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.
Dutasteride was patented in 1996  and was first described in the scientific literature in 1997.  It was approved by the FDA for the treatment of BPH in November 2001 and was introduced into the United States market the following year under the brand name Avodart.  Dutasteride has subsequently been introduced in many other countries, including throughout Europe and South America .  The patent protection of dutasteride expired in November 2015 and the drug has since become available in the United States in a variety of low-cost generic formulations .