EE is known to inhibit several cytochrome P450 enzymes, including CYP1A2, CYP2B6, CYP2C9, CYP2C19, and CYP3A4, and is possibly an inducer of CYP2A6. As a result, it can affect the metabolism and concentrations of many other drugs. Examples of known interactions include bupropion, caffeine, mephenytoin, midazolam, nicotine, nifedipine, omeprazole, propranolol, proguanil, selegiline, theophylline, and tizanidine. One of the most notable interactions is that EE strongly increases levels of selegiline, a substrate of CYP2B6 and CYP2C19. EE may also induce glucuronidation and possibly alter sulfation. It has been found to increase the clearance of and reduce the concentrations of a variety of drugs known to be glucuronidated. Examples include clofibrate, lamotrigine, lorazepam, oxazepam, and propranolol.