Glycine — Three Small Trials and One Company

My starting point

As with valerian, I start with what someone does before bed rather than what they take at bedtime. But I’ll say up front that I’m a fan of glycine.

Over the years, clients have told me it helped their sleep, taken at the trial amount before bed. A few took it during the day for anxiety and felt calmer. Some who took it alongside NAC thought they caught fewer colds. And a few who took it daily while we were tracking phthalates (plasticisers) on a urine test felt it helped them clear them.

That’s what people told me, not what a trial showed, and I hold the last one most loosely. Phthalates mostly leave the body within a day or so whatever you take. In one dosing study, two-thirds of a dose of the common plasticiser DEHP was in the urine within 24 hours (Koch et al., 2005). So a lower result on a repeat urine test mainly tells you about recent exposure, not about clearance.

I’m a fan of glycine in the same way I’m a fan of glutamine, creatine and NAC: the right thing, for the right person, at the right time, for the right reason. So here’s what the trials actually say.

What glycine is

Glycine is the simplest amino acid. Your body makes it, and you eat it in protein, especially in collagen-rich foods like skin, gristle, slow-cooked cuts and bone broth, because glycine is every third amino acid in collagen. It also works as a signalling molecule in the brain and spinal cord.

Does it help you sleep?

Grade: mixed. Three small trials, all positive on at least one outcome, all linked to the manufacturer, none repeated independently.

A 2026 review searched four databases for every trial of glycine supplements and sleep. It found three. All three reported a benefit on at least one sleep measure (Fan et al., 2026). A 2024 systematic review of glycine across the body reached a similar view: glycine improved sleep in healthy people, but "these studies had small sample sizes with a high risk of bias" (Soh et al., 2024).

The trials used 3 g of glycine before bed. Between them they reported:

• better self-rated sleep quality in people who said they slept poorly (Inagawa et al., 2006);
• in the one that measured sleep in a sleep lab, 11 adults who slept poorly fell asleep faster and reached deep sleep sooner on glycine than on a placebo, with no change in the overall shape of their sleep, and rated their sleep better. It was small, single-blind (the researchers knew which was which), with one recorded night on each, and several outcomes were tested without adjusting for that (Yamadera et al., 2007);
• after three nights of sleep cut by a quarter, less daytime fatigue and a better score on a reaction-time test the next day (Bannai et al., 2012).

Who paid? The researchers behind these trials worked for, or with, Ajinomoto, the Japanese company that makes glycine. Bannai and colleagues list Ajinomoto as their employer, and Bannai is also an author of the Yamadera trial, which was approved by Ajinomoto’s own review board. Ajinomoto sells glycine as a sleep product: in 2011 it launched Glysom, saying it had been "scientifically proven to promote deeper, sounder and more satisfying sleep" (Ajinomoto press release, 2011). That doesn’t make the results wrong. It means the whole evidence base comes from one company, and nobody independent has repeated it.

Compared with valerian: far fewer trials, but the ones that exist are more consistently positive. That’s a common pattern with young, single-source evidence. Valerian looked promising too, before the bigger independent trials arrived.

How it’s meant to work

Grade: mechanistic and untested in people (animal studies)

In rats, glycine taken by mouth acts on the brain’s body clock (the suprachiasmatic nucleus), increases blood flow to the skin and lowers core body temperature (Kawai et al., 2015). A drop in core temperature is part of how we normally fall asleep, so the idea is plausible. That work was done by Ajinomoto researchers with sleep scientists at Stanford.

What about collagen?

Collagen powders are sold for sleep partly because they’re rich in glycine.

• One small trial: 13 active young men with sleep complaints took 15 g of collagen peptides or a placebo before bed for a week. On collagen they woke less often during the night, but they didn’t fall asleep faster, sleep longer or sleep more efficiently (Thomas et al., 2024). Two authors worked for Rousselot, a collagen manufacturer.
• The 2026 review concluded that glycine is a plausible reason collagen might affect sleep, but that this "has not been directly tested" (Fan et al., 2026).

So if you already eat slow-cooked meat, fish with skin or a bone broth, you’re eating glycine. Whether more of it helps you sleep isn’t settled.

Who shouldn’t — and safety

Safety: few problems reported at 3 g; long-term safety data are thin.

• At 3 g, the trials reported few side effects. Higher doses can cause stomach upset and nausea.
• If you take antipsychotic medication, talk to your prescriber first. Glycine acts on the same brain receptor (the NMDA receptor) that has been studied as an add-on target in schizophrenia. In one trial, 60 g a day added to clozapine for eight weeks did no harm but also did nothing (Evins et al., 2000). It’s a reason for a conversation, not alarm.
• Pregnancy, breastfeeding and children: there are no safety data for glycine supplements. Food sources are fine.
• Kidney or liver disease: amino acid supplements are processed by both. Ask first.

How much: what the trials used

• Tested dose: 3 g of glycine before bed, taken 30 minutes before in the one trial that gives the timing (Bannai et al., 2012). The three trials were in people who said they slept poorly (Inagawa et al., 2006), 11 adults who slept poorly, with one recorded night on each (Yamadera et al., 2007), and healthy volunteers over three nights of sleep cut by a quarter (Bannai et al., 2012).
• Upper limit: no official upper limit; long-term safety data are thin.
• How long, and when to stop: the two trials that give a length ran one to three nights. Use the sleep diary below; if nothing has changed by the end of it, stop.
• Check first if: you take antipsychotic medicine, including clozapine; you are pregnant or breastfeeding, or it is for a child (no safety data); or you have kidney or liver disease.
• Grade: mixed. Three small trials, all linked to the manufacturer, none repeated independently.
• My practice, not trial-tested: a few clients have taken 1 g three times a day for anxiety. None of the trials above tested that amount, and I have no trial for it in anxiety.

The Test, Don’t Guess angle

There’s no useful test that tells you whether you need glycine. Blood glycine levels aren’t used to guide sleep treatment. So the test is a before-and-after sleep diary: two weeks as you are, then two to four weeks with the tested amount before bed (see How much above), noting how long you take to fall asleep, how often you wake, and how you feel at 3pm. If nothing changes, stop.

And if your sleep problem has lasted months, the treatment with the best evidence is still cognitive behavioural therapy for insomnia (CBT-I), available through the NHS. See last month’s valerian piece for more on that.

The bottom line

• Does it work? Maybe, a little. Three small trials say yes, all from the company that makes it.
• Is it safe? At the tested amount, for most adults in the short term, it appears to be. Check first if you take antipsychotic medication or are pregnant.
• Food first: slow-cooked cuts, fish skin and broth already supply it.
• Test it on yourself with a diary, and stop if nothing changes.

This month’s recipe is an alcohol-free evening drink, built for the same wind-down hour: The Nightcap Without the Alcohol.

Sources

PubMed records resolved and abstracts checked 5 October 2026.

Ajinomoto Co., Inc. Ajinomoto Co., Inc.’s twofold nutraceutical solution targets weight management and sleep quality improvement. Press release, PR Newswire, 11 October 2011.

Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol 2012;3:61. PMID 22529837. doi:10.3389/fneur.2012.00061

Evins AE, Fitzgerald SM, Wine L, Rosselli R, Goff DC. Placebo-controlled trial of glycine added to clozapine in schizophrenia. Am J Psychiatry 2000;157(5):826–828. PMID 10784481. doi:10.1176/appi.ajp.157.5.826

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;23(5):602–622. PMID 42687500. doi:10.1080/19390211.2026.2726197

Inagawa K, Hiraoka T, Kohda T, Yamadera W, Takahashi M. Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep Biol Rhythms 2006;4(1):75–77. doi:10.1111/j.1479-8425.2006.00193.x

Kawai N, Sakai N, Okuro M, et al. The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology 2015;40(6):1405–1416. PMID 25533534. doi:10.1038/npp.2014.326

Koch HM, Bolt HM, Preuss R, Angerer J. New metabolites of di(2-ethylhexyl)phthalate (DEHP) in human urine and serum after single oral doses of deuterium-labelled DEHP. Arch Toxicol 2005;79(7):367–376. PMID 15700144. doi:10.1007/s00204-004-0642-4

Soh J, Raventhiran S, Lee JH, et al. The effect of glycine administration on the characteristics of physiological systems in human adults: a systematic review. GeroScience 2024;46(1):219–239. PMID 37851316. doi:10.1007/s11357-023-00970-8

Thomas C, Kingshott RN, Allott KM, et al. Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints. Eur J Nutr 2024;63(1):323–335. PMID 37874350. doi:10.1007/s00394-023-03267-w

Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms 2007;5:126–131. doi:10.1111/j.1479-8425.2007.00262.x