Step 1: DMARDs (disease modifying antirheumatic drugs) slow the progression of rheumatoid arthritis rather than just relieving pain. They include methotrexate, sulfasalazine, chloroquine or hydroxychloroquine, leflunomide, azathioprine, cyclosporine, gold salts and d-penicillamine, plus biologics.
Step 2: Chloroquine, azathioprine and leflunomide are all recognised DMARDs, so they are not the answer.
Step 3: Vincristine is a vinca alkaloid anticancer agent that inhibits microtubule assembly. It is used in leukaemias and lymphomas, not as a DMARD.
Step 4: Therefore vincristine is the drug that does not belong, making it the correct choice.