Glycine

What it is

Glycine is the simplest amino acid and makes up about a third of collagen. Your body makes it, and food sources include meat, fish, gelatine and bone broth.

Supplements are taken mostly for sleep quality, and sometimes for joint, skin or metabolic goals. It tastes slightly sweet, which is where the name comes from.

It is also used alongside NAC in research on glutathione.

How it works

Glycine acts as an inhibitory neurotransmitter in the brain and spinal cord. Taken before bed it may lower core body temperature slightly, which is linked with easier sleep onset. It is also one of the three building blocks of glutathione.

What the evidence says

• Moderate Subjective sleep quality
  Small trials in people with poor sleep report better feeling of rest; sample sizes are small.
• Limited Daytime sleepiness and performance after poor sleep
  Small studies suggest modest improvement.
• Limited Glutathione support
  Glycine may be limiting in older adults; combined with NAC it raised glutathione in small trials.
• Limited Blood sugar control
  Small, early studies only.
• Weak Joint and skin benefits
  Mostly inferred from collagen biology rather than direct trials.

Evidence ratings are our plain-English summary of how much good human research exists, not a promise of results. How we rate evidence.

Dosage and timing

• Sleep studies typically use 3 g taken before bed.
• Higher doses of 5 to 10 g are used in other research, usually split.
• Dissolve the powder in water; it is mildly sweet.
• Check current guidance if using high doses long term.

Forms and what to look for

• Glycine powder is cheapest and easy to mix.
• Capsules require many to reach 3 g.
• Collagen and gelatine contain glycine but at lower amounts per serving.
• Choose single-ingredient products with a clear dose.

What to expect, and when

• Sleep effects, if any, are noticed within a few nights.
• Other uses would need weeks and may show nothing noticeable.

Side effects

• Generally well tolerated.
• Mild nausea or soft stools at higher doses.
• Sleepiness or lightheadedness.
• Rarely, stomach discomfort.

Interactions

• Clozapine: glycine may reduce its effect; speak to a prescriber.
• Sedatives and sleep medicines: additive drowsiness is possible.
• Other glycine-containing or NAC supplements: generally fine but combine with care.

Who should avoid it

• People taking clozapine without clinician input.
• Anyone with kidney or liver disease: check first.
• Pregnant or breastfeeding people: limited data on supplemental doses.
• People with persistent insomnia should see a GP rather than rely on supplements.

Risks and safety

• Very high doses are not well studied.
• Not banned by WADA.
• Contamination is a general supplement risk.

Buying well: quality and testing

• Single-ingredient powder with clear dose.
• Food or pharmaceutical grade labelling.
• Third-party tested if you compete.
• Avoid sleep blends that hide the glycine amount.

Bottom line

Glycine is cheap, mild and low risk, which makes a 3 g trial before bed a reasonable experiment if sleep is mediocre. Evidence is small, so treat it as an experiment. Ongoing sleep problems deserve a conversation with a GP.