Going from the 1990 in your username, I am going to go ahead and say GH is a waste of money for a 20-21 year old. You can get a lot more bang for your buck spending the money other ways.
BUT I would do just 4iu a day if you are cutting unless you have an unlimited supply of money, GH works better over longer durations. You would get better results running 4iu a day for twice as long as 8iu a day. The GH is not going to make you lose muscle itself, that is all going to come down to your diet and your lifting
. If your protein is high and calories aren't too far below maintenance you probably won't lose any muscle (or not enough that you could ever notice)
What kind of GH are you using and are you having any sides?