Testosterone can be administered parenterally , but it has more irregular prolonged absorption time and greater activity in muscle in enanthate , undecanoate , or cypionate ester form. These derivatives are hydrolyzed to release free testosterone at the site of injection; absorption rate (and thus injection schedule) varies among different esters, but medical injections are normally done anywhere between semi-weekly to once every 12 weeks. A more frequent schedule may be desirable in order to maintain a more constant level of hormone in the system.  Injectable steroids are typically administered into the muscle, not into the vein, to avoid sudden changes in the amount of the drug in the bloodstream. In addition, because estered testosterone is dissolved in oil, intravenous injection has the potential to cause a dangerous embolism (clot) in the bloodstream.
Without the C17-aa nature, most oral steroid pills would be useless, but the obvious question is while they carry a toxic nature, how toxic is it? Different steroid pills carry varying levels of toxicity, for example, Halotestin is the most toxic of all C17-aa steroids, while Anavar is very mild. Of course, total dosing and duration of use will play a role, but on a per pill basis, most steroid pills are not as damaging to the liver as excessive alcohol consumption, and not nearly as toxic as many over the counter medications. Even so, unlike most over the counter medications, because steroid pills are taken every day when they are being used this presents a higher level of toxicity to the liver. When you supplement with oral steroids, your liver enzyme levels will increase, and this is assured. However, for the healthy adult male who does not add any additional stress to his liver, who lives a healthy lifestyle and supplements responsibly, once use is discontinued his enzyme levels will return to normal. The liver has remarkable rejuvenating capabilities, and with responsible use, permanent damage can in most all cases be avoided.