Glycine
The smallest amino acid, best known as something people take before bed.
- Sleep and winding down
- Antioxidants and glutathione
A plain-English overview, not advice. Written from published reviews and trials and from what people say in public forums.
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On this page
What is glycine?
Glycine is the smallest of the amino acids that build the body’s proteins: where the others carry a long side chain, glycine carries a single hydrogen atom. The body makes its own, mainly in the liver and kidney and mostly out of other amino acids, and more arrives in food, which is why it has long been called non-essential, though several reviews now argue that what the body makes, plus what food brings, falls short of what it spends, and call it conditionally essential instead. Together with two related amino acids it accounts for more than half of the amino acids in collagen, the protein that gives skin, bone, cartilage and blood vessel walls their structure. On a UK shelf it is plain glycine, as powder or capsules, with no competing chemical forms to weigh up.
Why do people take glycine?
Sleep and winding down
The thinking. Sleep is what most people buying glycine are after, usually a few grams in water in the last hour before bed. Reviews describe two routes for the idea: glycine is a signalling chemical in its own right in the nervous system, and it appears to nudge body temperature down, the same drop that normally comes with falling asleep.
What research has found. A 2026 review that gathered this literature found that all three trials of glycine and sleep reported a difference on at least one sleep measure, though most of the work it collected was about how much glycine reaches the blood. In a crossover study, 3 g before bed in volunteers whose sleep had been cut by a quarter left next-day fatigue scores and a reaction-time test ahead of placebo, while sleepiness itself only trended that way. A 2024 review that ranged across eleven body systems reported better sleep in healthy adults, while saying plainly that those studies were small and at high risk of bias. Research here is still young: a few studies so far, mostly pointing the same way.
Antioxidants and glutathione
The thinking. The body’s main in-house antioxidant is glutathione, and glycine is one of the three amino acids it is assembled from. Reviews make the case that glycine is the one in shortest supply, so how much is around sets the pace at which glutathione can be made. That is the thinking behind taking it with everyday wear and ageing in mind.
What research has found. One trial has measured this directly. Sixty adults with metabolic syndrome, the cluster of blood pressure, blood sugar and waist measurements that tend to travel together, took 15 g a day or a placebo for three months; the glycine group ended with a quarter less of a blood marker of fat damage, alongside shifts in two of the enzymes that handle oxidation. The same trial recorded a fall in systolic blood pressure among the men taking part. Few studies have measured this yet, so there is little to go on either way.
What does glycine do in the body?
Glycine is both a building block and a supply line. Most of it is built into proteins, collagen above all, but a steady share is spent making other things the body runs on: glutathione, its main in-house antioxidant; creatine; haem, the part of red blood cells that carries oxygen; and the purines that go into DNA. What the body makes for itself, plus what a normal diet brings, comes to less than all that spending needs, by the reckoning of several reviews.
It is also a signalling molecule, which is the side the sleep research leans on. Glycine fits receptors and transporters found on many kinds of cell: in the nervous system it opens channels of its own and acts as a partner at another receptor, and elsewhere reviews describe it quietening the switch that turns inflammatory genes on. Blood glycine tends to sit low in people carrying extra weight or living with type 2 diabetes, and rises again with exercise or weight-loss surgery.
What do people say about taking glycine?
These are anecdotes people have shared, not evidence.
What people like
- They come from three threads in one community of people with long-term fatigue, so a strong reaction may reflect the group as much as glycine.
- Several describe falling asleep more easily or waking less often, usually noticed within the first few weeks of taking it at night.
- Two describe staying on it for a year or more without trouble, one of them at a few grams a night.
Common complaints
- Two describe feeling wiped out and foggy the day after starting: one stopped within days, the other built up slowly from a small amount.
- A couple tried it and noticed little or nothing for their sleep, and moved on to something else.
How people take it
- Three grams at night is the amount most of those giving a figure describe, with one taking more than five.
- Two split it, taking some at bedtime and more on waking in the night, rather than one larger amount.
- Two pair it at bedtime with something else, naming niacin, theanine, lysine or GABA rather than taking it alone.
- A couple take it spread through the day rather than at bedtime.
Read from these public discussions:
- Glycine for REM Sleep? (Phoenix Rising forums, 2018)
- Insomnia ideas? (Phoenix Rising forums, 2017)
- Glycine: cause weight gain? increase norepinephrine? (Phoenix Rising forums, 2015)
What forms of glycine are there?
| Form | What’s different | Per serving, on products we list |
|---|---|---|
| Glycine | Plain glycine, the amino acid itself, with no other chemical form of it on the shelf. | 2 g |
What else is worth knowing about glycine?
- Trials have used very different amounts: 3 g before bed in the sleep crossover, and 15 g a day for three months in the oxidative stress trial. Labels give glycine per serving, and a serving is often more than one capsule or scoop, so the figure on the front is not always what one capsule holds.
- People often pick glycine up as a building block for collagen, with skin or joints in mind. That rests on what the body does with glycine, which is one of the amino acids collagen is built from, rather than on trials of people taking it: the collagen work behind this page is chemistry and animal research.
- Who took part matters. The oxidative stress trial was in 60 adults with metabolic syndrome, and the sleep crossover was in healthy volunteers whose sleep had been deliberately cut by a quarter for three nights, rather than in people with long-standing sleeplessness.
- The studies behind this page do not report on side effects either way, so there is nothing to pass on about how the amounts they used were tolerated.
If you take medication, are pregnant, or have a health condition, check with a pharmacist or GP first.
The research behind this page (10 studies)
- The effect of glycine administration on the characteristics of physiological systems in human adults: A systematic review. (2024, systematic review)
- Glycine Bioavailability and Sleep-Related Outcomes Following Oral Glycine and Collagen Supplementation-A Scoping Review. (2026, other)
- The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. (2012, other)
- Oral supplementation with glycine reduces oxidative stress in patients with metabolic syndrome, improving their systolic blood pressure. (2013, randomised trial)
- Roles of dietary glycine, proline, and hydroxyproline in collagen synthesis and animal growth. (2018, review)
- Glycine Metabolism and Its Alterations in Obesity and Metabolic Diseases. (2019, review)
- Glycine: The Smallest Anti-Inflammatory Micronutrient. (2023, review)
- Multifarious Beneficial Effect of Nonessential Amino Acid, Glycine: A Review. (2017, review)
- Dietary Glycine Is Rate-Limiting for Glutathione Synthesis and May Have Broad Potential for Health Protection. (2018, review)
- Impaired "Glycine"-mia in Type 2 Diabetes and Potential Mechanisms Contributing to Glucose Homeostasis. (2017, review)
How much does glycine cost?
That depends on the form and the pack, so we work out the price of the same dose of every glycine product we can find and rank them.