Magnesium is a vital mineral that your body needs. It regulates certain biochemical functions in the body, including protein synthesis, blood sugar control and blood pressure regulation. It’s also needed for energy production and the synthesis of DNA and RNA, is important for the structural development of bones and plays a role in transporting calcium and potassium for muscle, heart and nerve function. Needless to say, your body relies on magnesium in a lot of ways.

However, some people may not be getting enough magnesium from their diets, which is why doctors may recommend a supplement, especially to address certain problems, like constipation, sleep problems and muscle cramps, says Laura Purdy, M.D., a board-certified family medicine physician and the medical director at Swell Medical.

But as useful as a supplement may be, is there such a thing as taking too much magnesium? We consulted the latest research and spoke with medical experts on what happens to your body if you take too much magnesium, including the warning signs to look out for.

How Much Magnesium Is Safe?

The current Recommended Dietary Allowance (RDA) of magnesium for adults is:

• Ages 19 to 30: 400 milligrams (mg) (males) and 310 mg (females)
• Ages 31 and over: 420 mg (males) and 320 milligrams (females) 

Magnesium is naturally present in many foods, such as almonds, spinach, kidney beans and tofu. If you’re not getting enough of it, some doctors might recommend taking a supplement. “It’s important to connect with your doctor to discuss your current diet and a proper dose for your body specifically,” says Purdy. “The recommended dose will range depending on the supplement and the brand. It’s important to follow the label instructions and consult with your doctor, taking your current diet and needs into consideration. It is also recommended to take the supplement with food when possible,” she explains.

What is Magnesium Overdose?

Magnesium overdose—also known as hypermagnesemia is highly unlikely. The tolerable upper intake levels of magnesium is 350 mg, the amount unlikely to cause side effects. Eating too much magnesium from food is not harmful. However, high doses of magnesium via dietary supplements, such as magnesium oxide, citrate or chloride, can cause trouble. “This is, generally speaking, fairly rare, but if you take too much magnesium you may experience diarrhea, nausea and possibly some cramping,” says Purdy.

If you’re taking a supplement, stick to the limit of 350 mg of supplemental magnesium per day unless your healthcare provider specifically suggests a higher dose, says Katy Dubinsky, Pharm.D., a pharmacist and the founder and CEO of Vitalize.

Symptoms and Signs

Common side effects of excessive magnesium intake include:

• Diarrhea
• Nausea
• Stomach cramps
• Low blood pressure
• Muscle weakness
• Irregular heartbeat
• Vomiting
• Facial flushing
• Retention of urine (an inability to empty all of the urine from your bladder)
• Depression
• Lethargy and muscle weakness
• Cardiac arrest

Who Is at Risk for a Magnesium Overdose?

While hypermagnesemia is rare, it’s something to keep in mind, particularly if you have a chronic illness. For example, if you have impaired kidney function or kidney failure, you may be at a higher risk for experiencing symptoms of a magnesium overdose.

Taking very high doses of magnesium, such as 5,000 mg found in some antacids and laxatives, have been associated with cases of magnesium toxicity. That doesn’t mean you should avoid these; instead, make sure you’re following the directions on the label when taking these medications.

Unfortunately, magnesium supplements may not mix well with other medications, including:

• Bisphosphonates (used to treat osteoporosis), which can decrease the absorption of magnesium in the body. 
• Certain antibiotics should be taken at least 2 hours before or 4 to 6 hours after a magnesium supplement.
• Diuretics can increase the loss of magnesium in urine and cause deficiency. 

When to See a Healthcare Provider

If you started taking a magnesium supplement and are experiencing the symptoms associated with magnesium toxicity above, call your healthcare provider. This is especially important if you have a kidney disorder.

Treatment and Prevention of Magnesium Overdose

To prevent a magnesium overdose, Dubinsky suggests focusing on food sources of magnesium. “Consumers should concentrate on including foods high in magnesium, such as leafy greens, nuts, seeds, whole grains, legumes and dairy products, in their diets to treat deficiency,” she says.

However, if buying a supplement is necessary and recommended by a medical professional, follow these tips from Dubinsky:

• Purchase high-quality supplements that have been tested for purity and effectiveness. Make sure your product has third-party testing.
• Choose forms of magnesium with high bioavailability, such as magnesium citrate.
• Don’t take more than 350 mg, the recommended daily upper limit unless a healthcare professional specifically recommends it. 
• Ask a healthcare professional if other medications or supplements you are taking could interact with a magnesium supplement. 

The Bottom Line

Magnesium is a necessary nutrient for a multitude of bodily functions including protein synthesis, muscle and nerve control, managing blood pressure and blood sugar and more. If you are deficient in magnesium, your healthcare provider might recommend taking a supplement. The tolerable upper intake limit is 350 milligrams of magnesium a day, and rare cases of overdose symptoms (like diarrhea, nausea and vomiting, muscle weakness, irregular heartbeat, low blood pressure) have occurred when a person consumes a very large dose of magnesium in a day.