Magnesium: Benefits, Side Effects, Dosages, and Interactions


Magnesium is an essential mineral for overall physical health. About half of the magnesium in our body is found in bones. The rest help the cellular function of various body systems. Magnesium plays an important role in muscle function, heart rate, blood pressure, immune system function, and blood sugar levels.

Health benefits

Neuromuscular excitability

Magnesium is often used in a variety of cases related to overexcitation of the neuromuscular system.

This over-excitement of the neuromuscular system is common in people taking stimulant medications and can manifest itself in muscle spasms, clenched jaws, and teeth grinding. A review of several case studies points to the promise of oral magnesium supplementation for the relief of these latter symptoms, also known as bruxism .

Restless legs syndrome is a condition in which people feel like moving their legs. Taking magnesium supplements by mouth improved symptoms of restless leg syndrome in a study of 100 patients with type 2 diabetes .

Women who received magnesium salt intravenously had a 52% lower risk of subsequent seizures than those who received diazepam in a 2011 review of 1,687 women who experienced seizures after pregnancy .

Irritable bowel syndrome

Studies published in 2016 and 2017 showed that drinking magnesium sulfate-rich mineral water can improve bowel frequency in people with irritable bowel syndrome with constipation (IBS-C), but the effect has not been shown to last longer than six weeks.

This temporary laxative effect of magnesium appears to be due to two different mechanisms:

  • Muscle relaxation – Magnesium can relax the intestinal muscles, which can help establish a smoother flow as stool passes through the intestines.
  • Stool Softeners: Magnesium draws water into the intestines, acting as an osmotic laxative . This increased amount of water stimulates intestinal motility . It also softens and increases stool size, triggers bowel movements, and helps facilitate bowel movements.

Possible side effects.

Get Medical Information / Cindy Chang

The most common side effect of magnesium is diarrhea, which can cause:

  • Dehydration
  • Nutritional deficiency
  • Weightloss
  • An electrolyte imbalance with potentially serious consequences for the heart, muscles, and respiration.


Toxic amounts of magnesium can cause kidney problems and serious side effects that affect the gut. A condition called ischemic colitis has been described, which can cause permanent damage to the intestines as a result of magnesium poisoning. Read product labels carefully to avoid excessive magnesium intake.

Drug interactions

Magnesium supplementation can affect the effectiveness of some prescription medications. Before you start taking magnesium, tell your doctor and pharmacist if you are taking any of the following:

  • Laxatives
  • Vitamin supplements
  • Diuretics
  • Chemotherapy drugs
  • Medications for osteoporosis
  • Thyroid medications
  • Certain antibiotics such as ciprofloxacin and moxifloxacin.
  • Antacids

In some cases, drug interactions can be minimized by separating the magnesium from the co-prescribed drug for four to six hours. In other cases, your healthcare provider may need to change or adjust the dose of the jointly prescribed drug.


Your kidneys are directly responsible for removing magnesium from your bloodstream, so you should not take vitamin and mineral supplements (unless prescribed by your healthcare provider) if you have kidney disease or need dialysis, as even normal amounts can cause toxicity.

If you are using magnesium to treat constipation due to IBS-C, you should be aware that the dose of magnesium used to treat constipation should not be used as a dietary supplement.

If your kidneys are damaged, taking too much magnesium can lead to an abnormal build-up called hypermagnesemia. This, in turn, can lead to irregular heart rhythms, respiratory failure, and even cardiac arrest.

Dosage and preparation

The National Institutes of Health (NIH) have published a fact sheet that describes the recommended daily intake of magnesium . The recommended amount depends on age, and different recommendations are offered for pregnant and lactating women. This is the total and includes the dietary intake of magnesium.

You can take magnesium in vitamin tablet form, in prepared liquid form, or in powder form mixed with a liquid. Magnesium supplements come in many different forms, each combined with a different chemical. These combinations of magnesium salts are absorbed by the small intestine at different rates. As a result, each supplement differs in the rate at which it can meet the magnesium requirement and therefore has a different dose threshold required to experience the effects.

This makes it difficult to understand whether a lower dose used in a clinical trial of a salt-based drug would be effective for someone trying to replicate the effects with another drug. If the dose used in both studies is sufficient to meet the magnesium requirement, the effects are likely to be comparable. Keep this in mind when interpreting test results and consult your physician before beginning any treatment regimen.

What to look for

Checking the additive label on the back of the magnesium package will allow you to verify the active dose per serving, as well as any other ingredients that may be included, such as flavors, fillers, or binders.

Third-party testing organization ConsumerLab investigated 40 popular magnesium supplements on the market and found that some of them degrade quickly when exposed to moisture, some contain harmful amounts of lead, and some are mislabeled based on their content. It would be a good idea to test a specific manufacturer through one of these third-party testing sites to make sure you can trust what you see on the label.

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