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 doctors could not find any apparent cause for this rare problem other than that the subject used androgenic steroids. It was noted that some androgenic agents cause blood platelets and other coagulation factors to become more easily activated, and this may lead to dangerous clots that can plug up the arteries and veins that bring blood to and from various areas of the body. However, considering the million Americans who have or are currently using steroids, one suspects that far more case studies like this would have been reported, although the causes of many incidents may have been misdiagnosed.