Magnesium glycinate and sleep: what the research actually shows

Magnesium glycinate (also called bis-glycinate) is magnesium bound to two molecules of the amino acid glycine. The form is popular online because it's better absorbed than magnesium oxide and less likely to cause loose stools than magnesium citrate at equivalent doses.

The research base#

Most published human trials of magnesium for sleep use magnesium oxide or magnesium citrate, not glycinate, and most are in older adults or specific patient populations. The headline numbers most often cited are:

A small RCT in older adults (Abbasi et al., 2012) reported improved subjective sleep parameters with 500 mg/day of magnesium oxide for 8 weeks.
A 2021 systematic review (Mah & Pitre) of three small RCTs concluded the evidence was low-quality and the population was older adults with insomnia, not general adults.

There is almost no direct human RCT evidence on magnesium glycinate specifically for sleep at the time of this review. Most claims about glycinate's effect on sleep are extrapolated from (a) magnesium oxide trials and (b) the mechanistic action of glycine itself.

The glycine angle#

Separately from magnesium, glycine as a standalone amino acid (typically 3 g taken 30–60 minutes before bed) has small RCTs showing subjective improvements in sleep quality and reduced daytime sleepiness (Yamadera et al., 2007; Bannai et al., 2012). Whether the glycine in magnesium glycinate is enough to reproduce that effect is unclear; a 200 mg elemental magnesium dose typically contains less than 2 g of glycine.

What we'd actually say#

The case for magnesium glycinate for sleep is mostly:

Magnesium deficiency is plausibly common in modern diets (NHS RDA in the UK is 300 mg/day for men, 270 mg/day for women).
Glycinate is well-tolerated and well-absorbed.
The downside is small at typical doses.
The direct sleep evidence is C-grade: plausible mechanism, weak human trials, not in the population most readers are in.

Practical considerations#

The MHRA does not regulate magnesium supplements as medicines, but high doses (>400 mg elemental, from supplements) can cause diarrhoea.
If you take medications, check interactions. Magnesium can reduce absorption of some antibiotics (tetracyclines, quinolones) and thyroid medication.
For people with kidney disease, supplemental magnesium can accumulate. Talk to your GP.

This isn't dosing advice. It's a summary of what the evidence currently supports, and crucially, where it doesn't.

When to talk to a clinician

Educational content has limits. The following are reasons to talk to a UK-registered GP, contact NHS 111, or in an emergency call 999.

Chronic kidney disease — supplemental magnesium can accumulate

On warfarin, tetracyclines, quinolones, or thyroid medication (interaction or timing issues)

Persistent insomnia — supplements are not a substitute for proper assessment

Frequently asked

Should I take magnesium glycinate or citrate for sleep?

If you want both supplementation and a mild laxative effect, citrate. If you want GI tolerance at higher doses, glycinate. There's no clean head-to-head trial showing one outperforms the other for sleep specifically.

How much should I take?

Trial doses for sleep-related magnesium research are usually 200–500 mg elemental magnesium per day. Above 400 mg from supplements is where loose stools become common. We don't give personal dosing advice — discuss with a pharmacist or GP.