Quick answer

In studies, magnesium glycinate caused few problems within the 350 mg daily limit for supplements: in a four-week trial of 250 mg a day, side effects were no more common than with placebo. Loose stools, nausea and cramping grow more likely as the dose rises, and some people should ask a doctor first.^1,2

Key facts

The adult upper limit for magnesium from supplements and medicines is 350 mg a day. Food does not count toward it.¹
Across the trials in a Cochrane review, mostly gut side effects affected 11% to 37% of people on magnesium and 10% to 14% on placebo.³
In the bisglycinate sleep trial, 93% of participants reported no side effects at all.²
The serious cases on record followed very large doses from laxatives and antacids, typically more than 5,000 mg of magnesium a day.⁴

The common side effects

High intakes of magnesium from supplements and medicines can cause diarrhea, nausea and abdominal cramping.¹

The laxative effect comes from unabsorbed magnesium salts drawing water into the intestine and colon, and from faster movement of the gut.⁴

In the trials pooled in a Cochrane review, mostly gut side effects such as diarrhea affected 11% to 37% of people taking oral magnesium, against 10% to 14% of those on placebo.³

The dose is the part you control. Magnesium the gut does not absorb is what pulls water into the bowel, and the gut takes up a smaller share of a larger dose, so one big dose, or several products taken together, makes diarrhea more likely.^4,5

Glycinate, citrate, oxide, malate and L-threonate

In the four-week trial of 250 mg of magnesium a day as bisglycinate, side effects were no more common than with placebo, and 93% of participants reported none.²

In a 12-person absorption study, glycinate was better tolerated than oxide.⁶

The forms most often reported to cause diarrhea are magnesium carbonate, chloride, gluconate and oxide.⁴

Citrate is not on NIH's list of the forms most often linked to diarrhea, but in large doses it works as a laxative: that is how the liquid sold for occasional constipation acts.^4,7

The two L-threonate trials, of 21 days and six weeks, reported it well tolerated, with fewer side effects logged than on placebo in the shorter one. Both were funded by companies that sell it. We found no trial reporting side effects of magnesium malate on its own.^8,9

Too much magnesium

The upper limit for magnesium from supplements and medicines is 350 mg a day for adults. It does not count magnesium in food and drinks.^1,4

Very large doses of magnesium from laxatives and antacids, typically more than 5,000 mg a day, have caused magnesium toxicity, including a few deaths. Signs include low blood pressure, nausea, vomiting, facial flushing, trouble passing urine and lethargy, then muscle weakness, difficulty breathing, irregular heartbeat and cardiac arrest.⁴

The risk of magnesium toxicity rises when the kidneys work poorly or have failed, because they cannot remove the excess.⁴

Some antacids and laxatives carry large amounts of magnesium: Milk of Magnesia provides 500 mg per tablespoon and Extra Strength Rolaids 55 mg per tablet, while Tums contains none.⁴

The cases NIH describes involved very large doses of laxatives and antacids, including a toddler and an older man who died. At everyday amounts, the more common way past the 350 mg limit is several magnesium products taken together, as the card below shows.^1,4

Who should ask a doctor first

People with kidney disease or reduced kidney function⁴
Anyone pregnant or breastfeeding
Anyone taking antibiotics, bisphosphonates, diuretics, long-term acid reducers, gabapentin or levothyroxine^1,10,11
Anyone already using antacids or laxatives that contain magnesium⁴

What's in ours

What’s in ours

Magnesium Glycinate: Magnesium, 275 mg per serving, from the label
Men's Multi: Magnesium, 50 mg per serving, from the label
Creatine + Electrolytes: Magnesium, 60 mg per serving, from the label

Taken together, these three come to 385 mg of magnesium a day, over the 350 mg limit for supplements. Two of them together stay under it.¹

Questions people ask

Can magnesium glycinate cause diarrhea?

It can at high doses, like any form. In the four-week trial of 250 mg a day, side effects were no more common than with placebo, and an older study found glycinate easier on the gut than oxide.^1,2,6

Can I take magnesium oxide every day?

Keep the daily total from supplements and medicines within the 350 mg adult limit. Oxide is among the forms most often linked to loose stools, and its antacid label says to take no more than two tablets in 24 hours.^1,4,12

Does magnesium interact with medicines?

Yes. NIH lists antibiotics, bisphosphonates, diuretics and long-term acid reducers, and the labels of gabapentin and levothyroxine name antacids that contain magnesium. Ask your pharmacist before combining them.^1,10,11

What are the signs of too much magnesium?

Diarrhea, nausea and abdominal cramping come first. Far larger doses can cause low blood pressure, vomiting, flushing, weakness, trouble breathing and an irregular heartbeat, which needs urgent medical care.^1,4

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See the Full Measure line Creatine + Electrolytes Magnesium Glycinate Men's Multi

Sources

This page is information, not medical advice. Talk to your doctor or pharmacist about your own situation.