Phenytoin, barbiturates, primidone, carbamazepine, rifampicin, oxcarbazepine, topiramate, felbamate, ritonavir, griseofulvin, products containing St. John's wort, cyclosporin, lamotrigine, melatonin, drugs that increase serum K levels (angiotensin-II-receptor antagonists, K-sparing diuretics & aldosterone antagonists). HIV/HCV protease inhibitors non-NRTIs can increase or decrease plasma conc of estrogen or progestin. Drospirenone causes an increase in plasma renin activity & plasma aldosterone induced by its mild antimineralocorticoid activity.