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.
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The use of anabolic steroids will suppress natural testosterone. The rate of suppression is dependent on the steroid in question, but in the case of Oxymetholone it is enough to warrant the use of exogenous testosterone. This will actually hold true with most anabolic steroids. Those who supplement with Anadrol and forgo exogenous testosterone therapy will fall into a low testosterone condition. Not only is this a condition that comes with numerous bothersome symptoms, it is an extremely unhealthy state. The form of testosterone you choose when using Anadrol is of no consequence, however, you should ensure you are applying enough to provide what the body needs.
Once the use of Anadrol and all anabolic steroids has come to an end and all the exogenous hormones have cleared your system natural testosterone production will begin again. This is assuming there was no prior existing low level state. It also assumes no damage was done to the HPTA during supplementation due to improper practices. While natural testosterone production will begin again on its own, it will not be fast. It is generally recommended that the individual begin a Post Cycle Therapy (PCT) treatment plan following anabolic steroid use . This will encourage natural testosterone production and speed the healing process up. It will not automatically return you to your previous natural high level on its own; that will take some time. However, it will ensure you have enough testosterone in your body to function properly while your levels continue to naturally rise.