Testosterone replacement therapy can be administered via injections (using esters like cypionate, enanthate, decanoate, undecanoate) or topical application, with injections often preferred due to variability and absorption issues with topicals, especially for individuals with low SHBG.

“There's a lot of ways to get around this. So when you're doing testosterone replacement, if you're someone that needs it, you can have different types of esters, or you could do topical testosterone. So the Ester is basically something that's attached to increase the biological half-life. The most common ones are cypionate, enanthate, there's also a very short-acting propionate, which has almost no clinical relevance. And there's also very long-acting ones, decanoate, and undecanoate, and different mixtures of all those. So if you're someone who has a very, very low SHBG, you're going to have trouble of regulating your serum testosterone in the long run. If you do it topically, then the testosterone is absorbed, hopefully bound to SHBG, and then a lot of times you reapply twice daily or once daily, but you have lots of variations. So for most people, especially for people who can't absorb it well, that's not going to be a great option. So injections would be preferred. Most people end up injecting, because they have either side effects from too high, too low, or just too much of a varied dose when they do topical.