Finasteride (the ingredient in propecia and proscar) inhibits 5 alpha reduction. In the case of testosterone, this is a good thing because it reduces to DHT, which is much more androgenic. In the case of nandrolone (which is what nordiol converts to) it reduces to DHN which is LESS androgenic.
Because of this fact, many people feel that you should not use 5ar inhibitors with nandrolone products. For the most part I disagree. Nandrolone in it's unreduced form is still less androgenic than test, so unless you're using a large amount of it, there's really no reason to be concerned. If using with a test product, then you will have much more problems from the test, then you would from nandrolone, so you still want to use the 5ar inhinbitor.
Nizoral may work by inhibiting DHT production, or it may be due to it's anti-inflamatory properties. Probably a combination of both. It will definitely help in this and other situations.