Methotrexate
Methotrexate is a folate antagonist: it blocks the enzyme that regenerates active folate, which slows the turnover of rapidly dividing cells and dampens immune activity. At the low doses used outside oncology it acts as a disease-modifying anti-inflammatory drug. It is prescribed for autoimmune inflammation, and it is a prescription-only medicine.
It is a weekly medicine, never a daily one, and the weekly rhythm is the single most important thing about it; folic acid is given on the other days because the drug depletes folate. It can be taken with or without food. Alcohol adds to the liver burden and is avoided, and it is not used in pregnancy. Ibuprofen and diclofenac slow its clearance, sulfamethoxazole/trimethoprim adds a second antifolate on top of it, and omeprazole can also raise its levels; liver enzymes (ALT, AST), white cells, platelets and creatinine are checked on a regular schedule.
Mouth ulcers, unusual bruising or bleeding, fever or any sign of infection, persistent nausea, yellowing of the skin or eyes, or a new dry cough and breathlessness mean see a doctor rather than wait. The same applies to an accidental daily dose, or to pregnancy or a plan to become pregnant.
Reference information, not medical advice. Discuss any change with your doctor.