Magnesium Supplement Side Effects

The most common magnesium supplement side effects are diarrhea, nausea, and abdominal cramping.

These effects are usually digestive and may be more likely with larger supplemental doses. Severe reactions are uncommon at usual doses in people with healthy kidneys, but excess magnesium can be dangerous, especially when kidney function is impaired.

Are magnesium supplements safe, and what are 3 common side effects?

Magnesium supplements are generally safe for healthy adults when used within recommended limits. Safety depends on the amount of elemental magnesium, kidney function, other medicines, and whether a clinician has recommended a higher dose.

Magnesium is an essential mineral, but taking extra is not necessary for everyone. The liver and kidneys do most of the body’s detoxification, while the lungs and gut also help eliminate waste; a supplement does not flush toxins from the body. For more on those claims, see magnesium detox.

Evidence about digestive effects is stronger than evidence comparing the tolerability of every individual product. A 2017 randomized crossover trial of magnesium chloride monitored adverse effects, but it was open-label and did not establish side-effect rates for all magnesium forms. The three effects below are recognized effects of supplemental magnesium; their likelihood can vary by dose and person.

Can magnesium supplements cause loose stools?

Diarrhea

Mechanism: Magnesium that is not absorbed can draw water into the intestine. This can make stools loose or watery, particularly when a person takes a large amount at once. Some magnesium-containing medicines use this effect deliberately as a laxative.

How to use: Check the amount of elemental magnesium on the label and avoid taking more than the recommended amount unless a clinician directs you to do so. If the label permits, taking the supplement with food or dividing the daily amount between meals may help some people tolerate it. If diarrhea begins after an over-the-counter supplement, stop taking it and ask a clinician or pharmacist for advice; do not change a prescribed medicine without contacting its prescriber.

Evidence: Diarrhea is a well-recognized effect of excess supplemental magnesium. Available evidence does not establish a dependable side-effect ranking for every magnesium form, so a product marketed as gentle can still cause diarrhea.

Persistent or substantial diarrhea can lead to dehydration. Seek medical advice if it continues, is severe, or makes it difficult to drink enough fluids.

Can magnesium supplements make you feel sick?

Nausea

Mechanism: Magnesium supplements can upset the digestive tract, causing a queasy feeling or, sometimes, vomiting. A large dose may be harder to tolerate, although nausea has many possible causes and does not prove that magnesium is responsible.

How to use: If the product instructions allow it, take the supplement with a meal rather than on an empty stomach. Review the serving size: a full serving may contain more than one pill, and taking extra pills increases the amount of magnesium consumed.

If nausea starts after an over-the-counter supplement, stop taking it and speak with a clinician or pharmacist, particularly if the symptom does not go away. Ask the prescriber before changing a prescribed magnesium product.

Evidence: Nausea is a recognized adverse effect of magnesium supplements, particularly at excessive intakes. The available study evidence is limited for predicting which person will experience it or which product will prevent it.

Can magnesium supplements cause stomach cramps?

Abdominal cramping

Mechanism: Unabsorbed magnesium changes how much water is present in the bowel and can be accompanied by abdominal discomfort or cramping. Cramps may occur along with loose stools, but they can also have causes unrelated to a supplement.

How to use: Check whether you are taking more than the label recommends or getting magnesium from multiple products. If an over-the-counter magnesium supplement appears to cause cramping, stop it and ask a clinician or pharmacist whether you need the supplement and what amount is appropriate.

Taking a smaller amount with food may be easier to tolerate for some people, but ask about the right amount before restarting if symptoms were troublesome. Do not increase the dose to try to overcome digestive symptoms.

Evidence: Abdominal cramping is a recognized effect of excessive supplemental magnesium. There is limited evidence for reliably predicting cramps from a particular form or dose in an individual. Severe, worsening, or persistent abdominal pain needs medical assessment rather than an assumption that the supplement is the cause.

Who should avoid magnesium supplements or get advice first?

People with kidney disease, especially advanced kidney disease or kidney failure, should not start an over-the-counter magnesium supplement without medical advice. The kidneys normally remove excess magnesium; when they cannot do so effectively, magnesium can build up in the blood. This can happen with magnesium-containing laxatives or antacids as well as supplements.

Ask a clinician or pharmacist before using magnesium if you take medicines regularly. Magnesium can interfere with the absorption of certain antibiotics and osteoporosis medicines, while some other medicines can affect magnesium levels. A clinician or pharmacist can advise whether doses need to be separated and whether a supplement is appropriate; do not stop or change prescribed medicines on your own.

People who are pregnant or breastfeeding should discuss any supplement with their prenatal or other healthcare professional. Ask a child’s healthcare professional before giving a child magnesium supplements: adult limits and adult product directions do not automatically apply to children.

Avoid a product if you have had an allergic reaction to it or one of its ingredients. Seek emergency help for symptoms of a serious allergic reaction, such as trouble breathing or swelling of the lips, tongue, or throat.

What is the safe daily amount of magnesium?

For adults, the upper limit is 350 mg of elemental magnesium per day from supplements and medicines, unless a healthcare professional directs otherwise. This limit includes magnesium in products such as laxatives and antacids; it does not include magnesium naturally present in food. It also applies during pregnancy and breastfeeding.

The upper limit is not a recommendation that everyone take 350 mg per day. It is a ceiling for unsupervised supplemental intake, not a target or a measure of how much magnesium your body needs from all sources. A clinician may recommend a higher amount for a specific reason and monitor its use.

Read the supplement facts panel for the amount of magnesium per serving. That amount refers to elemental magnesium, rather than the total weight of the magnesium compound. Check how many tablets, capsules, or scoops make up one serving, and add magnesium from other supplements and medicines when assessing your total.

Children have different limits depending on age. For a child, ask a healthcare professional about the appropriate product and amount rather than using the adult limit.

When should you see a doctor?

Contact a healthcare professional if diarrhea, nausea, or cramps are persistent, recur when you take magnesium, or interfere with eating and drinking. Seek prompt medical advice for severe abdominal pain, blood in the stool, repeated vomiting, or signs of dehydration such as dizziness or very little urine.

Too much magnesium can cause more serious symptoms, especially in someone with impaired kidney function. Get emergency help for trouble breathing, fainting, severe weakness, confusion, or a new irregular heartbeat. These symptoms need urgent assessment regardless of whether magnesium is the cause.

If you suspect a large overdose, contact a poison control service promptly rather than waiting for symptoms. Tell the service or healthcare professional which product was taken, its strength, approximately how much was taken, and when. Bring the packaging or a photo of the label if you need medical care.