Last updated: October 2026
Glycine is an amino acid that may help some people sleep a little better, but the evidence is thin. A handful of small Japanese studies gave 3g before bed and found people rated their sleep and next-day tiredness better. It isn’t a proven sleep aid, it has no authorised health claims, and it won’t fix ongoing insomnia.
Below: what the research actually shows, how much and when people take it, side effects, how it compares with magnesium glycinate, and food sources.
What is glycine?
Glycine is the smallest amino acid. Your body makes it, and you also get it from protein foods, especially collagen and gelatine. In the brain and spinal cord it works as a signalling molecule, which is why researchers became interested in it for sleep.
The leading idea, mostly from rat studies, is that glycine nudges blood flow towards the skin, so core body temperature drops slightly. A small fall in core temperature is part of how the body normally winds down for sleep. In rats, this effect ran through the brain’s body clock (the suprachiasmatic nucleus). Whether the same happens in people at a 3g dose isn’t proven.
Does glycine help you sleep?
Possibly, a little, for some people. The human evidence comes down to three small trials, all using about 3g before bed:
| Study | Who took part | What it reported |
|---|---|---|
| Inagawa and colleagues, 2006 (Sleep and Biological Rhythms) | Volunteers unhappy with their sleep | People rated how they felt on waking (fatigue, clear-headedness) better than with placebo |
| Yamadera and colleagues, 2007 (Sleep and Biological Rhythms) | Volunteers with ongoing unsatisfying sleep | Better self-rated sleep quality, with overnight lab sleep recordings that moved in the same direction |
| Bannai and colleagues, 2012 (Frontiers in Neurology) | Healthy men with sleep cut by 25% for three nights; 7 analysed | Less fatigue on day one and faster reaction times; most other measures showed no difference |
That is a very small evidence base. A 2026 scoping review that searched the main medical databases found only these three glycine sleep trials. All three reported a benefit on at least one sleep-related measure, but the authors called for larger trials.
Things to weigh up:
- Tiny numbers. The 2012 study analysed just seven men.
- Short. Days, not months.
- Industry links. Much of the research was run by scientists at Ajinomoto, a Japanese amino acid company. That doesn’t make it wrong, but independent trials are missing.
- Mostly how people felt. Many results are self-rated, which placebo can sway.
Our honest take: glycine is a reasonable, low-cost thing to try alongside good sleep hygiene, not instead of it. For how it stacks up against other options, see natural sleep aids ranked by evidence.
How much glycine for sleep?
The studies used 3g. There is no evidence that more works better.
If you try it, start at 3g or below, give it a week or two and judge honestly whether your sleep or mornings feel any different. A simple sleep calculator or diary helps here.
When to take glycine for sleep
In the studies, people took it shortly before bed: the 2012 trial gave it about 30 minutes before bedtime. Taking it as part of a regular wind-down, at the same time each night, fits with how it was tested. For more on timing, see how to fall asleep fast.
Glycine side effects and who should check first
Glycine was generally well tolerated in the sleep studies, and the 2012 trial reported no side effects. But the trials were tiny and short, so long-term safety at supplement doses isn’t well studied. If you get stomach upset, stop.
- If you take any prescribed medicines, or have a kidney, liver or mental health condition, check with your GP or pharmacist first.
- There isn’t enough evidence on glycine supplements in pregnancy or breastfeeding. We don’t recommend our products during pregnancy or breastfeeding.
- Supplements are for adults only.
The NHS advises seeing a GP if changing your sleep habits hasn’t helped, you’ve had trouble sleeping for months, or it’s making daily life hard to cope with. Loud snoring with pauses in breathing, or waking unrefreshed every day, also needs checking. See insomnia and why you wake up tired.
Glycine vs magnesium glycinate
They are not the same thing. Magnesium glycinate (also called bisglycinate) is magnesium bound to two glycine molecules. It is mainly a way of taking magnesium, and the glycine it carries is small next to the 3g used in sleep studies.
Rough maths: magnesium makes up about 14% of magnesium bisglycinate by weight, so each 100mg of magnesium from bisglycinate comes with roughly 0.6g of glycine. Even 400mg of magnesium, the NHS upper guide for supplements, would supply only about 2.5g. These figures are approximate and assume fully reacted bisglycinate.
| Glycine | Magnesium glycinate | |
|---|---|---|
| What it is | An amino acid | Magnesium bound to glycine |
| Typical amount studied for sleep | 3g before bed | Dosed by magnesium, usually 100mg to 400mg |
| Glycine per dose | 3g | Roughly 0.6g per 100mg magnesium (approximate) |
| Authorised health claims | None | Yes, for magnesium, e.g. contributes to the reduction of tiredness and fatigue |
Magnesium contributes to normal functioning of the nervous system and normal psychological function. For whether magnesium itself helps sleep, see magnesium for sleep, and for timing, the best time to take magnesium. Comparing forms? Read glycinate vs citrate vs threonate.
Some people take glycine and magnesium together. There is no research on the combination for sleep, so treat it as personal experiment rather than evidence.
Our evening magnesium drink
Our Magnesium Glycinate Sleep Complex is a berry powder with magnesium bisglycinate and citrate (148mg magnesium per serving), plus added glycine, L-theanine, chamomile, passionflower, hops and oat straw. Magnesium contributes to the reduction of tiredness and fatigue. It is not a 3g glycine dose, and we don’t claim its glycine improves sleep: it is simply a warm or cold drink for your evening routine. For the other ingredients, see L-theanine and passionflower for sleep.
Food sources of glycine
Most people already get a few grams of glycine a day from food. The richest sources are collagen-rich foods:
- Gelatine: about 19g of glycine per 100g of dry powder in USDA data, so a 10g spoonful has roughly 1.9g.
- Bone broth and slow-cooked cuts with skin and connective tissue.
- Meat and poultry: roast chicken breast has about 1.5g per 100g.
- Fish: cooked farmed salmon has about 1g per 100g.
Food alone rarely gets you a concentrated 3g at bedtime, which is why the studies used powder. If you’re comparing other bedtime options, see sleep capsules, melatonin in the UK and the best teas for sleep.
Glycine for sleep: FAQs
Does glycine help you sleep?
It may help a little. Three small studies giving 3g before bed reported better self-rated sleep or next-day tiredness, but they were tiny, short and mostly industry-run.
How much glycine should I take for sleep?
The studies used 3g, taken shortly before bed. There is no evidence that larger amounts work better.
How long before bed should I take glycine?
In the studies it was taken shortly before bed, about 30 minutes beforehand in the 2012 trial.
Is glycine the same as magnesium glycinate?
No. Magnesium glycinate is magnesium bound to glycine. Each 100mg of magnesium from it carries only roughly 0.6g of glycine, well below the 3g used in sleep studies.
Does glycine have side effects?
It was generally well tolerated in the small studies. Stop if you get stomach upset, and check with your GP or pharmacist first if you take medicines or have a kidney, liver or mental health condition.
Can I take glycine every night?
The studies only lasted days, so long-term nightly use hasn’t been well studied. If sleep problems last for months, see your GP rather than relying on a supplement.
Sources
- Bannai M, Kawai N, et al. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012. PMID 22529837.
- Yamadera W, Inagawa K, et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5:126 to 131.
- Inagawa K, Hiraoka T, et al. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms. 2006;4:75 to 77.
- Fan Z, Nelson JM, Wallace TC. Glycine bioavailability and sleep-related outcomes following oral glycine and collagen supplementation: a scoping review. J Diet Suppl. 2026. PMID 42687500.
- Kawai N, et al. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology. 2015. PMID 25533534.
- NHS. Vitamins and minerals: others (magnesium).
- NHS. Insomnia.
- USDA FoodData Central: Gelatins, dry powder, unsweetened (FDC ID 169599); chicken breast, roasted (171477); Atlantic salmon, farmed, cooked (175168).
This guide is general information, not medical advice. Evopure makes the Magnesium Glycinate Sleep Complex.
