How do you think DIY HRT works? Yes, sometimes people order actual manufacturer-made medications sold by overseas pharmacies. But that's not what people are talking about when they say homebrew hrt. Quite a lot of homebrew trans HRT is literally made in basement labs.

Most homebrew HRT is made by people in unlicensed compounding pharmacies. These community labs don't actually synthesize the active ingredients chemically. Rather, providers will order the raw active ingredients - such as estradiol enanthate powder - from overseas suppliers, usually Chinese companies that don't ask too many questions. They'll get the raw powder and then compound their own injection vials from it. This can be done safely in a garage or basement lab, if the right equipment is used. But make no mistake, a substantial portion of the trans community is currently getting by with HRT compounded in labs built in private homes. The people who do this tend to be trans themselves and usually not in it for the money. The quality is usually pretty good, as the providers tend to do it more as a community service project than a for-profit business. There's less incentive to cut corners if you're not actually trying to make a profit.