It is well known that even 1/2 a grapefruit or one glass of juice can reduce an enzyme called cytochrome P450 (CYP 450) by 50% for up to 24 hours. This is important because some medications such as atorvastatin, amlodipine, carbamazepine and one of our newest medications for rheumatoid arthritis, tofacitinib (Xeljanz) need this enzyme to be eliminated from the body. read more →