5-HTP vs Glycine for sleep: which has better evidence?
A tie on evidence grade for sleep (5-HTP Grade C vs Glycine Grade C). For sleep, the two are evidence-matched; the difference is in effect and safety.
Platform evidence comparison
These existing platform assessments are separate from the source-reported findings below. They do not represent a direct trial comparing these treatments.
| 5-HTP | Glycine | |
|---|---|---|
| Grade | grade C | grade C |
| Certainty | low | low |
| Effect | limited evidence for sleep; serotonergic, so caution with antidepressants | small trials suggest improved subjective sleep quality and reduced next-day fatigue |
| Studied dose | — | 3 g before bed |
| Population | — | adults |
| Safety | 1 modeled interaction(s) | 0 modeled interaction(s) |
Grade C / low: hints of benefit in small trials; a well-run RCT could easily push this to B or to null.
Direct comparison evidence
There are no direct RCTs in our corpus comparing 5-HTP and Glycine head-to-head for sleep. What we present above is an indirect comparison: each side's own trials, contrasted. This is standard practice for supplement comparisons — dose, population, and outcome-instrument differences between the two evidence bases add uncertainty on top of each side's own grade.
Can you take both?
No modeled interaction between 5-HTP and Glycine in our corpus. Absence of a recorded interaction is not proof of additive benefit — combined-effect trials are usually absent for supplement pairs, so treat "stack" claims skeptically.
Decision guidance
- If certainty matters most — choose whichever side carries the higher certainty rating at a similar grade.
- If you're on medications — check each side's interaction pages before deciding; safety differences dominate small evidence-grade gaps.
- If your population is under-studied — the smaller-effect side with better population evidence often wins over the higher-grade side studied in a different demographic.
- If cost matters — form and dose page differences (5-HTP vs Glycine) can invert the practical winner.
Grade history
No grade changes yet. Initial grade assigned; re-reviewed on every 6 months (Grade C+) — next review by . Methodology v1.
Re-review cadence: every 6 months (Grade C+) · next scheduled by · methodology v1.
Frequently asked
Which has stronger evidence: 5-HTP or Glycine for sleep?
5-HTP carries Grade C at low certainty; Glycine carries Grade C at low. The stronger evidence points to a tie, subject to the caveat that direct head-to-head trials are usually absent for supplement pairings.
Can I take 5-HTP and Glycine together?
No modeled interaction between 5-HTP and Glycine; combining is not documented to be problematic, but combined-effect trials are also absent, so treat additive benefit claims skeptically.
Have 5-HTP and Glycine been compared head-to-head?
Direct RCTs comparing the two for sleep are uncommon. This page contrasts each side's own trial evidence — that is an indirect comparison, which introduces confounds from population and dose differences. See the direct-comparison block above.
What decides between 5-HTP and Glycine for me?
Read the decision guidance below — the split usually comes down to population fit, interaction risk with your other medications, and how much certainty you want behind the recommendation.
Related
Cite this page
Citation is encouraged. The proposed reuse license is CC-BY-4.0; status: pending-governance-ratification.
Plain-text citation
Substrate. 5-HTP vs Glycine for sleep. https://evidencebased.info/compare/5htp-vs-glycine-for-sleep. Updated 2026-07-14.
BibTeX
@misc{substrate_htpvsglycineforsleep,
author = {Substrate editorial},
title = {5-HTP vs Glycine for sleep},
year = {2026},
url = {https://evidencebased.info/compare/5htp-vs-glycine-for-sleep},
note = {evidencebased.info}
}