What Is Neuroleptic Malignant Syndrome?

Medically Reviewed by Smitha Bhandari, MD on December 08, 2021
3 min read

Neuroleptic malignant syndrome (NMS) is a rare reaction to antipsychotic drugs that treat schizophrenia, bipolar disorder, and other mental health conditions. It affects the nervous system and causes symptoms like a high fever and muscle stiffness.

The condition is serious, but it’s treatable. Most people who get it make a full recovery when it’s found early.

NMS is very rare. Only about 1 to 2 out of every 10,000 people who take antipsychotic drugs get it.

All antipsychotic drugs can cause NMS. The older antipsychotic drugs include:

Doctors call the newer antipsychotic drugs "atypical antipsychotics." They include:

These drugs block a brain chemical called dopamine. That can make your muscles stiff and can cause rigid movements in people with Parkinson's disease.

Any antipsychotic drug can cause NMS. But stronger drugs, like fluphenazine and haloperidol, are more likely to trigger it.

NMS is more common in men than in women. You're also more likely to get it if you:

  • Take a high dose of the drug
  • Quickly increase your dose
  • Get the medicine as a shot
  • Switch from one antipsychotic drug to another

Some drugs used to treat nausea and vomiting can also cause NMS, because they block dopamine. These include:

People who take drugs for Parkinson's disease, like levodopa, can get NMS if they stop taking their medicine too quickly.

These often start within 2 weeks after you first take the medicine or have your dosage changed. Sometimes, they show up a few days after you start to take it. Or you might not have any until months later.

NMS symptoms usually last for 7 to 10 days. They may include:

  • High fever (102 to 104 F)
  • Muscle stiffness
  • Sweating a lot
  • Anxiety or other changes in mental state
  • Fast or abnormal heartbeat
  • Quick breathing
  • More saliva than usual

NMS can damage muscles and cause very high or low blood pressure. If you’re not treated, you can get serious problems, like:

  • Kidney failure
  • Heart and lung failure
  • Lack of oxygen in the body
  • Infection in the lungs caused by breathing in fluid (aspiration pneumonia)
  • More acid in the body


Your doctor will look for the two main symptoms of NMS: a high temperature and stiff muscles. To be diagnosed with it, you also need to have a few other warning signs, like a fast heartbeat, low or high blood pressure, and sweating.

Some other disorders have symptoms that are similar to NMS. To figure out if you have it, your doctor will do one or more of these tests:

  • Blood and urine tests
  • Brain imaging scans
  • Test of spinal fluid
  • EEG to find electrical problems in the brain 


Your doctor will first take you off the drug that caused this syndrome. Often, people with NMS get treatment in a hospital intensive care unit. The goal is to bring down your fever and give you fluids and nutrition.

Medicines used to treat NMS include:

If these medicines don't help, your doctor might try electroconvulsive therapy. During this treatment, you’re asleep and pain-free. A small electric current travels through your brain to trigger a seizure. This won’t hurt you, and it should help your symptoms.

NMS usually gets better in 1 to 2 weeks. After recovery, most people can start taking antipsychotic medicine again. Your doctor might switch you to a different drug.

NMS can come back after you’re treated. Your doctor will closely check for any signs of it. The longer you wait to go back on antipsychotic drugs, the less likely you'll be to get NMS again.