Glycine for sleep: what the studies found, how much to take and who should avoid it

What glycine is

Glycine is the simplest amino acid. Your body makes it, and you also get it from protein foods such as meat, fish, dairy and beans. Collagen and gelatine are especially rich in it. That’s why glycine is classed as non-essential: a healthy person on a normal diet is unlikely to run short.

As a supplement, glycine comes in two main forms:

• powder in a tub, which is how it’s usually sold on iHerb;
• tablets or capsules, often with a small amount in each.

The difference goes beyond format. A tablet usually holds a small dose, while the sleep studies used 3 g at a time.

Glycine benefits: what the evidence says

People take glycine mostly for sleep, for “calm” and for memory. The evidence for each varies a lot.

How glycine might affect sleep has mostly been studied in animals. In rats it slightly lowered core body temperature and widened blood vessels in the skin. A drop in core temperature is part of the body’s normal wind-down to sleep. Whether the same mechanism works in people isn’t clear.

Glycine for sleep: the 3 g studies

Almost all the data on glycine and sleep come from a few small Japanese studies. All of them used 3 g of glycine before bed.

• People with unsatisfying sleep. Glycine improved subjective sleep quality and sleep efficiency and reduced daytime sleepiness. Sleep lab recordings (polysomnography) showed people fell asleep faster and reached deep sleep sooner, without changing the overall structure of sleep.
• Healthy men on short sleep. Time in bed was cut by about a quarter for three nights in a row. After glycine, fatigue was lower on day 1, and reaction times were better on days 1 and 3. Sleepiness didn’t change significantly.

These studies have clear limits:

• they were small: the second trial analysed just 7 people;
• some authors worked for a company that makes glycine;
• they lasted days, so there are no long-term data;
• there are no large independent trials yet.

So glycine is a cheap and, as far as we know, well-tolerated thing to try for light, restless sleep. But it isn’t a sleeping pill or a treatment for insomnia.

How to take glycine for sleep

1. Sort your routine first. Get up at the same time every day, get daylight in the morning and avoid caffeine for 6 hours before bed. Supplements do little without this.
2. Take 3 g of powder, the dose from the studies. Use the scoop that comes with the tub or kitchen scales accurate to 1 g.
3. Take it about 30 minutes before bed, stirred into a little water. Glycine tastes slightly sweet.
4. Try it for 1–2 weeks and keep a sleep diary: when you fell asleep, when you woke and how you felt in the morning.
5. Review. If nothing has changed, there’s little point continuing.

The NHS calls insomnia that lasts 3 months or longer long-term insomnia. See your GP if changing your sleep habits hasn’t helped: they may offer cognitive behavioural therapy (CBT), face to face or online. Sleeping pills are now rarely prescribed, and only for short periods. For other options, see our guide to sleep supplements and the sleep and stress section.

Glycine powder vs tablets

Check how much glycine each tablet contains. At 100 mg a tablet, you’d need 30 of them to reach the 3 g used in sleep studies, which is why powder is the practical choice.

Glycine and melatonin

There are no studies of glycine and melatonin taken together. They were studied for different problems: melatonin mainly for a shifted body clock and jet lag, glycine for light, restless sleep. In the UK, melatonin is prescription-only.

If you’re considering both:

• start with one and give it 1–2 weeks;
• add another only if the first isn’t enough;
• don’t combine either with sleeping tablets without your GP’s advice.

Glycine in magnesium glycinate

Magnesium glycinate (bisglycinate) contains glycine too, but not much. 200 mg of elemental magnesium in this form comes with about 1.2 g of glycine, less than half the dose from sleep studies. So magnesium glycinate doesn’t replace 3 g of glycine. More in our magnesium glycinate guide; for every form side by side, see types of magnesium compared. Whether you need magnesium at all is covered in magnesium deficiency symptoms.

Safety and who should avoid it

No serious side effects were reported at 3 g in the sleep studies. But they involved few people and lasted only days, so little is known about long-term use.

Check with your GP or pharmacist first if you:

• are pregnant or breastfeeding;
• want to give it to a child: doses depend on age and weight, so ask a paediatrician;
• take psychiatric medicines, sleeping tablets or anti-seizure medicines;
• have long-term kidney or liver disease.

Before you order a tub, run through this short list:

If glycine gives you nausea, an upset stomach or daytime drowsiness, lower the dose or stop.

How to choose glycine on iHerb

1. Pick a plain powder if you want to try the 3 g dose from studies.
2. Check the serving size in grams and the number of servings per tub.
3. Read the ingredients: a pure product lists glycine only, with no sugar or flavourings.
4. Compare the price per 3 g in £ or €, not per tub.
5. Skip “sleep complexes” with ten ingredients in small doses: you can’t tell what’s doing anything.

Our Supplement Facts guide explains how to read labels and work out cost per dose.