I've done many searches on this subject both on the boards and the general internet. Additionally after my last cycle I used proviron at 50mg pd, quitting use after 4 weeks post cycle. One week later my test levels tested well within normal 510. So it is at least my opinion from research and experience that while it may effect test levels slightly, it is in fact very slight and worth the use post cycle. Proviron definitely helps me post cycle, totally eliminating depression, mood swings, sex drive problems, and as an anti-e.