St. Johns Wort isn't a placebo. It really does work. I think, perhaps, your father just doesn't like the idea of you self medicating. But as with all herbal remedies, you can't take it for long periods of time without building up a tollerence. So, you take it for a week, then lay off for two or three days, then start taking it again.

Did you know that one of Paxils active ingredience is derived from St. Johns Wart?