Methotrexate is used for the treatment of the following diseases-

Bladder Cancer	Leukemia	Psoriasis
Rheumatoid Arthritis	Lymphoma	Ectopic pregnancy

Rheumatoid Arthritis (RA) including Polyarticular Juvenile Idiopathic Arthritis (PJIA): 

• Adult RA: 7.5 mg once weekly.
• PJIA: 10 mg/m² once weekly.

Psoriasis:

• Single weekly oral, intramuscular, subcutaneous, or intravenous doses of 10-25 mg.

Acute lymphoblastic leukemia

• 20mg/m² of body size once a week. 

Non-Hodgkin lymphoma:

• 2.5 milligrams (mg) twice a week. As needed and tolerated, your doctor may adjust your dose. The dose, however, is usually no more than 10 mg per week.

Methotrexate can cause the following side effects-

Alopecia	Myelosuppression	Nausea
Headache	Diarrhea	Rash

• Methotrexate has been linked to serious toxic reactions and even death. Patients' bone marrow, liver, lung, skin, and kidney toxicity should be closely monitored.
• Methotrexate has the potential to cause embryo-fetal toxicity, including fetal death. Use is not advised during pregnancy . Advise men and women of reproductive age to use effective contraception during and after methotrexate treatment.
• With the concomitant administration of methotrexate (usually in high doses) and some nonsteroidal anti-inflammatory drugs, unexpectedly severe (sometimes fatal) bone marrow suppression, aplastic anemia, and gastrointestinal toxicity have been reported (NSAIDs).
• Methotrexate can cause interstitial pneumonitis at any time during treatment, even at low doses. Pulmonary symptoms (particularly a dry, ineffective cough) may necessitate treatment interruption and careful investigation.
• Hepatotoxicity, fibrosis, and cirrhosis may occur after prolonged use.
• Severe, occasionally fatal, skin reactions have been reported.
• Potentially fatal opportunistic infections may occur.
•  May cause impairment of fertility, oligospermia and menstrual dysfunction.
•  Mistaken daily use has led to fatal toxicity.
• Patients with impaired renal function, ascites, or pleural effusions: Elimination is reduced.
• Dizziness and fatigue: May impair ability to drive or operate machinery.