The short answer
Methotrexate is a type of chemotherapy called an antimetabolite. It blocks an enzyme cancer cells need to use folate, a vitamin required to build DNA, which stops fast-growing cells from multiplying. It is used to help treat leukemias, lymphomas, breast cancer, and other cancers, and is usually given as pills, an injection, or an IV infusion. Like all cancer medicines it can cause side effects; this page explains the common ones and the warning signs to report. It is educational only and not a substitute for your care team's advice.
Methotrexate is the generic name of this medicine.
It is a type of chemotherapy called an antimetabolite — it blocks an enzyme cancer cells need to use folate, a vitamin required to build DNA, which stops fast-growing cells from multiplying.
It is used to help treat leukemias, lymphomas, breast cancer, and some other cancers.
It is usually given as pills, an injection, or an IV infusion.
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The full explanation.
A folate blocker used at very different doses
Methotrexate is one of the oldest cancer medicines still in daily use. It blocks an enzyme that lets cells use folate. Folate is a B vitamin the body needs to build DNA. Without it, cells that divide fast cannot copy themselves.
The same drug treats very different things. A small weekly dose helps rheumatoid arthritis and severe psoriasis. Much larger doses, given in hospital, treat cancer. The gap between the two can be more than a hundredfold. That is why the details on your own prescription matter more than any general page.
Weekly, not daily: the dosing error in the boxed warning
The FDA boxed warning for methotrexate tablets says this plainly. Tablets taken once a day, when they were meant to be taken once a week, have caused deaths.
So check the label on your bottle. Say the schedule back to your pharmacist. If a relative helps with your pills, make sure they know the day too. Many teams write the day of the week on the box.
Which cancers it treats, and which form
The approved uses are not the same for every form of the drug.
Tablets are approved for acute lymphoblastic leukemia, as part of a combination maintenance plan. They are also approved for mycosis fungoides, and for non-Hodgkin lymphoma that has come back or has not responded.
The injection covers more ground. It is approved for acute lymphoblastic leukemia, for leukemia in the lining of the brain and spinal cord, for non-Hodgkin lymphoma, for osteosarcoma, for breast cancer, for squamous cell cancer of the head and neck, and for gestational trophoblastic neoplasia.
High doses and leucovorin rescue
Higher doses are given in hospital. The drug leaves the body through the kidneys, and a big dose can injure them on the way out.
So the team gives fluids through a drip. They add medicine to make your urine less acidic. They measure the drug level in your blood, sometimes for days. And they give leucovorin, a form of folate that protects healthy cells. This is called rescue. Its timing is exact, and doses are not moved or missed.
The rest of the boxed warning
Besides the dosing error, the boxed warning covers three things. Methotrexate can harm a pregnancy, including causing the death of the fetus. It can cause severe allergic reactions in people who have reacted to it before. And it can cause serious harm, including death, in the bone marrow, gut, liver, lungs, skin and kidneys.
Read the full wording on DailyMed. Then ask your team which parts apply to your dose and your health.
What to watch for at home
Mouth sores are common and can make eating miserable. Say something early, because there is a lot your team can do.
Medicines that do not mix well
Several ordinary medicines raise methotrexate levels in the blood. The label names aspirin and other anti-inflammatory painkillers, proton pump inhibitors for heartburn, penicillin and sulfa antibiotics, and probenecid.
That does not mean you can never take them. It means your pharmacist should check first. Keep one list of everything you take, including supplements, and bring it to appointments.
When to get help sooner
- Call 911 or go to an emergency department if you are struggling to breathe, a rash is blistering or peeling, or you realise you have taken the tablets daily instead of once a week.
- Call 911 or go to an emergency department if you have bleeding you cannot stop, or mouth sores so bad that you can no longer swallow fluids.
- Telephone your care team at once, whatever the hour, if your temperature is 100.4°F (38°C) or higher, or you have shaking chills. Methotrexate suppresses the bone marrow, and CDC calls a fever during cancer treatment a medical emergency. If you cannot get hold of them fast, go to an emergency department and tell staff you are on cancer treatment.
- Call your care team the same day if a cough is new, your urine is dark or much reduced, your skin or eyes yellow, or you vomit and cannot take a scheduled leucovorin dose.
- Call your care team within a day or two if mouth sores are making eating uncomfortable, your stools turn black or loose, or someone offers you an anti-inflammatory painkiller, an antacid tablet or an antibiotic that your pharmacist has not checked.
Sources
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=9b34b1d8-d125-41a2-9f6f-3fab67b573bd
- https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=0e30eaef-5a09-4104-8a11-c32933eadeab
- https://www.cancer.gov/about-cancer/treatment/drugs/methotrexate-sodium
- https://www.cdc.gov/cancer-preventing-infections/patients/fever.html
Words to know
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Common questions
What is Methotrexate?
Methotrexate is a type of chemotherapy called an antimetabolite. It blocks an enzyme cancer cells need to use folate, a vitamin required to build DNA, which stops fast-growing cells from multiplying. It is used to help treat leukemias, lymphomas, breast cancer, and some other cancers.
How is Methotrexate given?
It is usually given as pills, an injection, or an IV infusion. It can be given by mouth, as an injection, or into a vein, depending on the plan. Higher doses are given in the hospital with extra fluids and a 'rescue' medicine; follow your team's schedule closely. The exact schedule is set by your care team.
What are the common side effects of Methotrexate?
Commonly reported side effects include mouth sores, nausea, tiredness, low blood counts, and sensitivity to sunlight. Not everyone gets them, and many can be managed. Tell your care team about anything new or worsening.
Does Methotrexate cure cancer?
That depends on the person, the cancer type, and its stage. For some people a medicine like this can control cancer for a long time or be part of a curative plan; for others the goal is to slow the cancer or ease symptoms. Your care team can explain the goal in your situation.
Questions to ask your doctor
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Sources last checked: 2026-08-13 what this meansLast updated: 2026-08-18Next planned review: 2027-01-14
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How this page was created
Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes. We do not employ clinicians and do not intend to — our work is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Editorial review complete — This page completed Cancer Explained's editorial checks (sources, safety, plain language, duplication). It has not been reviewed by a physician or other healthcare professional.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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