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Head-to-head evidence comparison — which supplement is right for you?
Glycine vs Tryptophan: Glycine has the stronger overall evidence (6.5 vs 5.5/10); 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
1 of 2 studies with measurable effects showed benefit.
Top outcomes
Verdict
Likely helps
3 of 3 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 (no cited trial states the dose it used)
30-60 minutes before bed
Powder (dissolves easily, tastes sweet)
500-1000 mg before bed. The cited sleep meta-analysis found the benefit mainly at 1 g a day or more.
30-60 minutes before bed, On empty stomach or with carbohydrates
L-Tryptophan capsules
and 2 more not shown
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
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.
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
Hundred and ninety-two trials involving 17,437 patients and 44 nutraceuticals were eligible for inclusion.
Differential Metabolites in Osteoarthritis: A Systematic Review and Meta-Analysis
Nutrients (2023) · Meta analysis · n=495
A systematic review and meta-analysis of 13 studies with 495 participants comparing small-molecule metabolites in people with osteoarthritis against healthy people. No supplement was tested.
Glycine has a higher evidence score (6.5/10 vs 5.5/10) and wins in 2 of 3 categories.
For perceived sleep quality, Glycine has a higher relevance score (95 vs 65).
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.
When to take what, with or without food, and which supplements compete vs pair well.
Melatonin, magnesium, glycine, L-theanine — tiered by evidence, plus a wind-down timeline.
The right pick depends on your goals. Answer a few quick questions for a personalised recommendation — or dig into the full evidence on each.