Magnesium is a mineral involved in muscle and nerve function, bone health, and blood pressure control.

Your healthcare provider may recommend a magnesium supplement if you have heart disease, osteoporosis, migraines, or constipation.

Taking too much magnesium can increase your risk of side effects like diarrhea, nausea, vomiting, and stomach pain.

Gastrointestinal (GI) side effects are most commonly reported with magnesium supplements. These side effects are more likely to occur with magnesium doses over 350 milligrams.

Very high doses of magnesium can lead to magnesium toxicity, which can cause several serious and dangerous side effects.

Gastrointestinal Symptoms

Gastrointestinal symptoms are the most commonly reported side effects with magnesium use. These include diarrhea, nausea, vomiting, stomach pain, and stomach cramping.

Magnesium supplements are commonly taken to treat constipation. The supplement helps by bringing water into your intestines, softening your stool (poop) and making it easier to have a bowel movement. The effect magnesium has on the intestines is what leads to GI side effects.

Magnesium forms commonly reported to cause diarrhea include magnesium carbonate, chloride, oxide, and gluconate. The chance of gastrointestinal side effects increases with magnesium doses larger than 350 milligrams.

If you are experiencing symptoms like nausea, diarrhea, and stomach pain while taking magnesium, taking the supplement with food may help.

Magnesium Toxicity

Very high doses of magnesium (more than 5,000 milligrams per day) can lead to magnesium toxicity, where magnesium levels in the blood reach 1.74-2.61 millimoles per liter. A normal blood magnesium level is usually 0.75-0.95 millimoles per liter.

Symptoms that may develop with magnesium toxicity can include:

• Hypotension (low blood pressure)
• Facial redness and flushing
• Confusion
• Difficulty urinating
• Tiredness or fatigue
• Muscle weakness
• Difficulty breathing
• Slow, fast, or abnormal heartbeat
• Heart failure
• Coma
• Cardiac arrest (when the heart stops beating)

Magnesium toxicity is rare, and these symptoms are more likely to occur when magnesium is given intravenously (through a vein). However, very high doses of magnesium supplements can cause magnesium toxicity. Your risk is increased if your body cannot properly remove magnesium through the kidneys.

The risk of side effects is higher if you have a history of kidney failure or impaired kidney function. This includes people who receive dialysis or have chronic kidney disease (CKD). Kidney function also decreases as you get older.

Your kidneys help remove extra magnesium from your body through urine. If your kidneys don’t work properly, magnesium can build up and cause unwanted side effects.

Certain forms of magnesium, such as magnesium oxide or sulfate, may also be more likely to cause side effects.

The daily limit for supplemental magnesium is 350 milligrams for adults. This limit does not include magnesium from foods like green leafy vegetables and nuts. You should not consume more magnesium than this limit unless recommended by your healthcare provider.

The daily recommended value for magnesium, from food and supplement sources, depends on your age and sex:

• Men: 410 milligrams if you’re 14-18 years old, 400 milligrams if you’re 19-30 years old, and 420 milligrams if you’re 31 years and older
• Women: 360 milligrams if you’re 14-18 years old, 310 milligrams if you’re 19-30 years old, and 320 milligrams if you’re 31 years and older
• People who are pregnant: 400 milligrams if you’re 14-18 years old, 350 milligrams if you’re 19-30 years old, and 360 milligrams if you’re 31 years and older
• People who are breastfeeding: 360 milligrams if you’re 14-18 years old, 310 milligrams if you’re 19-30 years old, and 320 milligrams if you’re 31 years and older

Read the supplement label and talk with your healthcare provider to determine the best dose for your specific health needs.

If you’re taking magnesium and experience any pain or symptoms associated with magnesium toxicity, stop taking the supplement and speak with a healthcare provider.

If you see blood in your stool or notice black, tarry stools after taking magnesium, stop taking the supplement and talk to your healthcare provider immediately. This may be a sign of bleeding in your GI tract.

Before taking a magnesium supplement, speak with your healthcare provider. They can help you determine if the supplement is safe for you and how useful it may be in treating your condition.

Magnesium plays an important role in many body processes, including muscle and nerve function, bone health, and blood pressure control.

Taking too much magnesium can increase your risk of side effects. Very high doses of magnesium can cause serious side effects like low blood pressure, muscle weakness, and coma.

Before taking a magnesium supplement, talk to your healthcare provider. They can help you decide if the supplement is useful and safe for you to take.