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Head-to-head evidence comparison — which supplement is right for you?
GABA vs Glycine: Glycine has the stronger overall evidence (6.5 vs 4/10); they're alternatives for perceived sleep quality — the best pick depends on your goals. Take the 60-second quiz for a pick tailored to your goals.
Glycine wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Too few graded studies
Top outcomes
Verdict
Too few graded studies
1 of 2 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both GABA and Glycine have evidence — compare verdict strength side-by-side.
250-300 mg (the one cited trial that states its dose used 300 mg a day). Label ranges go up to 750 mg, above that dose.
30-60 minutes before desired effect, Before bed for sleep, Before stressful events for anxiety
Capsules or powder
3g before bed (no cited trial states the dose it used)
30-60 minutes before bed
Powder (dissolves easily, tastes sweet)
30-60 minutes
30-60 minutes
30-60 minutes
First few nights
Next morning
Immediate
Herbal Remedies and Their Possible Effect on the GABAergic System and Sleep
Nutrients (2021) · Systematic review
A systematic analysis of studies on how various herbal medicines act on GABA receptor subtypes in the context of sleep. It reviews mechanisms, not trials of GABA supplements.
Effect of Probiotics on the Symptomatology of Autism Spectrum Disorder and/or Attention Deficit/Hyperactivity Disorder in Children and Adolescents: Pilot Study
Research on child and adolescent psychopathology (2025) · Rct · n=80
80 children aged 5 to 16 with ADHD (38) or autism (42) took a probiotic (Lactiplantibacillus plantarum and Levilactobacillus brevis, strains linked to dopamine and GABA production) or placebo for 12 weeks. No GABA was given.
GABA Supplementation, Increased Heart-Rate Variability, Emotional Response, Sleep Efficiency and Reduced Depression in Sedentary Overweight Women Undergoing Physical Exercise: Placebo-Controlled, Randomized Clinical Trial
Journal of dietary supplements (2024) · Rct · n=30
30 sedentary women with overweight or obesity doing physical exercise took GABA 200 mg or placebo once daily for 90 days.
The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review
GeroScience (2024) · Systematic review
The nervous system demonstrated the most positive effects, including improved psychiatric symptoms from longer-term glycine administration in psychiatric populations.
Glutamatergic drugs for schizophrenia
The Cochrane database of systematic reviews (2006) · Meta analysis · n=358
NMDA receptor co-agonists glycine and D-serine showed some effects in reducing the negative symptoms of schizophrenia (n=132, SMD -0.66, CI -1.0 to -0.3, p=0.0004), but the magnitude of the effect was moderate.
Ingestion of a Whey Plus Collagen Protein Blend Increases Myofibrillar and Muscle Connective Protein Synthesis Rates
Medicine and science in sports and exercise (2025) · Rct · n=28
In addition, myofibrillar protein synthesis rates were higher in BLEND compared with PLA in both the rested (0.038 ± 0.008 and 0.031 ± 0.006%·h -1 , respectively; P < 0.05) and exercised (0.052 ± 0.011 and 0.039 ± 0.009%·h -1 , respectively; P < 0.01) leg.
Glycine has a higher evidence score (6.5/10 vs 4/10) and wins in 2 of 3 categories.
For perceived sleep quality, Glycine has a higher relevance score (95 vs 62).
No documented interaction was found in the data searched. This does not establish that this exact combination is safe.
Ashwagandha, L-theanine, magnesium, saffron — what actually helps stress, and the safety caveats.
Melatonin, magnesium, glycine, L-theanine — tiered by evidence, plus a wind-down timeline.
When to take what, with or without food, and which supplements compete vs pair well.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.