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.
The most serious complication of anabolic steroid use is the development of hepatic tumors, either adenoma or hepatocellular carcinoma. The hepatic tumors arise in patients on long term androgenic steroids, usually during therapy of aplastic anemia or hypogonadism, but occasionally in athletes or body builders using anabolic steroids illicitly. Tumors are typically found after 5 to 15 years of use, but onset within 2 years of starting therapy with testerosterone esters has been described. Many of the case reports have occurred in patients with other risk factors for cancer, such as Fanconi?s syndrome, iron overload or chronic hepatitis C (from blood transfusions). However, hepatic adenomas and hepatocellular carcinoma have also been described in patients taking androgenic steroids who have no other evidence of liver disease and normal histology in the nontumor parts of the liver. The pathology of the tumors is usually hepatic adenoma or ?well differentiated? hepatocellular carcinoma or hepatic adenoma with areas of malignant transformation. Rare instances of cholangiocarcinoma and angiosarcoma have also been described in patients on long term androgenic steroids. Clinical presentation is generally with right upper quadrant discomfort and a hepatic mass found clinically or on imaging studies. Routine liver tests are often normal unless there is extensive spread or rupture or an accompanying liver disease. Alphafetoprotein levels are usually normal. There is often (but not always) spontaneous regression in the tumor when the anabolic steroids are stopped. Hepatocellular carcinoma arising during anabolic steroid therapy is believed to have a better prognosis than that related to cirrhosis or chronic hepatitis B and C; however, deaths from hepatic rupture or tumor spread and metastasis have been reported in patients with anabolic steroid related hepatocellular carcinoma without cirrhosis.