they work together just fine. Proviron will still increase libido and finasteride will still block some of the DHT conversion. it does seem to be somewhat of a "cancel out" situation, but i've actually done them together and got the desired results.
Merck's website claims 1mg of finasteride reduces circulating DHT by 65% within 24 hours of oral dosing. that is both hard to believe and scary at the same time. the good news (or bad) is that it has a very short half life.
Nadr