How to Tell If You're Taking Too Much Magnesium

Medically reviewed by Suzanne Fisher, RD

Magnesium is an essential mineral that’s important for literally hundreds of bodily functions including muscle function, blood sugar control, and blood pressure regulation. About half of Americans don’t get enough magnesium from food and beverages alone, so supplements could be helpful to fill in the gaps of your magnesium intake.

However, supplements often come in much higher doses than what you’d get from foods, so the risk of magnesium overdose (or hypermagnesemia) is much higher. At best, magnesium overdose can cause diarrhea and abdominal cramps, but at worst it could lead to difficulty breathing, irregular heartbeat, and death. Severe magnesium toxicity isn’t all that common, but symptoms like diarrhea are more common if you’re taking a high dose supplement.

In this article, learn how much magnesium is safe to take, symptoms of a magnesium overdose, and what to do if you think you’ve taken too much magnesium.

How Much Magnesium Is Safe to Take?

Magnesium does so much for our bodies, so it’s important to consume enough of it. Amongst hundreds of other functions, we need magnesium to turn food into energy and to generate protein. You can find it in foods like nuts, seeds, green leafy vegetables, and whole grains, but if you don’t eat those foods very much then a supplement can help you meet your magnesium needs. Magnesium supplements may also help with migraines, constipation, anxiety, and sleep.

The amount of magnesium you need each day depends on your age, sex, and whether you’re pregnant or lactating. Keep in mind that the recommendations below are for total intake of magnesium from foods and supplements combine:

• Birth to 6 months: 30 milligrams (mg)

• 7–12 months: 75 mg

• 1–3 years: 80 mg

• 4–8 years: 130 mg

• 9–13 years: 240 mg

• 14–18 years: 410 mg for males; 360 mg for females; 400 mg if pregnant; 360 mg if lactating

• 19–30 years: 400 mg for males; 310 mg for females; 350 mg if pregnant; 310 mg if lactating

• 31–50 years: 420 mg for males; 320 mg for females; 360 mg if pregnant; 320 mg if lactating

• 51+ years: 420 mg for males; 320 mg for females

To prevent a magnesium overdose, it’s important to be aware of the tolerable upper intake levels (ULs) for magnesium. These are purely for magnesium supplements, not foods, and they vary based on your age.

• Birth to 12 months: none established

• 1–3 years: 65 mg

• 4–8 years: 110 mg

• 9–18 years: 350 mg

• 19+ years: 350 mg

Side Effects of Magnesium

Taking a magnesium supplement could cause some unpleasant side effects, even if you’re not exceeding the UL. Diarrhea is one of the most common side effects since magnesium can draw water into the stool to soften the stool. These digestive side effects are more likely with magnesium oxide or magnesium citrate since these forms are commonly used for treating constipation.

Symptoms of Magnesium Overdose

The symptoms of magnesium overdose can be quite severe because of all the roles magnesium plays in the body. In fact, overdosing on magnesium can lead to muscle paralysis and serious cardiac issues like cardiac arrest.

Earlier signs of magnesium overdose include nausea, dizziness, weakness, and confusion. If magnesium levels continue rising, symptoms like slowed reflexes, headache, flushing, and blurred vision can occur.

Who Is at Risk for Magnesium Overdose?

Magnesium overdose actually isn’t that common, but certain groups are at higher risk of magnesium overdose. They include:

• Those with impaired kidney function: The kidneys help excrete magnesium, so those with acute kidney injury or chronic kidney disease are more likely to experience magnesium overdose.

• Those taking magnesium supplements: Not surprisingly, consuming high doses of supplemental magnesium—often for treating constipation—makes it more likely you’ll overdo it.

• Those taking certain medications: Some medications, like anticholinergics or opioids, can increase magnesium absorption, which increases the chance of a magnesium overdose.

• Pregnant people with eclampsia: Since high doses of intravenous magnesium are commonly used to help prevent eclamptic seizures, pregnant people with eclampsia are considered a high-risk group for magnesium overdose.

When to See a Healthcare Provider

If you’re taking a magnesium supplement or have impaired kidney function and you experience any symptoms of a magnesium overdose, speak with a healthcare provider. Mild magnesium overdose often doesn't lead to symptoms, so if you experience symptoms your magnesium levels may have already progressed to a moderate magnesium overdose. It’s better to act early to prevent it from progressing to a severe overdose.

In general, it’s best to talk with your healthcare provider before starting a magnesium supplement, especially if you’re taking other supplements or medications. They can make sure there aren’t any drug or supplement interactions to be aware of and recommend an appropriate dose. If you have impaired kidney function then you’ll definitely want to consult with your healthcare provider first since you’re at higher risk for a magnesium overdose.

How Is Magnesium Overdose Diagnosed?

To check for a magnesium overdose, your healthcare provider will likely draw blood to check your serum magnesium level. Normal levels are generally around 1.8–2.3 mg/dL. The severity of a magnesium overdose is categorized as follows:

• Mild magnesium overdose: less than 7 mg/dL

• Moderate magnesium overdose: 7–12 mg/dL

• Severe magnesium overdose: more than 12 mg/dL

However, since checking blood magnesium levels isn’t all that routine and symptoms of a magnesium overdose aren’t all that unique, it may be overlooked initially. So diagnosis often involves a process of elimination for other neurological and cardiorespiratory conditions like acute kidney failure, hypothyroidism, and high potassium levels.

Treatments for Magnesium Overdose

The treatment for magnesium overdose depends on the severity. If you have a mild magnesium overdose and normal kidney function, the typical treatment is simply to stop taking any magnesium supplements to give your body time to excrete the excess magnesium.

However, if you have a severe magnesium overdose, you may need to be hospitalized so your heart function and blood pressure can be closely monitored. At the hospital, they may administer calcium and saline intravenously since calcium can help offset magnesium’s effect on the heart and muscles. If it’s really severe, you may also be given intravenous diuretics or even hemodialysis to help your body get rid of the excess magnesium faster.

With that in mind, people at high risk for magnesium overdose, particularly those with impaired renal function, likely don’t need a magnesium supplement since the kidneys will have a hard time excreting the excess.

How to Prevent Magnesium Overdose

Magnesium overdose is dangerous, but remember that it’s not very common, especially if you have normal kidney function. If you have normal kidney function, then taking a magnesium supplement within recommended daily doses is likely safe and may even benefit your health. Just be sure to speak with a healthcare provider about a safe dose, and try purchasing a third-party tested supplement so you know the dosage listed is accurate.

If you’re at high risk for magnesium overdose, speak with a healthcare provider before starting a magnesium supplement to be sure it’s safe for you to start taking. Your healthcare provider may check your magnesium levels more often if they suspect they may be abnormal.

That being said, the best way to boost your magnesium intake is by eating more magnesium-rich foods like dark leafy greens, nuts, and seeds. These foods have other nutrients like antioxidants and fiber that magnesium supplements don’t have, and eating magnesium-rich foods doesn’t pose much of a risk for a magnesium overdose.

A Quick Review

As important as magnesium is for the body, too much of it can lead to some pretty serious health issues. Eating more magnesium-rich foods isn’t usually cause for concern, but taking high-dose supplements could increase your risk for magnesium overdose. The best way to prevent a magnesium overdose is to consult with your doctor or registered dietitian before starting a supplement to be sure that it’s safe for you to take and that you take an appropriate dose. 

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