I am on all the time. I take proviron (50 mg ed) and I never have problems. It doesn't hurt your liver, and it allows more free test to ciruculate, so you get more bang for your test. You could probably take 25 mg a day.
My liver values are a bit above normal (which is actually normal for a weigth lifter). I also take lipitor and accutane (which are hard on your liver), and my doc isn't concerned with my liver values. But I *do* get my liver values tested monthly. So my point with this is that your liver may be absolutely fine with a lot of shit in your blood, but you shoudl get it tested regularly to be sure.