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Leucovorin comes in intravenous (IV), intramuscular (IM) injection (shot), and oral form.

How It Works

Leucovorin is a derivative of folic acid. Leucovorin works differently depending on whether it is used with methotrexate (MTX) or fluorouracil (5-FU).

  • Methotrexate: Leucovorin is given to "rescue" the gastrointestinal lining and bone marrow cells from MTX toxicity. Most of the complications and side effects of methotrexate can be either prevented or treated by using leucovorin, which is usually given 24 hours after methotrexate.
  • Fluorouracil: Leucovorin increases the effectiveness of 5-FU, increasing the anticancer effect.

Why It Is Used

Leucovorin is used with either methotrexate (MTX) for the treatment of ectopic pregnancy or fluorouracil (5-FU) for cancer treatment.

How Well It Works

Most of the complications and side effects of methotrexate can be either prevented or treated by using leucovorin, which is usually given 24 hours after the methotrexate is given.

Leucovorin enhances the binding of fluorouracil (5-FU) and prolongs the life span of 5-FU, increasing the anticancer effect.1

Side Effects

All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.

Here are some important things to think about:

  • Usually the benefits of the medicine are more important than any minor side effects.
  • Side effects may go away after you take the medicine for a while.
  • If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.

Call 911 or other emergency services right away if you have:

  • Trouble breathing.
  • Swelling of your face, lips, tongue, or throat.

Call your doctor if you have:

  • Hives.

Common side effects of this medicine when used with high-dose methotrexate or 5-FU include:

  • Swelling and redness of the lining of your mouth (stomatitis).
  • Nausea.
  • Vomiting.
  • Diarrhea.

See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)

What To Think About

Leucovorin is very well tolerated and has almost no side effects of its own.

Leucovorin generally decreases the severity of side effects of methotrexate (MTX). It can increase the severity of the side effects of 5-FU when used with that medicine.

Taking medicine

Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.

There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.

Advice for women

Do not use this medicine if you are pregnant, breast-feeding, or planning to get pregnant. If you need to use this medicine, talk to your doctor about how you can prevent pregnancy.


Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.

Complete the new medication information form (PDF)(What is a PDF document?) to help you understand this medication.



  1. Meyerhardt JA, Mayer RJ (2005). Systemic therapy for colorectal cancer. New England Journal of Medicine, 352(5): 476–486.


ByHealthwise Staff
Primary Medical ReviewerE. Gregory Thompson, MD - Internal Medicine
Specialist Medical ReviewerKenneth Bark, MD - Surgery, Colon and Rectal
Last RevisedAugust 27, 2012

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