I am not very scientific about this but clomid takes care of getting your body to start making its own test again and nolva takes care of the estro part, ,Hcg keeps the balls plump and makes it easier for you to recover,,a test only cycle I use the clomid, nolva combo and the Hcg is optional when you start adding deca and tren and shit like that the Hcg becomes more mandatory,,some of the vets can do a way better job of esplaining it but that's about it