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.
I asked Catlin to check if Amazon has allowed the products back yet again. Sure enough, Amazon continues selling dangerous steroids and stimulants banned in sports and at least one drug regulated by the DEA, M-Drol , which contains the anabolic steroid methasterone. It is illegal to sell methasterone without a prescription and a DEA license. The DEA warned about methasterone in 2011, and this specific product has been recalled , yet it keeps making its way back onto Amazon. Amazon also trades in many compounds that are dangerous to the human body and banned by anti-doping agencies but aren’t yet illegal. One example is trenavar, marketed as TR3N , which is a “prohormone” that the body converts into another active compound. That compound is trenbolone, a DEA-controlled anabolic steroid. There’s nothing unusual about prodrugs as pharmaceuticals. We use many prescription prodrugs in daily medical practice, all regulated by the FDA, that become active only when processed inside the human body . That the DEA can’t easily regulate prodrugs of scheduled substances like trenbolone is simply an artifact of the outdated legislation that created the agency.
Prohormones are in a simple way to put it precursors or derivatives of steroidal hormones. While they often carry with them strong similarities they in many cases cannot be labeled anabolic steroids. However, in recent years many prohormones have been found to be so closely related to schedule III steroids they have been banned under the banner of illegal steroids by way of the Steroid Control Act of 2004. The Steroid Control Act of 2004 was an addition to the original Steroid Control Act of 1990 placing many other hormone or hormonal related drugs on the banned list classified as illegal steroids. Many of these prohormones come out year after year and remain legal for a time but generally each one is eventually pulled off the shelf; but year after year anabolic science produces new models ready for legal use; at least for a time.