As with all medications, methotrexate can sometimes cause side-effects. Methotrexate may cause nausea (feeling sick), vomiting, diarrhoea, mouth ulcers, hair loss (usually minor) and skin rashes.
It can also affect the blood (causing fewer blood cells to be made) and your liver. You'll therefore need to have blood tests before starting methotrexate and at regular intervals while you're taking it. You may be asked to keep a record of your blood test results in a booklet, and you should take it with you when you visit your GP or the hospital.
Methotrexate can affect the lungs so you'll have a chest X-ray before starting it. Patients suffering from long-term lung diseases like fibrosis or emphysema are often not suitable for methotrexate.
You must not take methotrexate unless you’re having regular blood checks. These are usually done every two weeks when you start on methotrexate and the dose is being built up, then every six weeks when you are on a stable dose. Because methotrexate affects the immune system, it can make you more likely to develop infections. You should tell your doctor or nurse specialist straight away if you develop any of the following after starting methotrexate:
- a sore throat, fever or any other signs of infection
- shortness of breath
- unexplained bruising or bleeding
- yellowing of the skin or eyes (jaundice)
- any other new symptoms or anything else that concerns you.
You should stop methotrexate and see your doctor immediately if any of these symptoms are severe or you’re becoming very unwell.
You should also see your doctor if you develop chickenpox or shingles or come into contact with someone who has chickenpox or shingles.
These infections can be severe in people on methotrexate. You may need antiviral treatment, and you may be advised to stop taking methotrexate until you're better.
In rare cases, methotrexate causes inflammation of the lung with breathlessness. If this happens to you, see your doctor.
Most doctors prescribe folic acid tablets to patients who are taking methotrexate as this can reduce the likelihood of side-effects. Some doctors advise that it shouldn't be taken on the same day as methotrexate.
Reducing the risk of infection
- Try to avoid close contact with people with severe active infections.
- For advice on avoiding infection from food, visit the NHS Choices Food Poisoning website.