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A box of epsom salts and a bottle of magnesium sulfate supplements are crossed out with a giant red NO circle.

Magnesium Sulfate and Myasthenia Gravis

Reviewed by: HU Medical Review Board | Last reviewed: March 2024

Myasthenia gravis (MG) is an autoimmune disorder that can cause symptoms like muscle weakness and fatigue. Certain drugs or treatments can make the symptoms of MG worse. Magnesium sulfate is one such example. People with MG should not use magnesium sulfate as a treatment or alternative therapy.1,2

What is magnesium sulfate?

Magnesium sulfate is commonly found as Epsom salt. It is a white powder that can be dissolved in water. People often add it to baths to relax sore muscles. Some people also may use it as a laxative by dissolving it in water.3

Magnesium sulfate does not require a prescription. But everyone should talk to a healthcare provider before they start using a magnesium sulfate product. This is because it may negatively interact with other medicines or conditions.2,3

Furthermore, people with MG should avoid using magnesium sulfate because it can make their symptoms worse. It can increase muscle weakness and make it harder to control their muscles.2,3

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Magnesium sulfate as a treatment

Other than creating relaxing baths, magnesium sulfate is also used in hospitals and clinics to treat seizures. A magnesium sulfate solution can be injected to stop a seizure.4

Seizures can be caused by different health conditions. For example, eclampsia is when pregnant people with high blood pressure have seizures. Magnesium sulfate is the suggested treatment for stopping seizures in people with eclampsia.5

However, magnesium sulfate should not be used to treat seizures in people living with MG. This can make it tricky to treat people with both MG and eclampsia. But the benefits of magnesium sulfate injections as a seizure treatment do not outweigh the possible side effects for people with MG. Other seizure treatments are recommended for people with MG.2,4

How can magnesium sulfate make MG worse?

What makes magnesium sulfate a good treatment for seizures is also what makes it harmful to people with MG.6,7

During a seizure, the brain starts sending a high number of electrical signals to the nerves near the muscles. The muscles receive these signals and begin to cause uncontrolled muscle movements. Magnesium sulfate blocks these signals from going between nerves near the muscles and surrounding nerves, as well as between nerves and muscles. This stops the seizure because of the nerve-nerve communication being stopped.6,7

In people with MG, the connection between the nerves and the muscles is already weak. When magnesium sulfate blocks nerve signals from reaching the muscles, muscle weakness increases and it becomes harder to control those muscles. This can be very harmful. It can even affect the muscles used for breathing, making it hard to breathe.8

The side effects of using magnesium sulfate in people with MG may include:4

  • Muscle weakness
  • Fatigue
  • Uncontrolled movement of a facial muscle (facial twitch)
  • Abnormal heartbeat (arrhythmia)
  • Difficulty breathing

Other things to know

Treating seizures with magnesium sulfate injections can be very harmful for people with MG. Make sure your healthcare team knows about your MG diagnosis and all the drugs you are taking.2

A small amount of magnesium sulfate from Epsom salt baths or magnesium supplements may not be harmful to those with MG. But talk with your doctor before using anything that contains magnesium sulfate. Your doctor can tell you about the possible side effects and help you make an informed decision.2

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