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.
Drugs During Pregnancy and Lactation, 3rd Edition is a quick and reliable reference for all those working in disciplines related to fertility, pregnancy, lactation, child health and human genetics who prescribe or deliver medicinal products, and to those who evaluate health and safety risks. Each chapter contains twofold information regarding drugs that are appropriate for prescription during pregnancy and an assessment of the risk of a drug when exposure during pregnancy has already occurred. Thoroughly updated with current regulations, references to the latest pharmacological data, and new medicinal products, this edition is a comprehensive resource covering latest knowledge and findings related to drugs during lactation and pregnancy.