containing supplements improved Circulating glycine after glycine-containing supplements with no comparator reported.Benefit seen | no number reported | — | — | Study · 2026 | PMID 42687500 |
| Sleep-related outcomes in oral glycine trials | Oral glycine improved Sleep-related outcomes in oral glycine trials with no comparator reported.Benefit seen | no number reported | — | — | Study · 2026 | PMID 42687500 |
| Daytime fatigue after partial sleep restriction | Glycine (3 g before bedtime) improved Daytime fatigue after partial sleep restriction compared with placebo.Benefit seen | no number reported | — | — | Study · 2012 | PMID 22529837 |
| Daytime sleepiness after partial sleep restriction | Glycine (3 g before bedtime) showed an unclear effect on Daytime sleepiness after partial sleep restriction compared with placebo.Unclear | no number reported | — | — | Study · 2012 | PMID 22529837 |
| Psychomotor vigilance test performance |
| Glycine (3 g before bedtime) improved Psychomotor vigilance test performance compared with placebo.Benefit seen |
| no number reported |
| — |
| — |
| Study · 2012 |
| PMID 22529837 |