Myths About Glycine

Glycine is one of the cheapest and best-known amino acids: some consider it a 'cure for stress,' others a complete dud. The editorial team examined the five most common claims about glycine and compared them with research findings to separate real effects from marketing.

Where the myths about glycine came from

Glycine is the simplest amino acid: in its molecule, instead of a side chain there is only a hydrogen atom. Despite this modest structure, it performs dozens of functions in the body - from building collagen to transmitting nerve impulses. It is precisely this versatility that became the ground for myths: when a substance 'takes part in everything,' it is easy to attribute to it the ability to 'affect everything.'

In the post-Soviet region, glycine has been sold in pharmacies for decades as a cheap 'nerve' remedy in the form of 100 mg tablets placed under the tongue. This status shaped many people's perception of it as a mild nootropic and sedative. Meanwhile, in the Western sports industry glycine was rediscovered - as a supplement for sleep, joints, and glutathione synthesis, already in doses of several grams.

Two traditions - the pharmacy one and the sports-nutrition one - gave rise to contradictory perceptions. Some consider glycine a universal 'cure for stress,' others a dud that the body synthesizes on its own anyway. The editorial team examined the most common claims and compared them with what studies have actually shown.

It is worth noting right away: the evidence base for glycine as a supplement is small. Most human studies involve small samples, are often sponsored by manufacturers, and many effects have been demonstrated only in animals. So the honest answer to a significant portion of the questions is 'maybe, but there is little data.'

Myth 1: a tablet under the tongue relieves stress

The most widespread belief is that one or two 100 mg glycine tablets under the tongue quickly calm you down and improve concentration before an exam or an important event. In practice, there are virtually no convincing independent randomized studies in the international literature that would confirm such an effect of precisely these doses in healthy people.

The problem is scale. A person gets several grams of glycine from their diet every day, and the body also synthesizes it from serine and other precursors. Against this background, 100 mg is a very small supplement. Sublingual intake does not make it 'more powerful' either: glycine is a small water-soluble molecule that is well absorbed in the intestine anyway.

Studies that recorded changes in well-being used much higher doses - around 3 g before bed. In the work of Bannai and colleagues (2012), participants with restricted sleep reported less fatigue and better daytime performance after such intake. But this is a different dose, a different aim, and a different mechanism than a 'pill for nerves.'

The feeling of calm after a tablet may be real for a particular person, but it is largely explained by expectation and the ritual of taking it. This does not mean glycine is harmful - only that from pharmacy doses one should not expect a pharmacological effect comparable to anxiolytics.

Myth 2: glycine is a sleeping pill

The opposite extreme is the belief that a few grams of glycine work like a sleeping drug. The study by Yamadera and colleagues (2007) did indeed show that 3 g of glycine before bed improved subjective sleep quality and shortened the time to fall asleep, while polysomnography recorded a faster entry into deep sleep stages. However, this is about a moderate improvement, not sedation.

The mechanism proposed by Japanese researchers in animal models (Kawai et al., 2015) is linked to an effect on NMDA receptors in the suprachiasmatic nucleus of the hypothalamus. This leads to dilation of peripheral blood vessels and a drop in core body temperature, and such a drop is one of the natural signals for falling asleep.

Glycine does not suppress the respiratory center, does not cause dependence of the benzodiazepine type, and does not produce pronounced morning drowsiness. But it also does not 'switch off' a person suffering from chronic insomnia. For clinical insomnia, the first line of treatment remains cognitive behavioral therapy and working with a doctor.

• What has been shown:improvement in subjective sleep quality and daytime well-being in small studies.
• What has not been shown:effectiveness in chronic insomnia, comparability with sleeping medications.
• What is important to remember:sleep hygiene, routine, and caffeine in the evening have a stronger effect than any amino acid.

So glycine can be regarded as a mild auxiliary aid within overall sleep hygiene, but not as a substitute for treatment.

Myth 3: glycine helps build muscle

In the sports community you sometimes encounter the claim that glycine is an 'anabolic amino acid' because it is part of creatine and proteins. Indeed, glycine, together with arginine and methionine, is a precursor of creatine in the liver and kidneys. But this does not mean that extra glycine increases creatine stores in the muscles: synthesis is regulated by enzymes, not by the availability of raw material.

For stimulating muscle protein synthesis, the key role is played by leucine and the total amount of essential amino acids. Glycine is not among the essential ones, and there are no studies that would show a gain in muscle mass in healthy people from taking it. A protein supplement or ordinary food with enough protein is a far more effective strategy.

A more interesting direction is connective tissue. Collagen is roughly one-third glycine, and the hypothesis of Melendez-Hevia and colleagues (2009) suggests that endogenous glycine synthesis may not be enough for optimal collagen renewal. However, this is a theoretical calculation, not a clinically proven deficiency.

Practical research in sports focuses rather on gelatin or hydrolyzed collagen with vitamin C (Shaw et al., 2017) than on isolated glycine. There, an increase in collagen synthesis markers was observed, but a direct effect on injuries or tendon strength still needs confirmation.

Myths 4 and 5: 'useless' and 'safe at any dose'

Skeptics claim that glycine as a supplement is pointless altogether, because the body synthesizes it itself. Formally, glycine is indeed a non-essential amino acid. However, some researchers classify it as conditionally essential: in certain states - aging, oxidative stress, intensive tissue renewal - the need may exceed the capacity for synthesis (Wang et al., 2013).

An example is the work of the Sekhar group (2011) and Kumar (2021) on combining glycine with N-acetylcysteine in elderly people. There, the combination restored reduced glutathione levels - the main intracellular antioxidant. These are small pilot studies, but they show that the 'uselessness' of glycine is also an oversimplification.

The other extreme is the belief that glycine is safe in any quantity. In doses of up to a few grams per day it is usually well tolerated. However, in psychiatric studies where glycine was given in doses of tens of grams per day as an add-on to antipsychotics (Heresco-Levy et al., 1999), nausea and other gastric symptoms occurred. Such doses are the subject of clinical research, not self-administration.

Interactions should be considered separately. Glycine acts on NMDA receptors, so people taking psychotropic medications should discuss the supplement with a doctor. Pregnant women, children, and people with kidney or liver disease should also get a consultation before taking high doses of any amino acid.

Another common confusion is equating glycine with magnesium glycinate. In glycinate, the amino acid merely 'transports' magnesium, and its amount in a standard supplement dose is small. The effects of magnesium glycinate are related primarily to magnesium.

Editorial conclusions

Glycine is a useful amino acid, well studied from a biochemical standpoint, but most popular notions about it are either exaggerated or rest on inappropriate doses. A pharmacy 100 mg tablet is unlikely to have a noticeable pharmacological effect, while doses of around 3 g before bed have shown a moderate improvement in sleep quality in small studies.

Glycine is neither an anabolic, nor a sleeping aid, nor a completely 'empty' supplement. Its real niches - supporting sleep, collagen synthesis, and glutathione - require further independent research.

If you are considering glycine as a supplement, be guided by the doses used in studies rather than by advertising promises, and remember that a sleep routine and a full protein diet matter more.

To complete the picture, the editorial team recommends reading our materials 'What to combine glycine with,' a review of magnesium glycinate and citrate, as well as an article on supplements for sleep recovery in athletes.

References

1. Yamadera W, Inagawa K, Chiba S, et al. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5(2):126–131.
2. Bannai M, Kawai N, Ono K, et al. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012;3:61.
3. 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.
4. Meléndez-Hevia E, de Paz-Lugo P, Cornish-Bowden A, Cascante M. A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. J Biosci. 2009;34(6):853–872.
5. Wang W, Wu Z, Dai Z, et al. Glycine metabolism in animals and humans: implications for nutrition and health. Amino Acids. 2013;45(3):463–477.
6. Sekhar RV, Patel SG, Guthikonda AP, et al. Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation. Am J Clin Nutr. 2011;94(3):847–853.
7. Heresco-Levy U, Javitt DC, Ermilov M, et al. Efficacy of high-dose glycine in the treatment of enduring negative symptoms of schizophrenia. Arch Gen Psychiatry. 1999;56(1):29–36.
8. Shaw G, Lee-Barthel A, Ross ML, Wang B, Baar K. Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. Am J Clin Nutr. 2017;105(1):136–143.