What Is the Relationship between Methotrexate and Flu?

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  • Written By: C. K. Lanz
  • Edited By: O. Wallace
  • Last Modified Date: 09 September 2019
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Methotrexate and flu, or influenza, are a medication and potential side effect, respectively. Methotrexate is a medication that can cause serious side effects including suppression of the immune system. As a result, people taking this drug can be at a higher risk for infections like the flu. A healthy person’s immune system can usually fight off the flu but a suppressed immune system may not be successful. The flu or other infection can be fatal in such individuals.

This medication is normally given to treat serious conditions that have not responded to other treatments or to life-threatening cancer. Such conditions include severe psoriasis, severe active rheumatoid arthritis and cancers like breast, lung, and lymphoma. Methotrexate is an antimetabolite that slows the growth of cancer and skin cells. It can also slow immune system response, thus establishing a connection between methotrexate and flu or other potentially serious infections.

A healthy and normally-functioning immune system is usually able to respond and fight off infections like the flu. When a person’s immune system suppresses either due to medication or illness, the body cannot muster the same robust response. As a result, infections that are not serious for healthy people become life-threatening for the immunosuppressed. This is why many associate methotrexate and flu.


The flu is a viral infection that targets the respiratory system. Flu viruses change constantly and are spread in the air in droplets that can be inhaled or picked up by touching an object. Most healthy adults do not develop serious complications as the result of being infected.

Children and the elderly as well as those with chronic illnesses or a weakened immune system are at a greater risk of developing both the flu and its complications. Such complications include pneumonia, bronchitis, and sinus and ear infections. Pneumonia is the most common complication of the flu and can be fatal.

Symptoms of the flu include fever, muscle aches, and headache. Dry cough, fatigue, and nasal congestion are also common. The flu typically comes on suddenly and makes people feel worse than the common cold. People taking methotrexate that develop signs of the flu should contact the prescribing physician immediately.

In addition to the connection between methotrexate and flu, this drug can cause other serious side effects. The production of blood cells in the bone marrow can slow and liver and lung damage are possible. There is an increased risk of developing lymphoma or life-threatening skin reactions. Some patients also experience damage to the stomach, intestines, or the lining of the mouth. This medication can harm fetuses.

The most common side effects of methotrexate are dizziness, headache, and swollen gums. Many patients also experience hair loss, loss of appetite, and reddened eyes. Methotrexate and flu are linked because the possible effect of this medication on the immune system makes the patient more vulnerable to infections like the flu and their complications. Since the immune system is weak, the infection can be serious and even fatal.


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