• warfarin or other oral anti-coagulants (to thin the blood) • probenecid (for gout) • methotrexate (for certain types of cancer, psoriasis, rheumatoid arthritis) • theophylline (for breathing problems) • tizanidine (for muscle spasticity in multiple sclerosis) • clozapine (an antipsychotic) • ropinirole (for Parkinson’s disease) • phenytoin (for epilepsy)