Does Magnesium Citrate Upset Your Stomach? Dose Is the Key

Magnesium citrate has a reputation as a laxative, but that reputation comes from large amounts sold for constipation and bowel prep.

Magnesium citrate dissolves easily in water, and magnesium that stays in the gut pulls water into the stool. MedlinePlus^[3] describes it as a saline laxative, meaning a salt that makes the stool hold water. That softens the stool and increases bowel movements.

The same MedlinePlus page lists loose, watery or more frequent stools as the common side effect of the laxative product. A bowel movement usually comes within 30 minutes to 6 hours.

So the effect is real, but it is the purpose of the laxative product. The question for a daily supplement is how much magnesium reaches that point, and that depends on the amount.

A laxative is meant to produce watery stools within hours, while a daily supplement is meant to add to your regular magnesium intake. The two products differ in purpose, in amount and in how long they are used.

MedlinePlus says the laxative form should not be used for more than 1 week unless a doctor directs it. It also tells users to mix the powder with 10 oz (296 mL) of cold water or take the liquid with a full glass of liquid.

Magnesium also does a regular job in the body: it is involved in hundreds of processes, including muscle and nerve function.* A supplement serves that role, and a laxative does not.

The adult upper limit for magnesium from supplements is 350 mg a day, and diarrhea is the effect that limit was built around. We come back to it below.

For reference, our magnesium citrate† has 325 mg of magnesium per scoop. † The pouch holds magnesium carbonate; in water it turns into magnesium citrate.

Most trials at moderate amounts found no significant extra diarrhea compared with placebo. A 2023 review in Advances in Nutrition^[1] looked at studies from 1997 to 2022 that tracked diarrhea on purpose.

What was reviewed: 10 studies, 5 meta-analyses and 5 randomized trials.

What changed: Seven of them, with magnesium intakes from 128 to 1,200 mg a day, found no significant difference in diarrhea between magnesium and control groups.

Reports to the FDA: a search of its adverse event database found 40 stomach-related cases tied to single-ingredient magnesium products, and about a third mentioned diarrhea.

The catch: the review is a perspective paper by authors who argue the upper limit should be raised, and it is not a new trial. Other analyses it cites found diarrhea in 11% to 37% of people taking magnesium, against 10% to 14% on placebo.

A 24-week trial of three forms

Who took part: 164 adults, mean age 63, given magnesium citrate, oxide, sulfate or placebo.

Daily dose: 450 mg of magnesium, split into three times a day.

What changed: on stomach symptom scores, citrate did not differ from placebo. Sulfate scored higher for stomach complaints at 24 weeks.

The catch: mild diarrhea was reported by 13 people across the whole trial, and 2 people on citrate stopped because of stomach complaints. The trial was about blood vessel stiffness, not stomach comfort.

Some evidence says yes. The 2023 review notes that magnesium supplements are best taken with food and that large doses are spread across the day, as the review^[1] puts it.

One older trial it describes used 476 mg of magnesium oxide a day for 60 days. Diarrhea occurred in 18 of 50 people, and some symptoms eased when the magnesium was taken with food.

Splitting is how the 24-week trial above delivered 450 mg a day, in three parts rather than one. Smaller amounts at a time mean less unabsorbed magnesium reaching the lower gut at once.

Water: magnesium citrate powders and the laxative are both mixed into a glass of liquid. The MedlinePlus laxative page lists 10 oz of cold water for the powder form.

The form also matters. The review says citrate is highly water-soluble and oxide poorly soluble, and that effervescent forms dissolve better than single-dose tablets. See our guide to how the magnesium forms differ.

The adult upper limit is 350 mg a day, and it covers magnesium from supplements and medications only. Magnesium from food does not count toward it.

The U.S. Institute of Medicine set that number in 1997. The 2023 review^[1] explains that the committee used 360 mg a day as the lowest level where an effect appeared, with diarrhea as the effect. It described a mild, reversible effect that some people get at amounts others tolerate easily.

That is why the limit is a stomach limit. It was drawn at the point where loose stools started to show up in some people, not at a point of serious harm.

The takeaway: stomach effects follow the amount at one time, the form and whether it is taken with a meal. A daily citrate serving that stays under 350 mg, spread through a day, sits in the range where most trials saw no significant extra diarrhea. A laxative product sits in a different category by design.

People with kidney problems need the most care, because healthy kidneys clear extra magnesium and reduced kidney function makes that harder. MedlinePlus^[4] says side effects from high intake are mainly a concern for people with significantly reduced kidney function.

The laxative product's page also asks users to tell a doctor about pregnancy, breastfeeding and medicines, and to separate other medications from magnesium citrate by at least 2 hours before or after. That wording is for the laxative, and it shows why medicine timing is a question for a pharmacist.

Check with your doctor first if you:

• Have kidney disease or reduced kidney function
• Are pregnant, planning pregnancy or breastfeeding
• Are giving magnesium to a child, since limits are lower and a pediatrician should decide
• Take prescription or nonprescription medications
• Have stomach pain, nausea or vomiting, or a sudden change in bowel habits

The NIH upper limit for adults is 350 mg a day from supplements and medications combined. Bloody stools, or no bowel movement after a magnesium laxative, are reasons to stop and call a doctor right away.