Glycine

Supplements · Amino Acids · Supplement, Typed Supps

A simple amino acid that happens to have a calming effect.

Stage by stage

Intake (Powder or capsule): Absorbed simply in the small intestine as a basic amino acid.
Small intestine (Absorbed): Absorbed simply in the small intestine as a basic amino acid.
Bloodstream (Widely used): Used broadly in protein synthesis throughout the body.
Brain & spinal cord (Calming neurotransmitter): Acts as a calming neurotransmitter, and may slightly lower core body temperature.

What the evidence supports

Improving subjective sleep quality when taken before bed — limited evidence. A few small trials, mostly from one research group, report better sleep quality and less daytime tiredness at 3 g. Promising and cheap; not well replicated.
Supporting collagen synthesis — moderate evidence. Glycine is a third of collagen by residue count and can be rate-limiting. Whether supplementing changes any outcome you would notice is a separate question.
Improving metabolic health or longevity — insufficient evidence. An active research area with interesting animal data and very little human evidence.

Typical dose

3 g about an hour before bed in the sleep trials

Upper limit: No formal UL. Schizophrenia trials have given far larger amounts — 60 g daily for eight weeks — without safety problems, so the 3 g used for sleep sits a long way below anything that has caused trouble

Timing

Typically taken shortly before bed.

Time to effect

Same night: Effects, if any, are usually felt immediately.

Medication interactions

Clozapine: Glycine acts at the NMDA receptor glycine site and has been trialled as a clozapine add-on; it did not help and there is a long-standing concern it works against clozapine's benefit in some people. Do not add it without your prescriber's knowledge. (moderate)

Common myth

“Glycine is a sedative drug.” In reality: It’s a common amino acid found in food; its sleep effect works through normal calming pathways.