I took finasteride for a year and 4 months.
I didn't see any improvement at all with it and I do still have a decent amount of hair left (enough to hide any thinning except for a spot on the crown.)
I did have sides for a couple of months but they subsided for me. I was pretty brave at the time so I told myself I'd hold out for a year before quitting if sides persisted.
The reason I got off of it is because I was spending money to take a pill that alters some of my natural body chemistry with no guarantee of any result.
I know there's generic propecia and all, but I also don't have any way of knowing if finasteride (regardless of where I got it) even worked or not. I either wasn't a responder, or I didn't notice the results. What's to say I would've had less hair if I wouldn't have taken it for that year and 4 months?
I don't argue for or against it. People can do whatever they want, this is just the reason I chose to quit.