Androgenic Anabolic Steroids (AAS) are controlled substances, prescription only in the USA, and a felony to posses without a script. In some countries it is a misdemeanor, in others only illegal to sell without a license, and in some they are perfectly legal.
These are substances that either are testosterone, or variations of it. They will not shrink a penis, at all. If anything you will have a larger harder erections while using them. Frequent ones too, like during puberty. The only exceptions being 19-nor based steroids (keep in mind there are many kinds of steroids), that only have a weak affinity for the androgen receptor, and if used without testosterone, the guy will likely not be able to get it up. Often called Deca-Di*k, named after the 19-nor steroid Nandrolone Deconate.
Now most AAS will cause testicular atrophy, that is some shrinking of the testes due to the body not using them to produce testosterone while AAS are being used. The body has a regulatory system used for keeping sex hormones in check, and when elevated the body will shut down its own production, and the testes will shrink. Its not a big difference, not one I ever noticed, its not like they turn into peas. Also, once the AAS use stops they return to their normal size. In most cases it’s a temporary issue that can actually take months to show up in the first place, and often will only start to show up near the end of a 16 week cycle.
As to breast tissue growth, gynecomastia, that is what aromitase inhibitors are used. The aromitase enzyme converts androgens into estrogens, in particularly Estradiol. Take too high a dose of AAS and if too much converts you better have and AI on hand or you will get puffy sensitive nipples, retain water, and you will cry from sad movies.
Anyway, my suggestion is to stay away from AAS unless you have a medical need.
