In 30 seconds
- Glycine is an amino acid that your body makes and that you also get from your diet, about 3-5 g a day.
- In the studies, 3 g before bed improved perceived sleep quality, shortened the time to deep sleep and reduced sleepiness the following day.
- With 25% fewer hours in bed, taking it 30 minutes before bed reduced tiredness the following day.
- In a 2025 trial, magnesium bound to glycine improved sleep in adults who slept poorly more than placebo did.
Glycine is a simple amino acid that, taken before bed, has been linked in studies to better sleep quality, reaching deep sleep sooner and less tiredness the following day. The amount studied is 3 g, shortly before sleep. Here is what it is, how it was taken and why it works better in good company.
What glycine is
It is the simplest amino acid, and it is not essential: your body makes it. You also get about 3-5 g a day from your diet 2.
In the nervous system it acts as a messenger in two ways. It dampens the activity of some neurons through its own receptors, and it also takes part in NMDA receptors, which are involved in activating them 3.
What the studies say
The classic studies are Japanese; the most recent one is German:
| Study | Who | How much and when | Result |
|---|---|---|---|
| Yamadera et al., 2007 | Adults who slept poorly | 3 g before bed | Better perceived sleep quality; they fell asleep sooner and reached deep sleep sooner; less daytime sleepiness |
| Bannai et al., 2012 | 7 healthy men with 25% fewer hours in bed | 3 g, 30 minutes before bed | Less tiredness on the first day and faster reactions |
| Schuster et al., 2025 | 155 adults who slept poorly | Magnesium bisglycinate, 30-60 minutes before bed, 4 weeks | Improvement on their sleep scale compared with placebo |
Sources: Yamadera et al., 2007; Bannai et al., 2012; Schuster et al., 2025.
Better sleep quality
In the Yamadera study, adults who habitually slept poorly took 3 g of glycine before bed. They rated their sleep more highly, and laboratory recordings confirmed that they fell asleep sooner and reached deep sleep sooner 1.
What is interesting is what happened the following day: they had less sleepiness and did better in memory tests. The overall structure of their sleep did not change 1.
The authors point out that the way it works is different from that of conventional sleeping medication 1.
Less tiredness after short sleep
In the Bannai study, 7 healthy men aged about 41 spent three nights with 25% fewer hours in bed: from about 7.3 to about 5.5 hours. They took glycine (3 g) or placebo 30 minutes before bed 2.
With glycine they felt less tired on the first day and reacted faster in an attention test, on the first and third days 2. It is a situation many people will recognise: weeks of heavy workload and few hours in bed.
The full data, with their level of evidence, are in glycine and sleep: what the studies say.
How it works (studies in rats)
Glycine and temperature: the route to sleep
How it works: lowering your temperature
To fall asleep, your core temperature has to drop slightly. It is one of the natural steps in the onset of sleep, and it stays low during the night 3.
In rats, oral glycine raised its level in the blood and in the fluid surrounding the brain. Afterwards, core temperature fell and blood flow to the skin increased, which is how the body releases heat 3. The authors believe this is how it helps sleep 3.
And one important detail: in rats, glycine did not change melatonin levels in the blood 2. It works by another route, through temperature.
When it was taken
Minutes before bed, in the studies
How it was taken in the studies
- Amount: 3 g 1 2.
- Timing: before bed; in one of the studies, 30 minutes before 2.
- With what: in the magnesium trial, between 30 and 60 minutes before bed 4.
- For how long: three nights in a row in the Bannai study and 4 weeks in the magnesium trial 2 4.
It is a similar window to your evening routine.
2025 trial, 155 adults
Magnesium bound to glycine: what the trial measured
Better in good company
Glycine does not have to go it alone. In magnesium bisglycinate, the mineral is bound to glycine. In a 2025 trial, 155 adults aged 18 to 65 who slept poorly took it every night for 4 weeks, between 30 and 60 minutes before bed 4.
Their sleep score improved by 3.9 points, compared with 2.3 with placebo. And 93% noticed no adverse effects 4. In an exploratory analysis, those who got the least magnesium from their diet were the ones who improved most 4. We go into it in magnesium for sleep.
That is the idea behind formulas that combine several sleep ingredients, such as glycine, magnesium, L-theanine and tryptophan.
Frequently asked questions
How much glycine do you take for sleep?
The sleep studies used 3 g, taken before bed. That is the amount with which improvements in perceived sleep quality and less tiredness the following day were seen.
When should you take glycine?
Shortly before you go to bed. In one of the studies it was taken 30 minutes before, and in a trial with magnesium and glycine, between 30 and 60 minutes before.
Does glycine make you sleepy the next day?
In the studies, the opposite: participants felt less sleepy or less tired during the day.
Can you take glycine with magnesium?
Yes. Magnesium bisglycinate combines the two, and in a 2025 trial with 155 adults who slept poorly it improved their sleep more than placebo.
Sources
- Yamadera W, Inagawa K, Chiba S, Bannai M, Takahashi M, Nakayama K. Glycine ingestion improves subjective sleep quality in human volunteers, correlating with polysomnographic changes. Sleep Biol Rhythms. 2007;5(2):126-131. View publication
- Bannai M, Kawai N, Ono K, Nakahara K, Murakami N. The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Front Neurol. 2012;3:61. View publication
- Bannai M, Kawai N. New therapeutic strategy for amino acid medicine: glycine improves the quality of sleep. J Pharmacol Sci. 2012;118(2):145-148. View publication
- Schuster J, Cycelskij I, Lopresti A, Hahn A. Magnesium bisglycinate supplementation in healthy adults reporting poor sleep: a randomized, placebo-controlled trial. Nat Sci Sleep. 2025;17:2027-2040. View publication
Information based on published studies. It does not replace the advice of a doctor or registered dietitian. The results describe what was measured in each study, not the properties of any specific product. A varied and balanced diet and a healthy lifestyle are important.
