Glycine

Three grams of glycine before bed improved how people felt about their sleep in a few tiny Japanese trials, most run by a glycine maker. Promising, but far from proven.

• Evidence: Weak
• Low effort
• Low cost
• Works: 1–3 nights in trials

Why it matters

Glycine is an amino acid. Your body makes it, and you also get it from protein foods. The researchers who studied it for sleep think it works by helping your core body temperature drop at night: in rats, oral glycine increased blood flow to the skin and lowered core temperature [5]. A falling core temperature is part of how you fall asleep. That’s a plausible mechanism, but most of it comes from animal work.

How to do it

1. Dose used in trials: 3 g. All the sleep trials in healthy people used 3 g a night [4].
2. Timing: 30–60 minutes before bed. Trials gave it between 30 minutes and 1 hour before bedtime [4].
3. Take it for a few nights, then judge. The trials lasted 2 to 4 nights [4]. Nobody has tested whether the effect lasts over months.
4. Don’t go higher. Studies that gave much larger single doses (around 0.8 g per kg of body weight) found worse attention and cognitive performance in healthy people [4].
5. Keep a simple sleep diary. Note how long it took to fall asleep and how alert you felt in the morning, with and without glycine.

Check with a doctor or pharmacist first if you’re pregnant or breastfeeding, or take any regular medication. In the US, the FDA doesn’t approve dietary supplements before they’re sold; the maker is responsible for safety and labeling [7].

Side effects and interactions

The sleep trials were too small and short to judge safety, and we found no official fact sheet (such as from the NIH) on glycine supplements.

• Antipsychotics: in a trial of 19 people with schizophrenia on clozapine, very high doses of glycine (30 g a day) seemed to stop the medicine working as well [6]. If you take clozapine or another antipsychotic, don’t add glycine without asking your psychiatrist.
• Sleeping pills, sedatives, antidepressants, blood pressure medication: we found no studies of glycine combined with these. That’s a gap in the evidence, not proof of safety, so ask your pharmacist.

Common mistakes

• Reading “improved sleep quality” as “more sleep”. In the trial that measured sleep in a lab, glycine shortened the time to fall asleep and to reach deep sleep, but the overall structure of sleep didn’t change [1].
• Taking it to cover for short sleep. In one trial, people slept 25% less than usual for three nights and felt less tired with glycine [2]. Feeling less tired doesn’t undo the effects of short sleep.
• Trusting the big claims online. They trace back to the same few small studies.

Effect on your sleep score

• Time to fall asleep: shorter in a sleep-lab trial of 11 people [1] [4]. The paper we could read doesn’t give the size in minutes.
• Deep sleep: people reached deep sleep sooner, but the amount of each sleep stage didn’t change [1].
• Efficiency: better in the same trial [1].
• HRV, resting heart rate, total sleep: we found no study measuring these in healthy adults with wearables.

How confident: low. Your tracker may show no change at all.

Evidence

Rated Weak. Three small crossover trials (each person tried both glycine and placebo) are the main evidence:

• Inagawa 2006: 19 people unhappy with their sleep, 3 g a night for 4 nights. Better self-rated sleep [3] [4].
• Yamadera 2007: 11 people with ongoing poor sleep, 3 g an hour before bed for 2 nights. Better self-rated sleep, faster sleep onset in the lab, less daytime sleepiness [1] [4].
• Bannai 2012: 10 healthy men enrolled and only 7 analyzed, with sleep cut by 25% for three nights. Less fatigue and better reaction-time scores the next day [2].

A 2024 systematic review concluded that the sleep studies had small samples and a high risk of bias [4].

Industry funding: researchers from Ajinomoto, a company that makes glycine, co-authored the Yamadera trial and ran the Bannai trial [1] [2]. In the Bannai trial, the participants were the company’s own employees, and the company’s review board approved it [2]. Three of the Yamadera authors also wrote the Inagawa trial [3]. That doesn’t make the results wrong, but independent trials haven’t confirmed them.

General information for healthy adults, not medical advice. If you have a sleep problem that lasts, read when to see a doctor. Sources checked 4 October 2026. Spot a mistake? Tell us.