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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
Probably helps
4 of 7 studies with measurable effects showed benefit.
Top outcomes
Shared outcomes (1)
Outcomes where both Glycine and Kava have evidence — compare verdict strength side-by-side.
3g before bed
30-60 minutes before bed
Powder (dissolves easily, tastes sweet)
150-300mg kavalactones daily
Evening for relaxation, 30-60 minutes before stressful events, Before bed for sleep
Water-extracted root powder or capsules
First night
Next morning
First night
Immediate
30-60 minutes
30-60 minutes
30-60 minutes
1-2 hours
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.
Herbal medicines in the treatment of psychiatric disorders: 10-year updated review
Phytotherapy research : PTR (2018) · Systematic review
Other encouraging herbal medicines with preliminary evidence include Curcuma longa (turmeric) in depression, Withania somnifera (ashwagandha) in affective disorders, and Ginkgo biloba (ginkgo) as an adjunctive treatment in Schizophrenia.
GABA-modulating phytomedicines for anxiety: A systematic review of preclinical and clinical evidence
Phytotherapy research : PTR (2018) · Systematic review
An open-ended search to 5 July 2017 was conducted using MEDLINE (PubMed), Scopus, and Cochrane library online databases and performed in a stepped format from preclinical to clinical investigations.
Herbal medicine for insomnia: A systematic review and meta-analysis
Sleep medicine reviews (2015) · Meta analysis · n=1602
There was no statistically significant difference between any herbal medicine and placebo, or any herbal medicine and active control, for any of the thirteen measures of clinical efficacy.
Based on systematic review showing nervous system benefits. Limited specific RCT data for sleep outcomes. Effects may vary significantly between individuals.
Based on multiple meta-analyses showing efficacy vs placebo with effect size comparable to benzodiazepines for mild-moderate anxiety. WS1490 extract showed OR=3.3 vs placebo. Effectiveness limited to 60% due to mixed results in some GAD populations and study quality limitations.
AI-estimated from published studies. Interpret as directional guidance.
Glycine has a higher evidence score (8.5/10 vs 9/10) and wins in 2 of 3 categories.
For improve deep sleep quality, Glycine has a higher relevance score (95 vs 55).
No known interactions between Glycine and Kava have been documented in our database. However, always consult a healthcare provider before combining supplements.