Glycine for Sleep: The 3 g Dose, What It Does, and What It Does Not

Glycine before bed improved sleep quality and next-day fatigue in small human trials. The dose they used was 3 g.

It is the smallest amino acid and the main one in gelatin. I get mine from gelatin every night. Here is what the research shows and where it stops.

Does glycine help you sleep?

• Sleep-restricted volunteers. Healthy people had their sleep cut by 25% for three nights. They took 3 g of glycine or a placebo before bed. With glycine, fatigue the next day was significantly lower, sleepiness tended to be lower, and a vigilance test improved. (Bannai 2012)
• People who sleep badly. The same group reports that glycine before bedtime improved subjective sleep quality in people with insomniac tendencies. (Bannai 2012b)
• All the trials together. A 2026 scoping review found 3 trials of glycine for sleep. All 3 reported a benefit on at least one sleep outcome. (Fan 2026)

How it works

In rats, oral glycine widened the blood vessels in the skin, which lets heat out and lowers core body temperature. Falling asleep goes with a drop in core temperature. The rats fell into non-REM sleep faster. When the researchers destroyed the brain's clock region, the suprachiasmatic nucleus, the effect disappeared. (Kawai 2015)

So glycine does not knock you out. It seems to help the body do what it already does at night, which is dump heat.

Glycine dosage for sleep

The dose in the human sleep trial was 3 g before bedtime. I did not find a trial that compared different doses for sleep, so nobody knows if more is better.

Other studies used far more for other purposes: 15 g a day for 3 months in people with metabolic syndrome, and 0.8 g per kg in psychiatric trials. Those were not sleep studies.

You can also get it from food. Gelatin is about 30% glycine. (Gannon 2002) A 20 g serving of gelatin carries several grams, more than the trial dose.

Collagen has been tested directly. 13 athletic men with sleep complaints took 15 g of collagen peptides an hour before bed for 7 nights. They woke up less often, 21.3 against 29.3 times in the sleep lab. (Thomas 2024)

Glycine benefits beyond sleep

• Blood sugar. In 9 healthy people, glycine taken with 25 g of glucose cut the blood glucose response by more than 50% compared with glucose alone. (Gannon 2002)
• Oxidative stress. 60 volunteers with metabolic syndrome took 15 g of glycine a day or a placebo for 3 months. A marker of lipid peroxidation in the blood fell by 25% in the glycine group, and systolic blood pressure dropped in the men. (Díaz-Flores 2013)
• Supply. One analysis estimated that the body makes about 3 g of glycine a day, the diet adds 1.5 to 3 g, and the total may fall about 10 g a day short of what a 70 kg adult uses. (Meléndez-Hevia 2009)

My view is that glycine helps cells burn glucose, and that this is why gelatin and sugar work well together. That is my reading, not a trial result.

Glycine vs magnesium glycinate for sleep

I did not find a trial that compared the two. They are different things. Magnesium glycinate is a magnesium supplement that happens to carry some glycine.

• Magnesium bisglycinate. 155 adults with poor sleep took 250 mg of magnesium as bisglycinate, or a placebo, every day. After 4 weeks the insomnia score fell by 3.9 points against 2.3 on placebo. The authors call the effect small. (Schuster 2025)
• Magnesium in general. A meta-analysis of 3 trials in 151 older adults found people fell asleep 17.36 minutes faster on magnesium. The authors rated the evidence low to very low quality. (Mah 2021)

By my arithmetic from the molecular weights, 250 mg of magnesium as bisglycinate comes with roughly 1.5 g of glycine. That is half the dose used in the glycine trial. So a magnesium glycinate capsule is not a substitute for 3 g of glycine, and glycine is not a substitute for magnesium.

I take both.

Glycine side effects

• Very high doses over weeks. 22 patients took 0.8 g per kg a day for 6 weeks on top of their medication. It was well tolerated. (Heresco-Levy 1999)
• One very high dose. 12 healthy men took a single 0.8 g per kg dose. It impaired sensorimotor gating, a measure of how the brain filters incoming signals. (O'Neill 2011) For an adult that is around 50 g at once, far above a sleep dose.
• Serotonin, in rats. At 1 or 2 g per kg by mouth, glycine raised serotonin in the prefrontal cortex for 10 minutes. Dopamine did not change. (Bannai 2011) I treat serotonin as a stress signal, so I am telling you about it. The dose was enormous.

The abstracts of the sleep studies do not report side effects at 3 g.

The honest part

• The human sleep work comes mostly from one research group. The abstracts do not even give the number of participants.
• The main outcomes are how people felt, not hours of sleep.
• In the collagen study, total sleep time, time to fall asleep and sleep efficiency did not change. Only awakenings did.
• There is no long-term trial.

If you snore heavily, stop breathing at night or have not slept properly for months, see a doctor. Glycine will not fix sleep apnea. If you take psychiatric medication or have kidney or liver disease, ask before adding grams of any amino acid.

What I do

An hour before bed I drink warm milk with 20 to 25 g of beef gelatin and sugar. I take 300 to 500 mg of magnesium glycinate with it.

The rest matters just as much to me: a high-carb day, as much sun as possible, no phone for the last hour, and a glass of salted water.

In some posts I have also listed cyproheptadine. That is a prescription antihistamine. It is not something to take because of a blog post. Talk to a doctor.

Ray Peat described sleeping straight through the night the first time he took gelatin before bed. That account is in Ray Peat on gelatin and glycine, and his wider thinking on the subject is in Ray Peat on sleep.

More sleep research is collected in the sleep studies.

Quick answers

Does glycine help you sleep?

In small human trials, 3 g of glycine before bed improved subjective sleep quality and reduced next-day fatigue. A 2026 scoping review found 3 glycine sleep trials, and all reported a benefit on at least one outcome.

What is the glycine dosage for sleep?

The human trial used 3 g before bedtime. No trial has compared doses for sleep. A 20 g serving of gelatin contains several grams of glycine.

What are the benefits of glycine?

Besides sleep, glycine taken with glucose cut the blood glucose response by more than 50% in 9 healthy people, and 15 g a day for 3 months lowered a marker of oxidative stress by 25% in people with metabolic syndrome.

Is glycine or magnesium glycinate better for sleep?

No trial has compared them. Magnesium bisglycinate at 250 mg of magnesium a day gave a small improvement in insomnia scores in 155 adults. That amount carries roughly 1.5 g of glycine, about half the dose used in the glycine trial.

What are the side effects of glycine?

The sleep study abstracts report none at 3 g. A single dose of 0.8 g per kg impaired sensory gating in healthy men, and very large doses raised brain serotonin briefly in rats. Daily doses of 0.8 g per kg were well tolerated for 6 weeks in a patient trial.