Methotrexate may cause very serious side effects. Some side effects of methotrexate may cause death. You should only take methotrexate to treat life-threatening cancer, or certain other conditions that are very severe and that cannot be treated with other medications. Talk to your doctor about the risks of taking methotrexate for your condition.

Tell your doctor if you have or have ever had excess fluid in your stomach area or in the space around your lungs and if you have or have ever had kidney disease. Also tell your doctor if you are taking nonsteroidal anti-inflammatory drugs (NSAID) such as aspirin, choline magnesium trisalicylate (Tricosal, Trilisate), ibuprofen (Advil, Motrin), magnesium salicylate (Doan's), naproxen (Aleve, Naprosyn), or salsalate. These conditions and medications may increase the risk that you will develop serious side effects of methotrexate. Your doctor will monitor you more carefully and may need to give you a lower dose of methotrexate or stop your treatment with methotrexate.

Methotrexate may cause a decrease in the number of blood cells made by your bone marrow. Tell your doctor if you have or have ever had a low number of any type of blood cells or any other problem with your blood cells. Your doctor may tell you not to take methotrexate unless you have life-threatening cancer. Call your doctor immediately if you experience any of the following symptoms: sore throat, chills, fever, or other signs of infection; unusual bruising or bleeding; excessive tiredness; pale skin; or shortness of breath.

Methotrexate may cause liver damage, especially when it is taken for a long period of time. If you drink or have ever drunk large amounts of alcohol or if you have or have ever had liver disease, your doctor may tell you not to take methotrexate unless you have a life-threatening form of cancer because there is a higher risk that you will develop liver damage. The risk that you will develop liver damage may also be higher if you are elderly, obese, or have diabetes. Tell your doctor if you are taking any of the following medications: acitretin (Soriatane), azathioprine (Imuran), isotretinoin (Accutane), sulfasalazine (Azulfidine), or tretinoin (Vesanoid). To decrease the risk of developing liver damage, do not drink alcohol while you are taking methotrexate. Call your doctor immediately if you experience any of the following symptoms: nausea, extreme tiredness, lack of energy, loss of appetite, pain in the upper right part of the stomach, yellowing of the skin or eyes, or flu-like symptoms. Your doctor may order liver biopsies (removal of a small piece of liver tissue to be examined in a laboratory) before and during your treatment with methotrexate.

Methotrexate may cause lung damage. Tell your doctor if you have or have ever had lung disease. Call your doctor immediately if you experience any of the following symptoms: dry cough, fever, or shortness of breath.

Methotrexate may cause damage to the lining of your mouth, stomach or intestines. Tell your doctor if you have or have ever had stomach ulcers or ulcerative colitis (condition in which part or all of the lining of the intestine is swollen or worn away). If you experience any of the following symptoms, stop taking methotrexate and call your doctor right away: mouth sores, diarrhea, black, tarry, or bloody stools, or vomit that is bloody or looks like coffee grounds.

Taking methotrexate may increase the risk that you will develop lymphoma (cancer that begins in the cells of the immune system). If you do develop lymphoma, it might go away without treatment when you stop taking methotrexate, or it might need to be treated with chemotherapy.

If you are taking methotrexate to treat cancer, you may develop certain complications as methotrexate works to destroy the cancer cells. Your doctor will monitor you carefully and treat these complications if they occur.

Methotrexate may cause serious or life-threatening skin reactions. If you experience any of the following symptoms, call your doctor immediately: fever, rash, blisters, or peeling skin.

Methotrexate may decrease the activity of your immune system, and you may develop serious infections. Tell your doctor if you have any type of infection and if you have or have ever had any condition that affects your immune system. Your doctor may tell you that you should not take methotrexate unless you have life-threatening cancer. If you experience signs of infection such as a sore throat, cough, fever, or chills, call your doctor immediately.

If you take methotrexate while you are being treated with radiation therapy for cancer, methotrexate may increase the risk that the radiation therapy will cause damage to your skin, bones, or other parts of your body.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests before, during, and after your treatment to check your body's response to methotrexate and to treat side effects before they become severe.

Tell your doctor if you or your partner is pregnant or plan to become pregnant. If you are female, you will need to take a pregnancy test before you begin taking methotrexate. Use a reliable method of birth control so that you or your partner will not become pregnant during or shortly after your treatment. If you are male, you and your female partner should continue to use birth control for 3 months after you stop taking methotrexate. If you are female, you should continue to use birth control until you have had one menstrual period that began after you stopped taking methotrexate. If you or your partner become pregnant, call your doctor immediately. Methotrexate may harm the fetus.