Glycine for Sleep: What the Trials Found, the Right Dose and Whether Collagen Before Bed Helps

Glycine for sleep rests on a small but interesting set of studies. Glycine is a simple amino acid your body makes and you eat every day in meat, fish, gelatin and collagen. In Japanese trials, 3 g taken before bed improved how rested people felt the next morning and shortened the time it took to fall asleep. The trials were small, short and largely run by researchers tied to an amino acid manufacturer, so treat glycine as a promising, low-cost experiment. It is not a proven treatment.

Below you will find what each key study found, the dose that was used, how glycine seems to work through body temperature, and what the collagen before bed research means for active people.

What glycine is

Glycine is the smallest amino acid. It is a building block of proteins, especially collagen, and it also works as a messenger in the nervous system. It acts on two kinds of receptors: inhibitory glycine receptors and the excitatory NMDA type glutamate receptors, where it is a co-agonist ⁴.

Your body makes glycine and you get it from food, so the studies were not correcting a deficiency. The sleep studies tested a single larger dose, taken close to bedtime, to see whether it changes sleep that night.

What the evidence says about glycine for sleep

Inagawa 2006: how you feel in the morning

The first human trial was a randomized, double-blind crossover study in volunteers who complained about their sleep quality ¹. They took 3 g of glycine or placebo before bed. The next morning, glycine improved ratings of fatigue, "liveliness and peppiness" and clear-headedness on standard questionnaires. The authors concluded that glycine produced a good subjective feeling after waking.

Yamadera 2007: sleep lab measurements

A follow-up study tested 3 g of glycine before bed in people who had been sleeping poorly over a long period, and measured sleep with polysomnography ². Glycine:

• Improved subjective sleep quality and sleep efficiency (time asleep divided by time in bed).
• Shortened the time to fall asleep and the time to reach slow wave sleep.
• Did not change overall sleep architecture.
• Reduced daytime sleepiness and improved performance on a memory recognition task.

The authors noted that glycine seemed to work differently from traditional sleeping pills such as benzodiazepines ². For background on slow wave sleep and why it matters for recovery, see REM vs deep sleep.

Bannai 2012: after short sleep

A third trial restricted volunteers' sleep to 25% less than usual for three nights in a row ³. Taking 3 g of glycine before bed significantly reduced next-day fatigue, showed a trend toward less sleepiness and improved a psychomotor vigilance test, a standard measure of reaction time and attention. In parallel rat experiments, glycine did not change melatonin levels or the expression of key clock genes, which suggests it does not shift your body clock ³.

How strong is this evidence?

Fairly weak, for three reasons:

• Small samples. These were small trials in Japan, mostly crossover designs.
• Mostly subjective outcomes. Only one study used full lab sleep recordings.
• Industry links. Several key papers come from researchers at Ajinomoto, a company that produces amino acids ³⁴⁵. That does not make the results wrong, but independent replication is limited.

There is no large meta-analysis of glycine for sleep yet. Compare that with L-theanine, where a 2025 meta-analysis pooled 19 trials (see L-theanine for sleep).

How glycine may work: body temperature

To fall asleep, your core body temperature needs to drop. Your body dumps heat through the skin of your hands and feet, which is one reason warm feet and a cool room help you drift off.

Animal research suggests glycine taps into this system. In rats, oral glycine increased glycine levels in blood and cerebrospinal fluid, increased blood flow to the skin and lowered core temperature ⁴. A later rat study traced the effect to the suprachiasmatic nucleus, the brain's master clock region ⁵. Glycine acting on NMDA receptors there increased skin blood flow and heat loss. When that brain region was removed, glycine no longer promoted sleep or lowered temperature ⁵.

Two cautions. First, this mechanism comes mostly from rats. Second, in the collagen trial in active men described below, core temperature did not differ between conditions ⁶. The temperature story is plausible and still unproven in people. You can learn more about the body clock in circadian rhythm.

Glycine dosage for sleep

All the main human sleep trials used the same glycine dosage for sleep: 3 g taken before bedtime ¹²³.

How to try it:

1. Use plain glycine powder or tablets. A small kitchen scale measures 3 g of powder more accurately than a spoon.
2. Dissolve it in water or herbal tea. It tastes mildly sweet.
3. Take it 30 to 60 minutes before bed. The papers state "before bedtime" without a precise window, so this is a practical choice.
4. Track at least one week: time to fall asleep, night wake-ups and how you feel mid-morning.
5. If you notice no benefit after two weeks, stop.

There is no evidence that more than 3 g works better for sleep. Larger doses add more chance of an upset stomach without a known benefit.

Collagen before bed: the study in active men

Collagen is rich in glycine, so researchers at Loughborough University asked whether collagen before bed could help athletes ⁶. Thirteen athletic men with sleep complaints (training about 7 hours per week) took 15 g of collagen peptides or placebo one hour before bed for seven nights in a randomized crossover trial.

Results:

• Fewer awakenings. Lab polysomnography on night 7 showed about 21 awakenings with collagen vs about 29 with placebo. Sleep diaries also showed fewer self-reported wake-ups.
• Better accuracy on a cognitive test the next morning.
• No change in total sleep time, time to fall asleep, sleep efficiency, core temperature, inflammation, hormones, sleepiness or fatigue.

This is a small trial, and two authors worked for a collagen manufacturer ⁶. Still, it is one of the few studies of a glycine-rich product in people who train. If you already use collagen for tendon or joint reasons, moving that serving to the evening is a simple test.

For people who train

Heavy training makes good sleep more important, and slow wave sleep is the deep stage most linked to physical recovery. That is the logic of supercompensation: you adapt while you rest. Glycine will not replace sleep time, but it may slightly improve sleep quality when stress, late sessions or travel disrupt it.

Practical points:

• After evening sessions: if hard evening training leaves you wired, 3 g glycine at bedtime is a low-risk trial.
• Short-sleep weeks: the sleep restriction trial suggests glycine may blunt next-day fatigue when you cannot get enough sleep ³. It does not fix the deficit.
• Collagen option: 15 g collagen peptides one hour before bed reduced awakenings in active men ⁶. It also counts toward your daily protein.
• Test early: try it in a normal training block, never for the first time in race week.
• Anti-doping: glycine is an amino acid, but supplements can be contaminated. If you are tested, choose a product with third-party certification such as Informed Sport or NSF Certified for Sport, and check the batch.

Safety

Glycine is a normal part of the diet, and the sleep trials did not report notable problems at 3 g. That said, long-term data on nightly supplementation are lacking.

• Kidney or liver disease: amino acid supplements add to the load these organs handle. Ask your doctor first.
• Psychiatric medication: glycine acts on NMDA receptors in the brain ⁴⁵. If you take antipsychotics or other psychiatric drugs, check with your prescriber.
• Pregnancy and breastfeeding: there are no safety studies on glycine supplements for sleep in this group. Get medical advice.
• Stomach upset: some people notice mild nausea or loose stools. Taking it with a little food or water helps.

Common mistakes

• Expecting sedation. Glycine does not make you drowsy like a sleeping pill. Effects are subtle.
• Mixing several supplements at once. If you start glycine and magnesium the same week, you will not know which helped. See magnesium glycinate for sleep for that option.
• Ignoring the basics. A cool room, a consistent wake time and a caffeine cutoff have stronger evidence than any supplement.

The bottom line

Glycine is cheap, familiar to the body and backed by a few small trials showing better perceived sleep and faster sleep onset at 3 g before bed ¹²³. The research base is thin and partly industry funded. For active people, collagen before bed is an interesting variation with one small positive trial ⁶. Try it for one to two weeks, measure the result and keep it only if it helps.

Frequently asked questions

How much glycine should I take for sleep?

The human sleep trials all used 3 g of glycine taken before bedtime. There is no evidence that larger doses work better for sleep, and more increases the chance of an upset stomach. Weigh the powder if you can, because a teaspoon can hold different amounts depending on the product. Take it about 30 to 60 minutes before you plan to sleep.

Does glycine make you sleepy?

Glycine does not sedate you the way sleeping pills or antihistamines do. In the trials, people fell asleep somewhat faster and felt more refreshed the next morning, and one study found less daytime sleepiness. Many people notice nothing dramatic. If you expect to feel drowsy within minutes, you will probably be disappointed, so judge it over a week or two.

Is collagen before bed as good as glycine?

Collagen is rich in glycine, and one small trial in athletic men found that 15 g of collagen peptides an hour before bed reduced night awakenings and improved a morning cognitive test. It did not change total sleep or time to fall asleep. Nobody has compared collagen and pure glycine directly, so pick the one that fits your diet and test it.

Can I take glycine with magnesium or melatonin?

Short-term combinations are common, and no clear safety problem has been reported in healthy adults. The bigger issue is that you cannot tell which product helped. Add one supplement at a time for one to two weeks. If you take prescription medication, especially psychiatric drugs, or you have kidney or liver disease, check with your doctor or pharmacist first.

Is it safe to take glycine every night?

Glycine is a normal dietary amino acid, and the short trials at 3 g did not report notable side effects. Long-term studies of nightly supplements are missing, so there is no proof either way for years of use. If you take it often, review every few weeks whether it still helps and pause it to check. Ask your doctor if you are pregnant or have a chronic illness.

Sources

1. Inagawa K et al. (2006). Subjective effects of glycine ingestion before bedtime on sleep quality. Sleep and Biological Rhythms.
2. Yamadera W et al. (2007). Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep and Biological Rhythms.
3. Bannai M et al. (2012). The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in Neurology.
4. Bannai M, Kawai N (2012). New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. Journal of Pharmacological Sciences.
5. Kawai N et al. (2015). The sleep-promoting and hypothermic effects of glycine are mediated by NMDA receptors in the suprachiasmatic nucleus. Neuropsychopharmacology.
6. Thomas C et al. (2023). Collagen peptide supplementation before bedtime reduces sleep fragmentation and improves cognitive function in physically active males with sleep complaints. European Journal of Nutrition.