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Head-to-head evidence comparison — which supplement is right for you?
Glycine wins 2 of 3 categories. Both are solid choices — the best pick depends on your specific goals.
Verdict
Likely helps
6 of 6 studies with measurable effects showed benefit.
Top outcomes
Verdict
Likely helps
5 of 7 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (2)
Outcomes where both Glycine and Tryptophan have evidence — compare verdict strength side-by-side.
3g before bed
30-60 minutes before bed
Powder (dissolves easily, tastes sweet)
500-1000mg before bed
30-60 minutes before bed, On empty stomach or with carbohydrates
L-Tryptophan capsules
First few nights
Next morning
Immediate
30-60 minutes
1-2 weeks
1-2 weeks
1-2 hours after dose
The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review
GeroScience (2024) · Systematic review · n=34
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=132
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=14
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.
The Tryptophan Catabolite or Kynurenine Pathway in a Major Depressive Episode with Melancholia, Psychotic Features and Suicidal Behaviors: A Systematic Review and Meta-Analysis
Cells (2022) · Meta analysis · n=4647
Severe patients showed significant lower (p < 0.0001) TRP (standardized mean difference, SMD = -0.517, 95% confidence interval, CI: -0.735; -0.299) and TRP/CAAs (SMD = -0.617, CI: -0.957; -0.277) levels with moderate effect sizes, while no significant difference in CAAs were found.
Comparative efficacy and tolerability of nutraceuticals for depressive disorder: A systematic review and network meta-analysis
Psychological medicine (2025) · Meta analysis · n=17437
Adjunctive nutraceuticals consistently showed better efficacy than antidepressants (ADT) alone in outcomes including SMD, remission, and response.
Differential Metabolites in Osteoarthritis: A Systematic Review and Meta-Analysis
Nutrients (2023) · Meta analysis · n=495
In the 13 studies, 132 kinds of small molecule differential metabolites were extracted, 58 increased, 57 decreased and 17 had direction conflicts.
Based on systematic review showing nervous system benefits. Limited specific RCT data for sleep outcomes. Effects may vary significantly between individuals.
Based on meta-analyses showing tryptophan's role in depression and serotonin pathways. Evidence comes from studies of tryptophan depletion and kynurenine pathway research rather than direct supplementation RCTs. Conservative effectiveness due to indirect evidence.
AI-estimated from published studies. Interpret as directional guidance.
Glycine has a higher evidence score (6.5/10 vs 5.5/10) and wins in 2 of 3 categories.
For improve deep sleep quality, Glycine has a higher relevance score (95 vs 65).
No known interactions between Glycine and Tryptophan have been documented in our database. However, always consult a healthcare provider before combining supplements.