The use of testosterone is going to suppress your natural testosterone production. The rate and/or speed of this suppression is going to be dependent on the dose and the individual response. Although significant suppression will occur, if you have low testosterone it's not like you were producing enough to begin with. However, things like HCG will help keep what natural production you do have going. Is the use of HCG alone enough to give the individual the boost he needs? Sometimes, but more often it's not. Moreover, some men (unfortunately) do not respond well to HCG. I'm not referring to a poor physical reaction but one that produces no reaction. HCG simply doesn't work for some men.