8 side effects of too much magnesium

In this article:

• Side effects of too much Mg
• Magnesium toxicity
• Supplement overdose vs. dietary excess
• Recommended daily allowance
• Navigating Mg intake

In this article

• Side effects of too much Mg
• Magnesium toxicity
• Supplement overdose vs. dietary excess
• Recommended daily allowance
• Navigating Mg intake

Magnesium is an essential mineral and electrolyte involved in hundreds of processes in your body. Among its health benefits: It supports nerve and muscle function, helps the body produce energy, helps regulate blood pressure, aids in controlling blood sugar levels, contributes to bone health, and even aids in producing DNA and RNA. In short, it’s a powerhouse.

While you can get magnesium from food sources like spinach, legumes, and brown rice, many people turn to supplements for the added benefit. Be advised: You can absolutely get too much of a good thing. In fact, it can be dangerous. Here, we’ll break down eight mild, severe, and sometimes, well, inconvenient, side effects of taking too much magnesium. 

8 side effects of too much magnesium

“When I first started taking magnesium, I took a higher dose before bed, thinking a little more would help me recover from working out. Wrong!” says Ashley Kitchens, RDN, registered dietitian and owner of Plant Centered Nutrition in Durham, North Carolina. 

There are many known side effects of taking too much magnesium, ranging from mild to extremely dangerous:

1. Diarrhea

“The most typical signs of too much magnesium are diarrhea and abdominal cramping,” says Erika Gray, Pharm.D., founder and chief medical officer at ToolBox Genomics.com. This happens because when magnesium doesn’t get absorbed, the excess sits in your intestines and pulls water into your bowels. This has a laxative effect, causing loose, runny stool. 

“The next morning after taking too much magnesium, I woke up, and my digestive system had very urgent opinions,” warns Kitchens. “This is why I recommend starting low and going slow, because it may save you an urgent trip to the bathroom.”

Not all magnesium is created equal. Using certain forms of magnesium, such as magnesium citrate, magnesium oxide, or magnesium hydroxide, can increase the risk of diarrhea due to their osmotic effects in the gut. If you already have bowel issues, talk to your provider about trying magnesium glycinate, which has a high absorption rate. 

2. Abdominal cramping, nausea, and vomiting

If you’re spared the diarrhea, you may still experience side effects like stomach cramps and nausea. In more severe cases, vomiting may occur. There are a few reasons this could happen. The first is that unabsorbed magnesium acts as an osmotic laxative, pulling water into your intestines. This can lead to bloating and cramping (and, eventually, diarrhea). 

The second reason you may feel nauseous after taking a magnesium supplement is that the mineral can sometimes irritate the lining of your stomach. The mineral also relaxes smooth muscles, including those in the gut. Slower gut motility can disrupt your normal digestion, potentially making you feel sick to your stomach (literally).  

3. Fatigue

If you live with chronic fatigue and stress, your medical provider might recommend taking magnesium. Fatigue and stress are highly connected, and research has shown magnesium may help reduce cortisol levels, especially among people with a magnesium deficiency.

On the flip side, taking too much magnesium can actually cause fatigue. Although the mineral may regulate gamma-aminobutyric acid (GABA), a neurotransmitter that slows brain activity, fatigue may be a sign of hypermagnesemia. High magnesium levels could lead to weakness, lethargy, and drowsiness, which may need medical attention. 

4. Low blood pressure

If you take magnesium and suddenly the room is spinning, it’s likely because the mineral has caused a drop in your blood pressure. This is a rare side effect, but it’s possible. Magnesium relaxes everything, including your blood vessels. Some people even take magnesium to prevent high blood pressure. Unfortunately, taking too much could lead to hypotension, which can cause confusion, dizziness, and even difficulty breathing. 

This is a potentially serious side effect of too much magnesium and something you should discuss with your healthcare provider.

5. Muscle weakness

Is too much relaxation a thing? Yes, it is, especially when it comes to your muscles. Magnesium relaxes your muscles, acting as a balance to calcium, which triggers muscle contractions. This balance is key for normal muscle movement.

Unfortunately, too much magnesium can have toxic effects, resulting in muscle weakness and slower reflexes. Magnesium toxicity is rare and a higher risk in people with kidney disease or those taking excessive amounts of magnesium.

6. Arrhythmia (irregular heartbeat)

Of the many hats magnesium wears, one of the most interesting is its role in regulating your heartbeat. The electrolytes magnesium, calcium, and potassium control the electrical signals in your heart:

• Calcium: Causes your heart to contract
• Potassium: Drives repolarization, also known as the electrical recovery of your heart between beats
• Magnesium: Helps counterbalance calcium and regulates intracellular potassium levels to ensure a stable rhythm

If you have too much magnesium in your system, it’s possible that the overload disrupts the timing of your heartbeats, leading to arrhythmias. In severe cases, this phenomenon could result in cardiac arrest.

7. Paralysis

In rare cases, too much magnesium can lead to paralysis. Magnesium plays a key role in the communication between your nerves and your muscles. However, when there is too much of the mineral present, that communication is interrupted, and even completely shut down. This can lead to a condition known as flaccid paralysis, which is a sudden onset of weak muscles. This is a medical emergency, especially if it happens with reduced reflexes or trouble breathing.

8. Death

Death from having too much magnesium is rare, but it can happen. One study followed more than 5,000 people with high plasma magnesium concentrations; of the 151 with hypermagnesemia, 36.9% died. 

Magnesium toxicity

There is a difference between taking more magnesium than your body can tolerate and developing a serious condition called hypermagnesemia. If you simply have a little too much magnesium, you might experience the milder symptoms mentioned, like nausea and diarrhea. 

“In a healthy person with normal kidney function, hypermagnesemia, or too much magnesium, is quite rare as the body pees out the excess magnesium,” says Dr. Erika Gray.

If you have hypermagnesemia, a blood test would reveal magnesium levels greater than 2.3 milligrams per deciliter (a normal range is 1.7 to 2.2 mg/dL). 

Hypermagnesemia symptoms start mild, with nausea, fatigue, and drowsiness, but as the condition progresses, you may experience:

• Dizziness and confusion
• Difficulty breathing
• Irregular heartbeat
• Cardiac arrest

There are a few populations that should use caution with high doses of magnesium, Dr. Gray warns: 

• Older adults who use magnesium-based laxatives such as milk of magnesia and/or antacids more than once a day in addition to oral magnesium
• People with kidney issues who may not be able to excrete excess magnesium
• Someone with pre-eclampsia, or persistent high blood pressure during pregnancy 
• Someone who experiences asthma exacerbations (attacks)

“Elderly people, asthmatics, or those with pre-eclampsia may end up taking magnesium doses of close to several grams of magnesium a day,” Dr. Gray explains. Any of these populations should use caution and get medical advice from a healthcare professional before taking large doses.

Supplement overdose vs. dietary excess

Can you overdose on magnesium from the food you eat? Almost certainly not. It comes down to how magnesium is delivered. Food provides it slowly and in smaller amounts, while supplements give you large, concentrated doses all at once. Additionally, taking magnesium with high-fiber foods containing phytate may reduce how well it’s absorbed.

“Some of the best sources of magnesium are pumpkin seeds, dark leafy greens like spinach, legumes like black beans and edamame, whole grains like quinoa and brown rice, and nuts like almonds and cashews,” says Kitchens. “If you’re eating a variety of whole, plant-based foods, you’re likely getting a decent amount of magnesium.”

The risk in magnesium overdose comes from high-dose supplements, which deliver a concentrated amount of the mineral to your body. These often come in forms meant to be absorbed quickly, adding to the risk of having too much in your body.

“It is virtually impossible to overdose on magnesium from whole food sources,” says Dr. Gray. “Caution should be used with taking magnesium supplements by the proverbial handful because of the osmotic effects of magnesium that can happen.”

Recommended daily allowance

The recommended daily allowance (RDA) for magnesium is 310 to 420 milligrams per day for adults. 

“There are several factors that affect how much magnesium you need, including age and biological sex,” registered dietitian Ashley Kitchens says. “We typically need more magnesium as we get older, and men generally need more magnesium than women. Magnesium needs also increase during pregnancy.”

RELATED: Best magnesium supplement for women

Certain medical conditions can deplete magnesium and increase what your body needs. For example, if you have Type 2 diabetes or Crohn’s disease, you may be at risk of a magnesium deficiency, so your provider may recommend you take more than the typical daily allowance. 

Your healthcare provider may recommend you take more caution if you have risk factors for accidental overdoses. For example, if you have health conditions like kidney disease, your kidneys may not be able to clear excess magnesium as efficiently. Some medications, including diuretics, can also interfere with magnesium absorption.

“I recommend double-checking with your doctor or dietitian if you have an underlying condition before starting a supplement,” Kitchens says.

Navigating your magnesium intake

How do you know if you’re taking enough magnesium? You can start by understanding the levels of magnesium in your body.

“Some people think that they need to take lots of magnesium because influencers and blogs often talk about magnesium deficiency,” Dr. Gray says. “A good strategy is to check a red blood cell magnesium level with your provider to understand how much magnesium is actually being absorbed. This is what we call a surrogate marker for intracellular magnesium, which is different from your typical serum magnesium test.” This can signal whether you have a true deficiency and potentially indicate how much of a supplement you may actually need. 

Dr. Gray and registered dietitian Ashley Kitchens also offer the following tips for taking magnesium: 

• Check the label on every supplement you take, not just a magnesium supplement, to assess how much you’re getting.
• If you’re new to magnesium, start with a lower dosage and increase it slowly.
• Split your daily dose into two to three doses a day to improve absorption and reduce the risk of diarrhea.

Dr. Gray also warns that you should have an understanding of elemental versus total magnesium. “For example, a label might say there are 1000 milligrams of magnesium malate, but looking closer, the elemental magnesium (the part that actually matters) might only be 150 milligrams. A good rule of thumb is that the elemental component is usually 11-15% of the total substance.” Still, the exact amount of elemental magnesium varies by form, so it’s best to check the Supplement Facts panel.

If you’re considering a magnesium supplement, start with food first. Talk to your healthcare provider to determine the right type and dosage.