From Brock Strasser
If you use Deca, you shouldn't use Propecia. Here's why. Propecia is a 5-a-reductase inhibitor. It prevents testosterone from becoming DHT. Compared to testosterone, DHT is more androgenic and tougher on the hairline. Deca is 5-a-reduced to DHN (dihydronandrolone). DHN is less androgenic than nandrolone. You'd want this to happen to save the hairline or minimize the androgenic insult to it. Propecia would prevent this from happening.