Methotrexate is a prescription medicine used at very different doses for conditions such as rheumatoid arthritis, psoriasis, inflammatory bowel disease, ectopic pregnancy, and some cancers.

Key safety point: for inflammatory conditions, it is usually taken once weekly, never daily, unless a specialist has explicitly prescribed a different regimen. Taking it daily by mistake can cause life-threatening toxicity.

It can suppress bone marrow and affect the liver, lungs, kidneys, and immune system, so regular blood tests are required. Seek urgent medical care for fever or infection, mouth ulcers, unusual bruising/bleeding, severe vomiting or diarrhea, shortness of breath, or a new persistent cough. It must be avoided in pregnancy and requires specialist advice around conception.

What do you need to know about it: uses, dose schedule, side effects, interactions, monitoring, or a particular condition?