i've only been taking finasteride for about 3 weeks, so this isn't a hugely developed opinion so far. but i'm 19 days into my finasteride treatment, i generally drink about 15 units a day, bit more on the weekends. i also smoke and believe in gay marriage, and i've still had 0 side effects. i haven't regrown all my old hair or anything like that, but my dick still works and i haven't got boobs so i figure you're probably FAIRLY safe.
but having said that, you're listening to the intoxicated opinion of a newcomer to finasteride. so take it with a pinch of salt or two.