Glycine powder: what it does and where it's found

What is glycine powder?

Glycine powder is pure glycine, the smallest of the amino acids that make up protein. It comes as a white powder that dissolves easily in water and tastes sweet, which is how it got its name: glykys is Greek for sweet. Most products suggest 3 g a serving, the amount used in a handful of Japanese sleep trials described below. A glycine supplement in capsules holds the same amino acid; powder is easier for gram-sized doses, because a capsule holds much less.

In the UK glycine is sold as a food supplement. Great Britain's register of nutrition and health claims has no authorised claim for it, so no glycine product can legally promise to improve your sleep, skin, joints or anything else.

What does glycine do in the body?

Glycine is a building block for proteins and for several other molecules your body makes. A 2017 review lists, among others:

• collagen, the main structural protein in skin, tendons and bone, where every third amino acid is glycine
• creatine (our guide to taking creatine covers the supplement)
• glutathione
• haem, the iron-containing part of the haemoglobin in red blood cells
• purines, which form part of DNA and RNA
• bile salts, which help you digest fat

Glycine is also a messenger in the nervous system. It dampens nerve signals through glycine receptors, and it helps switch on another set of receptors (NMDA receptors) that respond to glutamate.

You don't have to get glycine from food, because the body makes it, mostly from serine. A 2009 paper argued, from calculations rather than from trials, that what the body makes plus what you eat may fall short of what it uses, mostly for collagen. Nobody has tested that idea in people. And these are jobs glycine does in the body, which isn't evidence that extra glycine from a supplement helps with any of them.

Is L-glycine different from glycine?

No. Most amino acids come in mirror-image L and D forms, but glycine is too simple a molecule to have either. "L-glycine" on a label means plain glycine, so it isn't worth paying extra for.

What does a glycine supplement do?

It raises the glycine level in your blood, and there's little proof of what that does for your health. A 2026 scoping review found 14 pharmacokinetic trials in which glycine-containing supplements generally raised circulating glycine, with some sign that larger doses raised it more. For sleep, the same review found only three trials of glycine on its own, and its authors said that whether glycine causes the sleep effects seen with glycine and collagen supplements has not been directly tested. A 2026 review of amino acid supplements adds that the long-term effects of supplementing are still unknown, that you shouldn't exceed safe upper levels, and that medical supervision is advisable if you have an existing metabolic or physiological problem. No health claim is authorised for glycine in Great Britain, so a product can't promise a benefit.

Glycine-rich foods: which foods are high in glycine?

Every protein food contains some, but gelatine and foods with skin or connective tissue are far richer than the rest, because one in every three amino acids in collagen is glycine. Published estimates of what a typical diet supplies range from about 1.5 g to 5 g a day.

The figures come from the US Department of Agriculture's FoodData Central database, scaled to the portions shown and rounded, so UK products will differ a little. Stock and bone broth made with bones, skin and joints contain gelatine, but the amount varies too much to give a useful figure. If you eat little or no meat, soya, seeds, peanuts and pulses still supply some glycine, and your body makes the rest. Collagen supplements are rich in glycine too; our collagen guide covers what they do and don't do.

Does glycine help you sleep?

The evidence is thin. Three small trials gave volunteers 3 g of glycine before bed, and scientists at Ajinomoto, a Japanese amino acid manufacturer, ran all three:

• 19 women who said they slept poorly took glycine and a placebo in random order. They reported feeling less tired the next morning after glycine.
• 11 adults with long-standing sleep complaints were monitored overnight in a single-blind crossover trial. On glycine they fell asleep, and reached deep sleep, sooner, and they rated their sleep better.
• 10 healthy men, all Ajinomoto employees, had their sleep cut by a quarter for three nights. On glycine they reported less fatigue and did better on an alertness test.

A 2026 scoping review found only these three trials of glycine supplements and sleep. All three reported a benefit on at least one measure, and the reviewers called for larger trials. We couldn't find an independent trial that has repeated the results. Because no claim is authorised, a glycine product sold in Great Britain may not say it helps you sleep. For what is known to help, see our guide to magnesium and sleep, which sets out the NHS's sleep advice.

How do you take glycine powder?

The sleep trials used 3 g dissolved in water shortly before bed. Use the scoop that comes with the product or weigh it, because a heaped spoon can hold more than you think. It dissolves quickly and tastes mildly sweet, so water or a hot drink both work. Capsules are less practical: a 3 g dose takes six 500 mg capsules.

Larger doses have been tested. A review by the Ajinomoto group reported no adverse effects when 12 volunteers took 9 g during the day, and no serious side effects at 31 g a day. Trials in schizophrenia used 30 to 60 g a day for 8 to 12 weeks. None of that is a reason to take more than the label says.

Is glycine safe? Side effects and who should avoid it

At 3 g a day, the short trials in healthy adults reported no serious side effects. Take more care in these cases:

• If you take clozapine, or any antipsychotic, don't take glycine unless your psychiatrist or mental health team agrees. In a 1999 trial, 19 people with schizophrenia who were taking clozapine added 30 g of glycine a day or a placebo for 12 weeks. Positive symptoms fell by 35% in the clozapine-plus-placebo group but didn't improve with glycine, and the researchers suggested glycine may interfere with clozapine. A 2000 trial of 60 g a day found no benefit and no worsening.
• If you're pregnant or breastfeeding, ask your midwife or GP first, because glycine supplements haven't been studied in either.
• If you plan to take it for months or years, bear in mind that the trials lasted only days or weeks.
• If you take regular medicines or have a long-term condition, ask a pharmacist to check first.

How to choose a glycine supplement in the UK

No single product suits everyone. Look for:

• A label that says food supplement. Glycine is also sold as a laboratory chemical, which isn't made or checked to food standards.
• The amount of glycine per serving, and whether it's glycine alone or a blend.
• No melatonin, which is a prescription-only medicine in the UK, so a food supplement sold here shouldn't contain it.
• No promises about sleep, skin or joints, which GB rules don't allow for glycine.
• Independent testing for purity, which is worth looking for in any supplement.

Where Natura fits

Daily Glycine, in the Natura cabinet (coming soon), is a 3 g serving of glycine powder. It's also one of the four bottles in the Sleep Pack, which is not a sleeping tablet and contains no melatonin, and it's in our Protein Pack, so take only one product that contains it. Glycine has no authorised health claim, so we don't claim it helps you sleep or does anything else for you, and the trials above aren't evidence for our product.