Methotrexate is the most commonly prescribed drug for slowing the progression of rheumatoid arthritis.

Methotrexate belongs to the group of medicines known as antimetabolites. It is used to treat cancer of the breast, head and neck, lung, blood, bone, and lymph, and tumors in the uterus. It may also be used to treat other kinds of cancer, as determined by your doctor.

Methotrexate blocks an enzyme needed by the cell to live. This interferes with the growth of cancer cells, which are eventually destroyed. Since the growth of normal body cells may also be affected by methotrexate, other effects will also occur. Some of these may be serious and must be reported to your doctor. Other effects, like hair loss, may not be serious but may cause concern. Some effects may not occur for months or years after the medicine is used.

Methotrexate Side Effects
Methotrexate commonly causes nausea and vomiting. The most frequently reported methotrexate side effects include ulcerative stomatitis, leukopenia, nausea, and abdominal distress. Other frequently reported methotrexate side effects are malaise, undue fatigue, chills and fever, dizziness and decreased resistance to infection.

Dosing of Methotrexate
The dose of methotrexate will be different for different patients. The methotrexate dose that is used may depend on a number of things, including what the medicine is being used for, the patient's size, whether the medicine is being given by mouth or by injection, and whether or not other medicines are also being taken.
 

Caffeine and Methotrexate
Methotrexate may exert some of its anti-inflammatory effects by boosting tissue levels of a protein called adenosine. Given that caffeine can block the cell receptors that adenosine acts on, it is possible that it could also blunt methotrexate's effects. Studies in rats have indeed found that high doses of caffeine weakened methotrexate's actions, while some human studies have suggested it could have a similar effect in people.

does not appear to impair the effectiveness of methotrexate for treating rheumatoid arthritis (RA), Boston researchers report.