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.
Then there are the cardiovascular problems. Because of the way they affect heart cells, anabolic steroids can cause chronic high blood pressure, as well as enlargement of the heart. Your cholesterol levels also get thrown out of balance, since your steroid-saturated body is producing more LDL cholesterol and less HDL cholesterol , which is the opposite of what the American Heart Association recommends. The hormonal effects of steroid use also increase your risk of prostate cancer (if you’re male) and can cause kidney and liver damage.