Glycine
Popular bedtime amino acid.
SLEEP • LONG-TAIL
Glycine before bed (UK): benefits and how to use it
How glycine is used for sleep and what to expect.
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Quick answer
How glycine is used for sleep and what to expect.
- Glycine works partly by lowering core body temperature, which is one of the physiological triggers for sleep onset.
- The studied dose is 3g taken about an hour before bed.
- The trials are small and mostly measure subjective sleep quality and next-day alertness rather than sleep architecture.
- It is cheap, well tolerated, and one of the few sleep supplements with a plausible mechanism rather than just marketing.
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Important: This content is informational only and not medical advice. Read full disclaimer.
On this page
How glycine actually works
Glycine is a non-essential amino acid that also acts as an inhibitory neurotransmitter. The mechanism that makes it interesting for sleep is thermoregulatory: glycine promotes peripheral vasodilation, which increases heat loss through the hands and feet and lowers core body temperature.
That matters because a falling core temperature is one of the physiological signals for sleep onset. It is the same reason a warm bath 90 minutes before bed helps — the bath itself does not cool you, but the vasodilation afterwards does.
Whether that translates into meaningfully better sleep is a separate question, and the honest answer is that the effect is modest.
What the evidence shows
| Finding | Strength | Note |
|---|---|---|
| Improved subjective sleep quality | Small trials, consistent direction | Participants reported better sleep, not necessarily measurably deeper sleep |
| Faster sleep onset | Some support | Consistent with the temperature mechanism |
| Better next-day alertness and reduced fatigue after restricted sleep | Some support | One of the more interesting findings — it helped most in sleep-restricted participants |
| Changes in sleep architecture | Limited | Not a slow-wave sleep agent despite being marketed that way |
| Long-term outcomes | Not studied | Trials are short |
The overall picture: a plausible mechanism, small positive trials, modest effect size, good safety. That is better than most sleep supplements manage and it is not a treatment for insomnia.
Dose and timing
Below studied range
1 g
Studied sleep dose
3 g
Upper end used in trials
5 g
Take it about 60 minutes before bed. Glycine is naturally sweet and dissolves easily in water, which is why the powder is usually better value than capsules — 3g is six or seven 500mg capsules but a single small scoop of powder.
It is generally well tolerated. Mild nausea or loose stools are the most commonly reported effects, usually at higher doses. It is also found in collagen supplements and bone broth, so you may already be getting some.
Who it suits, and who it does not
Reasonable to try if you take a long time to fall asleep, run warm at night, feel unrefreshed after adequate hours, or are in a period of restricted sleep and want to reduce the next-day cost.
Not the answer if you snore loudly, wake gasping, wake repeatedly to pee, drink most evenings, or have had insomnia for months. Each of those has a specific cause that glycine does not touch — see apnoea signs, nocturia and alcohol and sleep.
Compared with the alternatives: L-theanine suits a mind that will not switch off, magnesium glycinate suits physical tension, and glycine suits running warm and slow onset. They address different problems.
General information for UK adults, not medical advice. Speak to your GP or pharmacist before starting a supplement if you take medication or have a health condition.
When to speak to a GP
Do not cover these with a supplement. Loud snoring, witnessed breathing pauses, waking gasping or choking, morning headaches, or falling asleep during the day point at obstructive sleep apnoea, which is common in men over 40 and treatable. Start with the apnoea risk checklist and the signs, then speak to a GP. Insomnia lasting more than three months also warrants a GP conversation — CBT-I, not a supplement, is the recommended first-line treatment in the UK.
FAQ
How much glycine should you take before bed?
The studied dose is 3g taken about an hour before bed. Trials have used up to 5g. Powder is usually better value than capsules, since 3g is six or seven 500mg capsules but one small scoop.
How does glycine help sleep?
Mainly through temperature. Glycine promotes peripheral vasodilation, increasing heat loss through the hands and feet and lowering core body temperature — and a falling core temperature is one of the physiological triggers for sleep onset.
Does glycine actually work for sleep?
The trials are small but consistent in direction: better subjective sleep quality, faster onset, and improved next-day alertness after restricted sleep. The effect is modest, and it is not a treatment for insomnia.
Is glycine safe to take every night?
It is generally well tolerated at 3g. Mild nausea or loose stools are the most commonly reported effects, usually at higher doses. Long-term use has not been studied, and you should check with a pharmacist if you take medication.
Should you take glycine or magnesium for sleep?
They suit different problems. Glycine fits slow sleep onset and running warm at night; magnesium glycinate fits physical tension and restlessness. L-theanine fits a mind that will not switch off.