Pepdexpepdex
Stack
← All supplements

Glycine

Sleep

LimitedLittle human data, early, small, or narrow.

Simple amino acid studied for subjective sleep quality and next-day fatigue.

n≈7-15
Participant counts in the glycine sleep studies, the reason certainty here is low

What it is

The smallest amino acid, and a quietly interesting one: it is both a building block of collagen and an inhibitory neurotransmitter. That second role is why 3 g before bed shows up in sleep research, and why it tastes faintly sweet.

How it works

Rodent work suggests glycine acts on NMDA receptors in the brain's clock region to lower core body temperature, the same drop that naturally precedes sleep. The human mechanism is unconfirmed, and the human sleep studies are very small.

Which form to buy

Plain glycine powderThe studied form

The 3 g dose used in the Japanese sleep trials. Naturally sweet, dissolves in water.

Cheapest and exactly what was tested.

CapsulesConvenience

3 g means several capsules, bulkier and pricier than powder.

Fine, just less economical.

Collagen powderIncidental glycine

Glycine is ~a third of collagen's amino-acid RESIDUES but closer to ~26 g per 100 g by weight, so 10 g of collagen supplies roughly 2-2.6 g, not a clean 3 g. Hydrolysates vary.

A partial two-birds option if you already take it.

Magnesium glycinateNot this

The glycine there is a carrier for magnesium, the amounts are well below sleep-trial doses.

Do not count it as your glycine.

What it actually does, graded

Faster sleep onset & better sleep quality ratingsLimited

Very low certainty: the core studies ran roughly 15, 11 and just 7 analyzed participants, came from one manufacturer-linked research cluster, and a systematic review rated the healthy-population evidence high risk of bias.

Less next-day fatigue after poor sleepLimited

Shown in the same small trial set; promising, under-replicated.

Supports collagen synthesisLimited

Glycine is genuinely rate-limiting for collagen, but whether supplementing improves skin or joint outcomes has not been shown directly.

Metabolic or longevity benefitsNone shown

Interesting animal work, no human outcome evidence.

Pros and cons

Pros
  • Extremely cheap and pleasant to take
  • No sedation hangover, it is not a sedative, it is a temperature/onset effect
  • Clean safety profile at studied doses
Cons
  • The sleep evidence is a handful of tiny studies from one manufacturer-linked group, high risk of bias by systematic-review assessment
  • Effect is subtle, expect easier onset, not unconsciousness
  • Bulk powder dosing is less convenient than a pill

What to expect

  • The trials dosed 3 g about an hour before bed and measured subjective sleep quality the next morning.
  • What people report is falling asleep more easily rather than sleeping through, different from what melatonin or a sedative does.

Interactions

CautionClozapineOne 19-person trial at 30 g/day (ten times the sleep amount) suggested glycine might interfere with clozapine response. Nothing establishes this at 3 g, but it is worth a clinician flag.
MonitorSedatives and sleep medicationAdditive effects plausible, though glycine alone is not sedating.

Is it for you?

Probably worth it if
  • Trouble falling asleep specifically (rather than staying asleep)
  • You want to understand the cheapest low-risk option before anything stronger
  • You already take collagen and want the overlap explained
Probably skip it if
  • Your problem is waking at 3am, this addresses onset, not maintenance

Who should avoid it

  • Anyone taking clozapine

Research on this supplement

Papers about this supplement, not proof of the claims above. A title says what was studied, which is sometimes a negative result or a different question entirely.

  • The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review
    Geroscience, 2024
  • Glycine and N-acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genotoxicity, muscle strength, and cognition: Results of a pilot clinical trial
    Clin Transl Med, 2021

What the evidence says

A small number of human trials, mostly small and Japanese-industry funded, reporting better subjective sleep. Promising, not settled.

What studies used

The small published sleep studies used 3 g. Before bed.

Reported from published studies and product labelling — a record of what was used in research, not a recommendation. What is right for you is a conversation with a clinician.

Evidence base

S3,417 research papers
established literature

Large human evidence base: several phase 3 or 4 trial reports, plus multiple meta-analyses or systematic reviews.

This letter measures how much human research exists, not whether it works for you — the tier above (Limited) is the read on quality.

Research (12)

Turn Glycine into a plan that's yours

The info above is free. Membership makes it personal, the Coach answers questions about your exact stack, the Stack tracks it for you, and the Verified Sources shows you how to vet what you buy.

  • ✓ AI Coach, ask anything about your stack. It does the dosing math, flags interactions, and tells you what to do next.
  • ✓ Personal Stack, save your protocol, track it across devices, log doses, get a heads-up before a vial runs out.
  • ✓ Verified Sources, the vetted reference for checking quality and sourcing, members only.
Become a member, from $4.99/week

Cancel anytime · or save with $59.99/yr · Coach + Stack included

Where next

Every supplement in the catalogThe full shelf, grouped and evidence-tiered.→The compound indexSteroids, nootropics and research chemicals.→The peptide indexInjectable peptides and what trials used.→