A substance can be legal but may be banned in certain circumstances. For instance, an insurance company may test an insurance applicant for nicotine to verify the person's assertion that he or she is not currently using tobacco. In the case of prescription medications, the high addictive potential for certain medications makes drug testing important. In the case of some athletes, many of the prohibited substances are legal but have the potential to affect the athlete's performance. Athletes must exercise caution in their choices of medications as they are ultimately responsible for any substances detected in their bodies.
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.