It is used to help 5-fluorouracil (5-FU) work better in treating colorectal, head and neck, or other cancers.

It can also be used as a cytoprotective (cell-protecting) agent. It can help protect normal cells in the bone marrow and digestive tract from damage from chemotherapy drugs such as methotrexate.

Your doctor may use leucovorin for other reasons as well.

The chemotherapy drug 5-fluorouracil (5-FU) works by binding to an enzyme needed for making DNA. Cancer cells that no longer have this enzyme available are more likely to die when they try to divide in two. Normally 5-FU binds it for only a short time, which limits how effective 5-FU can be. Leucovorin causes this binding to last for a longer period of time, which boosts the effect of 5-FU.

Chemotherapy drugs such as methotrexate work by preventing cells from using folic acid, which fast-dividing cells (like cancer cells) need to make DNA. Because some normal cells (like those in the bone marrow and digestive tract) also divide quickly, they can be harmed by these chemotherapy drugs. Leucovorin provides the normal cells with an alternate source of folic acid, which helps protect them.

• If you are allergic to any medicines, dyes, additives, or foods.

• If you are taking folic acid supplements or a multivitamin that contains folic acid. Ask your doctor if these may interfere with your treatment.

• If you have any medical conditions such as kidney disease, liver disease (including hepatitis), heart disease, congestive heart failure, lung disease, high blood pressure, diabetes, gout, or infections. You may need closer monitoring of these conditions while being treated.

• If you are pregnant, trying to get pregnant, or if there is any chance of pregnancy. It is not known if this drug might cause problems if either the male or female is taking it at the time of conception or during pregnancy. Men and women who are taking this drug should use some kind of birth control during treatment. It is important to check with your doctor about what kinds of birth control can be used with this medicine. This drug should be used during pregnancy only if the potential benefit is thought to justify the potential risk to the fetus.

• If you are breast-feeding. While no studies have been done, this drug may pass into breast milk and affect the baby. Talk with your doctor about the possible risks of breast-feeding while taking this drug.

• If you think you might want to have children in the future. It is not known whether or not this drug can affect fertility. Talk with your doctor about the possible risk with this drug and the options that may preserve your ability to have children.

• About any other prescription or over-the-counter medicines you are taking, including vitamins and herbs. In fact, keeping a written list of each of these medicines (including the doses of each and when you take them) with you in case of emergency may help prevent complications if you get sick.

No other serious interactions are known at this time. But this does not necessarily mean that none exist. Check with your doctor, nurse, or pharmacist about all of your medicines, herbs, and supplements, and whether alcohol can cause problems with this medicine.

It is very important to take leucovorin as directed by your doctor. If you are taking pills, store the medicine in a tightly closed container away from light, heat, and moisture and out of the reach of children and pets.

In rare cases, this drug can cause allergic reactions when the drug is given. Mild reactions may consist of skin rash or itching, fever, chills, or feeling flushed. More serious reactions happen rarely, but can be dangerous. Symptoms can include feeling lightheaded or dizzy (due to low blood pressure), chest pain or tightness, shortness of breath, back pain, or swelling of the face, tongue, or throat. Tell your doctor or nurse right away if you notice any of these symptoms during or after being given the drug.

• none known

• none known

• nausea
• skin rash
• allergic reaction (may include dizziness, shortness of breath, chest pain or tightness, swelling in the mouth or throat, hives, itching, flushing, or fever)*
• seizures

*See "Precautions" section for more detailed information.