Generally, testosterone therapy (HRT) does not result in significant testicular shrinkage, especially the topicals (Androgel, Testim, compounding). However, all testosterone therapy will tend to shut off the feedback cycle that occurs from the hypothalamus/pituitary to the testes to one degree or another. Essentially, the body says, "Oh! I've got plenty of plasma testosterone" and, therefore, does not pump out as much leutinizing hormone. (The feedback is actually based on estradiol interesting enough, but estradiol rises with increasing testosterone due to aromatization.) Of course, this is why hormone replacement therapy will almost always negatively affect male fertility. Again, though, testicular shrinkage should be minimal if dosed correctly. So based on the amount of testosterone you are using for HRT, HCG may not be needed.
GD