Decreased serum ethinylestradiol conc w/ rifampicin, rifabutin, barbiturates, primidone, phenylbutazone, phenytoin, dexamethasone, griseofulvin, topiramate, some PIs, modafinil, St. John's wort, ritonavir, certain antibiotics eg, ampicillin, other penicillin & tetracyclines. Increased serum ethinylestradiol conc w/ atorvastatin, ascorbic acid, paracetamol, indinavir, fluconazole, troleandomycin. Increased plasma & tissue conc w/ cyclosporine, theophylline, corticosteroids. Decreased plasma & tissue conc w/ lamotigrine. Increased risk of galactorrhea w/ flunarizine. Increased risk of intrahepatic cholestasis w/ troleandomycin.