depends
Propecia is finasteride. Dutasteride is a very similar drug that works at the scalp a little more directly. The will inhibit the process that converts test to dht. It can be used in test cycles.
However, it is a bad idea to take with deca, and will actually make hair loss worse.
I know peole take it on test cycles when they are using other compounds (like d-bol or eq), but other than ok with test, not ok with deca, I'm not sure which AAS it is really compatable with.