Glycine Simply Explained

1. What Is Glycine?

Glycine is the smallest amino acid (protein building block) and occurs in almost all proteins. The body can produce glycine itself. Through the diet, we take it in with protein. It is also used as an additive in foods, as an excipient in medicines, and as a dietary supplement.

2. Where Is It Found, and What Is It Made From?

Glycine is found in almost all proteins, especially abundantly in collagen and gelatin. In the body, it is present in blood and tissue and serves as a messenger substance in the nervous system. For studies and preparations, glycine is usually produced chemically or obtained from proteins and processed into powder, capsules, or solutions.

3. What Does Glycine Do? What Research Shows

Psychiatry and Nervous System

For psychotic symptoms, two reviews report benefits from glycine 45. However, the studies were mostly small and short. As an add-on to clozapine (a medication), glycine showed no benefit in a small controlled study (with a comparison group) 17. Whether glycine reliably helps in larger studies is still unclear.

Sleep and Falling Asleep

A review reports better sleep in healthy people with longer glycine intake; however, the studies on this were small and their results easily biased 4. Another review found at least one improved sleep measure in all three sleep studies with glycine 2. Whether the sleep effect is confirmed in larger placebo-controlled (sham substance) studies remains open.

Wound Healing

In patients with early dental implant inflammation, plaque, bleeding tendency, and two inflammatory messenger substances decreased after cleaning with glycine powder jet 7. After six months, an inflammation value was higher with glycine than with erythritol powder 7. Here only a single study counts, and glycine was used as a blasting powder, not swallowed. Therefore, the informative value is weak. Controlled studies with ingested glycine for wound healing are still pending.

Metabolism and Blood Sugar

A controlled study in dialysis patients found no difference between glycine and branched-chain amino acids in gut hormones 10. A mixture of glycine and N-acetylcysteine improved cellular fat burning and insulin resistance in older adults compared with a sham substance; what share glycine has in this is open 13. In people with severe obesity (adiposity), triglycerides (blood lipids) decreased with glycine without a comparison group, while weight remained the same 19. Whether pure glycine alone improves blood sugar or metabolism is open.

Liver and Fatty Liver

For liver and fatty liver, there are no controlled studies on glycine alone; the evidence is unclear. A small study with 19 participants with severe obesity found improvements in liver values with ingested glycine without a comparison group 19. A review mentions a possible benefit of glycine flushing solution in liver transplants, mainly based on animal and cell findings 24. The effect and safety of pure, ingested glycine in humans are open.

Blood Flow and Tissue Damage

A large genetic analysis found an association between higher blood glycine levels and less coronary heart disease (narrowing of the coronary arteries) 1. In ventilated COVID-19 patients, glycine via the tube lowered fibrinogen levels (a protein involved in blood clotting), but not mortality or ventilation duration 12. Controlled studies with pure glycine on the heart and blood vessels are still pending.

Other Investigations

The controlled studies in this area predominantly show no advantage of glycine. In people with alcohol dependence, glycine compared with placebo changed neither craving nor drinking amount in the laboratory 8. In ventilated intensive care patients, glycine levels in blood and muscle increased, muscle wasting did not differ with certainty 9. In malnourished dialysis patients, the fat-free mass index turned out more favorable with glycine than with branched-chain amino acids 11. The evidence is weak because the studies are small and investigate different forms. Mixtures such as glycine plus N-acetylcysteine do not allow conclusions about glycine alone 613.

4. How Was Glycine Taken in the Studies?

Some studies tested mixtures, for example glycine together with N-acetylcysteine (GlyNAC) or with carnitine and a low-protein diet. These forms cannot be directly compared with one another; the doses are shown in the table.

5. Is Glycine Safe? Side Effects in the Studies

In a study with children who had sleep problems, a side effect occurred with glycine, but it was not serious; both treatments were well tolerated 14. A case report describes confusion, seizures, and a too-low sodium level in the blood after a hysteroscopy with glycine flushing fluid, which resolved after treatment 20. In people with schizophrenia who took the medication clozapine, delusional symptoms decreased only without glycine; the researchers suspect that glycine could interfere with the effect of the medication 17.

All details with tables and sources: full expert page on Glycine