How long until Deca becomes inactive?

when is Deca officially dead? When is it no longer functioning in you body? . . . . The reason I ask is because I want to take Propecia (finasteride) for my hair b/c I've noticed some fallout. I have read that Deca and finasteride are a bad combination. So I am wondering when the Deca is no longer functioning so that I can start the finasteride.

I heard 18 months for Deca

18 months is the detection time i.e. the length of time metabolites remain in your system, im almost certain it will remain active for about 4 weeks, but if you do a serach im sure someone knows for certain.

Anyone else on this? That knows for sure?