Magnesium bisglycinate

For sleep, taken at night. A small benefit, honestly labelled.

At a glance

Our verdict	400 mg at night for poor sleep, with normal kidneys: a small benefit, low certainty. Bisglycinate only: the other forms loosen the bowels.
Best use	Sleep; a low magnesium intake
How sure the evidence is	Low for sleep
Cost a month	About $15 to $20

Written for adults in Canada. It explains the evidence; it is not advice for you personally. Last reviewed 20 October 2026.

Supplement Check

Is it right for you?

Whether magnesium suits you depends on your kidneys, your heart rhythm and the medicines you take. We check all of it, and tell you what else to stop or start. Our Supplement Check looks at:

Kidney function below normal (eGFR under 60), or unknown when there is a kidney risk
Dialysis
Myasthenia gravis
Second- or third-degree heart block, or a pulse under 50, without a pacemaker
Regular use of magnesium laxatives or antacids (milk of magnesia, magnesium citrate, Gaviscon, Maalox, Diovol)
Every medicine you take
The total across everything you already take, against the safe upper limits

Coming soon. The Supplement Check and the Online Health Assessment open once our safety testing is complete.

$59 when it opens, paid once. Adults 18 and over, anywhere in Canada. While the service is new, Dr. French reads every report himself, and your report arrives within 3 working days. More about the Supplement Check

Tell me when it opens

What it is

Magnesium is a mineral the body uses in more than 300 enzymes, in nerves, muscle and the heart. Bisglycinate is magnesium bound to the amino acid glycine (often buffered with a little magnesium oxide).

Why bisglycinate, and only bisglycinate. Dr. French's rule is to use this form alone, at night. The other common forms (citrate, oxide and others) loosen the bowels; some are sold as laxatives for exactly that reason. Bisglycinate is the gentlest on the gut at the doses used for sleep.

The product we use: a magnesium bisglycinate with 200 mg of elemental magnesium per capsule, licensed by Health Canada.

Structure of Magnesium bisglycinate — Structure: PubChem (public domain).

How it acts

Magnesium damps down excitatory nerve signalling (it blocks the NMDA receptor) and supports the brain's main calming system (GABA). It also acts like a mild calcium-channel blocker. Glycine itself may lower core body temperature as you fall asleep. These are the proposed reasons it might help sleep; they are mechanisms, not proof that it does.

Diagram: how Magnesium bisglycinate acts

Outline of a person showing where Magnesium bisglycinate acts in the body

What it is used for, and what the evidence says

Magnesium is used for a measured or likely low level (long-term acid blockers, water pills, alcohol, poor absorption), for sleep, and for migraine prevention. On this page we deal with sleep, the reason most people ask about it.

Use	What the trials found	How sure we are
Insomnia in older adults	A pooled review of 3 trials, 151 people: falling asleep 17 minutes faster (somewhere between 7 and 27 minutes); total sleep 16 minutes longer, which could have been chance. [1] The trials were small and at moderate to high risk of bias.	Low to Very low
Primary insomnia, older adults, 500 mg for 8 weeks	Better insomnia score, sleep efficiency and time to fall asleep, in a single small trial. [2]	Low
Poor sleep, adults 18 to 65, bisglycinate 250 mg for 4 weeks	155 people. The insomnia score fell 3.9 points with magnesium and 2.3 with placebo, a small difference that only just reached significance. The benefit was larger in people who ate little magnesium. [3]	Low
600 mg for sleep	No trial has tested this dose for sleep.	No evidence (no trial)

How sure we are: High means further research is very unlikely to change the answer; Moderate, it might; Low, it may well change; Very low, we are very unsure. These follow the GRADE method that guideline panels use.

Benefits

Falling asleep about 17 minutes faster (low certainty).
An insomnia score about 1.6 points better than placebo (low certainty). A change of about 6 points on that scale is usually counted as one a person notices, so this is below that line.
Cheap, and safe for most adults with normal kidneys.

Risks and side effects

Loose stools and cramps. Dose-related; this is why Canada sets the upper limit for magnesium from supplements at 350 mg a day. [4] If stools loosen, the dose is too high.
Too much magnesium in the blood (drowsiness, low blood pressure, a slow pulse, loss of reflexes, heart block). It is almost confined to people with reduced kidney function, older age, or gram doses of magnesium laxatives or antacids.

Interactions with medicines

Magnesium does not change how the liver clears medicines. Its interactions come from binding medicines in the gut, or from the kidneys.

Medicine	What can happen	What to do
Quinolone and tetracycline antibiotics, bone medicines (bisphosphonates), HIV integrase inhibitors, levothyroxine	Magnesium binds them and less is absorbed	Space the doses, or stop magnesium while taking the antibiotic
Gabapentin	About 20% less absorbed with magnesium antacids	Space by 2 hours
Spironolactone, eplerenone, amiloride, triamterene	The kidneys hold on to magnesium	Held for a doctor
Loop and thiazide water pills, acid blockers (proton-pump inhibitors)	Lower magnesium, a reason to supplement; loop-pill users often have heart or kidney disease	Loop water pills: held for a doctor
Medicines that can harm the kidneys	Raise the chance of magnesium building up	Kidney blood test first

Who should not take it

Kidney function below normal (eGFR under 60), or unknown when there is a kidney risk: a kidney blood test comes first. That includes anyone on a medicine that can harm the kidneys or with a history that could cause kidney problems.
Dialysis.
Myasthenia gravis.
Second- or third-degree heart block, or a pulse under 50, without a pacemaker.
Regular use of magnesium laxatives or antacids (milk of magnesia, magnesium citrate, Gaviscon, Maalox, Diovol).
Pregnancy and breastfeeding: food amounts are safe; no more than 350 mg from supplements, and there are no sleep trials.
Age 75 and over: no more than 350 mg without a doctor's review.
Under 18: outside the Supplement Check.

Dose and timing

400 mg of elemental magnesium (two 200 mg capsules), 1 to 2 hours before bed, with or without food.
Take it for 4 weeks with a sleep diary (time to fall asleep, waking, total sleep). If sleep does not change, stop.
600 mg only if 400 mg gives no benefit after 2 weeks, and kidney function was normal on a test in the last 12 months, and you are under 75, with no listed medicines. Dr. French is flagged on every report at this dose.
There is no dose by body weight for magnesium: trials used fixed daily doses, and safety depends on the kidneys, not on weight.
Count the magnesium in every product you take. A 50+ multivitamin plus 400 mg comes to about 450 mg.
Store at room temperature, dry.

What we know about Canadians

Magnesium is the mineral Canadians most often fall short on from food. In the 2015 national nutrition survey, 58% of men and 66% of women ate less than the average requirement, and the shortfall grows with age. [5] Among adults 19 to 64 in households with enough food it was 49%; in households with severe food insecurity it was 76%. [6] Better adherence to Canada's Food Guide (more whole grains, legumes, nuts, vegetables) cut the shortfall in people over 65 by about 20 percentage points. [7] There is no reliable blood test for body magnesium, so these intake figures are the best guide we have.

Most at risk: older adults, women, food-insecure households, diets low in whole grains, legumes and nuts, and people on water pills or long-term acid blockers.

How sure are we: moderate. National survey, but based on two days of recalled food and 11 years old.

An honest comparison: falling asleep

The same outcome, in the same units, with the cost a month in Canadian dollars.

Option	Effect	How sure we are	Cost a month (CAD)
Magnesium bisglycinate 250–500 mg	About 17 minutes faster to sleep; insomnia score 1.6 points better than placebo [1, 3]	Low to Very low	$15 to $20
Cognitive behavioural therapy for insomnia (app, programme or therapist)	19 minutes faster to sleep, 26 minutes less awake in the night; the effect lasts after treatment ends [8]	Moderate to High	Free (app) to about $90 (therapist, spread over a year)
Sleeping pill (zopiclone in Canada)	22 minutes faster to sleep on sleep studies; the benefit stops when the pill stops; falls and next-day drowsiness [9]	Moderate	$8 to $12

Our verdict

For adults with poor sleep and kidney function known to be normal: magnesium bisglycinate 400 mg at night for 4 weeks, alongside a sleep programme, which works better than either. The benefit is small and the evidence is of low certainty; this is Dr. French's judgement, and the report says so. Bisglycinate only: the other forms loosen the bowels.

Not for anyone with kidney disease, heart block, myasthenia gravis, or who already takes magnesium laxatives or antacids.

Magnesium is the mineral Canadians most often fall short on from food, it is cheap, and it is safe when the kidneys are normal. The sleep benefit is small and the trials are small, so we say so. Dr. French's rule is bisglycinate only, at night: magnesium oxide, citrate and the other forms have a laxative effect, and bisglycinate is the gentlest on the gut. Anyone taking another form is advised to switch. A kidney blood test comes first for anyone on a medicine that can harm the kidneys, with a kidney history, or with known kidney disease.