<unk>  is metabolized by certain cytochrome P450 isoforms, including CYP3A4 and CYP2C9. Thus, inducers of enzymes such as CYP3A4 can decrease circulating concentrations of<unk> . Examples of inducers include anticonvulsants like phenytoin, primidone, ethosuximide, phenobarbital, and carbamazepine; azole antifungals like fluconazole; and rifamycin antibiotics like rifampin (rifampicin). Conversely, inhibitors of CYP3A4 and other cytochrome P450 enzymes may increase circulating levels of<unk> . An example is troleandomycin, which is a potent and highly selective inhibitor of CYP3A4. Paracetamol (acetaminophen) has been found to competitively inhibit the sulfation of<unk> , with pretreatment of 1,000 mg of paracetamol significantly increasing the AUC levels of<unk>  (by 22%) and decreasing the AUC levels of<unk>  sulfate <unk>  sulfate) in women. The same has been found for ascorbic acid (vitamin C) and<unk> , although the significance of the interaction has been regarded as dubious. In contrast to estradiol, it is unlikely that there is a pharmacokinetic interaction between smoking (which potently induces certain cytochrome P450 enzymes and markedly increases the 2-hydroxylation of estradiol) and<unk> . This suggests that estradiol and<unk>  are metabolized by different cytochrome P450 enzymes. There is, however, an increased risk of cardiovascular complications with smoking and<unk> , similarly to the case of smoking and other estrogens.<unk>  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<unk>  strongly increases levels of selegiline, a substrate of CYP2B6 and CYP2C19.<unk>  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. Progestins, which are often used in combination with<unk> , are also known to inhibit cytochrome P450 enzymes, and this may contribute to drug interactions with<unk> -containing contraceptives as well. Examples include gestodene, desogestrel, and etonogestrel, which are CYP3A4 and CYP2C19 inhibitors. In addition, these progestins are known to progressively inhibit the metabolism of and increase concentrations of<unk>  itself.
Ethinylestradiol
Vinyltestosterone
Haloprogesterone
Ethyltestosterone
Progestogen
Progestogen 
Methylestradiol
Cloxestradiol acetate