The Tensilon test was used to help diagnose myasthenia gravis from the 1930s until 2018, when the FDA discontinued its use. It was stopped mainly because of the high number of false positive results.

In 2018, the FDA discontinued approval for the Tensilon test to diagnose a condition called myasthenia gravis (MG). That means insurance companies no longer cover this test, and your doctor will order different tests if they suspect that you have MG.

You may still hear about this test, so here’s more information about it. During a Tensilon test, the doctor used a drug called Tensilon (edrophonium) to determine if an individual had MG. Tensilon prevents the breakdown of the chemical acetylcholine, a neurotransmitter that nerve cells release to stimulate your muscles. If an individual had MG, they wouldn’t have a typical reaction to acetylcholine.

A person tested positive for MG if their muscles got stronger after being injected with Tensilon.

Today, doctors use blood tests, imaging tests, and an electrical test called electromyography to diagnose MG.

Read more: Myasthenia gravis »

A Tensilon test was done if a doctor suspected an individual might have MG and to monitor the effectiveness of some medications used to treat MG.

Before the test, your doctor might set dietary restrictions or ask an you to stop using certain medications or supplements.

The test lasted around 30 minutes and started with an intravenous (IV) injection of a small amount of Tensilon. Then, the individual being tested was asked to perform a repetitive movement like standing up and sitting down in a chair, crossing and uncrossing their legs, or holding their arms overhead until they got tired. When they tired, they were given another dose of Tensilon. If the individual got stronger after the Tensilon dose, they might have MG.

Yes. The Tensilon test had a number of usually short-term side effects, like:

Rarely some people had serious side effects such as breathing failure or abnormal heart rhythms. For this reason, the test could only be performed in places where emergency resuscitation equipment was available.

It was also not used for people who had certain conditions like:

Today there are more accurate tests for myasthenia gravis with fewer risks. Now MG is diagnosed with one or more of these:

Blood tests

Blood tests measure levels of antibodies in your blood that stop signals from traveling between muscles and nerves. If these antibodies are present, it means an individual has MG.


This electrical nerve test measures how well your nerves function. A small needle is inserted into muscles, usually around your eyes, in your forehead, or in your arms. These needles measure the electrical signals muscles send. If the signals are interrupted, it may be a sign of MG.

Imaging tests

Imaging tests like MRI or CT scan may be done to look at your thymus gland, which is located in your chest. If your thymus gland is bigger than usual, it may be a sign of MG. Imaging tests may also be used to see if something else, like a change in your brain, is causing your symptoms.

Is the Tensilon test still used?

Tensilon testing is no longer used to diagnose MG in the United States and many other countries. Now blood tests, imaging, and nerve tests are used instead.

Is the medication Tensilon (edrophonium) used today?

Yes, but very rarely. Tensilon (edrophonium) may be used to reverse the effects of a nerve block mediation used in some surgeries.

A Tensilon test was once the main test used to diagnose MG. However, in 2018, the FDA discontinued its approval for use in this way. Now blood tests, nerve tests, and imaging tests are used to diagnose MG and to help in treatment planning.