Testosterone Injections
SOURCE: ELITE MENS GUIDE
Testosterone injections deliver testosterone deep into the muscle. The testosterone is then absorbed directly into the blood stream over time. The absorption period depends on the type of testosterone injected. Injections usually take place in the thighs, glutes or deltoid muscles.
The most common forms of injectable testosterone for
Testosterone Replacement Therapy (TRT) available in the US have long half-lives. These forms include testosterone enanthate (TE) and testosterone cypionate (TC). Due to their long half-lives, both TE and TC provide a sustained release of testosterone into the bloodstream for 2 to 3 weeks. As a result, testosterone injections need only be administered every week or every other week. The most commonly recommended dosing regimen for TRT is 100 to 200 mg every 2 weeks.
1-5 Approximately 30% of men treated for low testosterone use testosterone injections. [Approximately 65% of men use testosterone gel.]
6 (See EMG’s
T Levels for more information on testosterone and aging).
Testosterone Enanthate and Testosterone Cypionate
Testosterone enanthate and testosterone cypionate are modified forms of testosterone. Specifically, a carboxylic acid ester has been added to the 17-beta hydroxyl group. This attachment makes TE and TC less polar than free T. As a result, they have longer half-lives and are absorbed more slowly from the injection area. Once in the bloodstream, the ester is removed to yield free (active) T. Their slow-acting nature allows for less frequent testosterone injections.
Specifically, testosterone enanthate possesses a half-life of roughly 8-10 days.7 Testosterone cypionate possesses a half-life of roughly 10-12 days.7 [Half-lives depend on a person’s own rate of metabolism.] Therefore, it takes approximately 8 to 10 days for the body to metabolize and clear half the concentration of the testosterone enanthate following an injection. As a result, users may go two weeks between injections. Since injectable testosterone has been around for so long, generic versions of these medications are available. Compared to newer branded forms, this form is relatively inexpensive.
Two Potential Down Sides of TE and TC Testosterone Injections
Unfortunately, testosterone injections do not mimic physiologic dosing. As a result, T levels can fluctuate in the period between injections. Fluctuations in testosterone are not ideal. These fluctuations can affect mood, emotional stability, and sexual activity.2
Following an injection of testosterone enanthate or testosterone cypionate, T levels exceed normal physiological levels for the first 2 to 3 days. They then steadily decline to levels below physiological levels just prior to the next injection. The graphic below illustrates T levels following TE and TC injections. Shortening the interval between testosterone injections and lowering the dose can minimize this cyclical nature of highs and lows. Nevertheless, these peaks and troughs still exist. Fortunately, another testosterone ester, testosterone undecanoate, has been approved that maintains T levels in normal ranges.7-9
In addition to not mimicking physiologic dosing, injectable testosterone also show a stronger impact on raising red blood cell levels than transdermal options.
10-13 One of the more concerning potential side effects of TRT is an increase in red blood cells. Testosterone stimulates the production of red blood cells. In most cases the increase in red blood cells is small (2-5%) and within a safe range. However, for a considerable number of TRT users, testosterone injections produce red blood cell levels above safe levels over 50%. This increase in red blood cells causes your blood to become more viscous. Blood that is too viscous increases your risk of forming blood clots, which can subsequently lead to a heart attack and/or stroke. (See
Side Effects of Testosterone).
Aveed: A Newly Approved, Very-Slow Acting Injectable Testosterone
Recently, the US FDA approved injectable testosterone undecanoate (2014). Endo Pharmaceuticals will market it under the brand name Aveed. Testosterone undecanoate has actually been available under the brand name Nebido for over 10 years outside the US. Testosterone undecanoate is very slow acting. The drug provides a sustained release of testosterone into the bloodstream for up to 10 weeks.
In its Phase 3 Study, treatment with AVEED 750 mg maintained T levels in the normal range over 10 week dosing interval.6,14 The figure below illustrates T levels after the third injection. While testosterone undecanoate does not raise levels above normal, testosterone injections of TU still do not mimic physiologic dosing.
Pros of Testosterone Injections:
- Injectable testosterone is inexpensive if self-administered. The two most common forms (testosterone enanthate and testosterone cypionate) are both generic medications in the United States.
- Only need testosterone injections every two weeks (for testosterone cypionate and testosterone enanthate). A longer lasting version, testosterone undecanoate, is now available in the US. The FDA approved injectable testosterone undecanoate in 2014. Endo Pharmaceuticals will market it under the brand name Aveed. It will extend the period between injections to 10 weeks after an initial ramp-up period.
- Flexible dosing. Dosages can be changed with each injection, if necessary, to achieve optimal concentrations.
Cons of Testosterone Injections:
- T levels fluctuate between TE and TC testosterone injections. This results in more negative side effects than administration methods that provide more stable blood testosterone concentrations. Shortening the interval between injections can minimize this cyclical nature of highs and lows. It also can be achieved by lowering the dose. The longer lasting version of injectable testosterone, testosterone undecanoate, maintains T levels in normal ranges.
- Testosterone injections are more likely to cause an increased red blood cell count than other forms.
- Injection site pain is relatively common.
- Need to visit a physician for testosterone injections if unable to self-administer at home.
Suppliers
Both testosterone enanthate and testosterone cypionate are widely available in generic forms. Testosterone undecanoate is marketed under the brand name Aveed by Endo Pharmaceuticals.
Injection Information
For injection information, the University of Michigan provides a detailed primer on How to give a Testosterone Intramuscular (IM) Injection. Also, ask your physician to explain and demonstrate the technique.
Common Esters Available for Testosterone Injections
Below is a discussion of common testosterone esters. The primary difference between esters is the rate at which testosterone enters the bloodstream following an injection. A slower release means fewer testosterone injections per year. Testosterone propionate is a fast-acting ester rarely used in TRT. Testosterone enanthate and testosterone cypionate are slow-acting injectable forms. They have been the predominant form used for TRT. Testosterone undecanoate is a newly approved form that is very slow acting.
Testosterone Cypionate
Testosterone cypionate is a slow-acting injectable form of the androgen testosterone. Following deep intramuscular injection, the drug provides a sustained release of testosterone into the bloodstream for 2 to 3 weeks.14 Testosterone cypionate possesses a half-life of 10-12 days. The most commonly recommended dosing regimen for TRT is 100 mg to 200 mg every 2 weeks. Typically, 26 injections are required per year.
Testosterone Enanthate
Similar to testosterone cypionate, testosterone enanthate is a slow-acting injectable form of the androgen testosterone. Following deep intramuscular injection, the drug provides a sustained release of testosterone into the bloodstream for 2 to 3 weeks.14 Testosterone enanthate possesses a half-life of 8-10 days. The most commonly recommended dosing regimen for TRT is 100 mg to 200 mg every 2 weeks. Typically, 26 injections are required per year.
Testosterone Propionate
In comparison to testosterone enanthate and testosterone cypionate, testosterone propionate is a faster-acting form of the androgen testosterone. Testosterone propionate possesses a half-life of roughly 1-2 days. Therefore, testosterone propionate does not provide a sustained release. Due to this short half-life, it must be injected every other or every third day. As a result, it is rarely used for TRT.
Testosterone Undecanoate
Testosterone undecanoate is very slow-acting injectable form of the androgen testosterone. Following deep intramuscular injection, the drug provides a sustained release of testosterone into the bloodstream for up to 10 weeks. Testosterone undecanoate has been available under the brand name Nebido for over 10 years in more than 80 countries. However, it was not approved for use in the US.
Recently, however, the US FDA approved injectable testosterone undecanoate (2014). Endo Pharmaceuticals will market it under the brand name Aveed. Aveed is a depot formulation of testosterone undecanoate (TU) indicated for long-term TRT. Testosterone injections of 750 mg Aveed maintain normal levels between 300 and 1000 ng/dL for up to 10 weeks. Following baseline administration of 750 mg, a second 750 mg dose is given at 4 weeks followed by 750 mg every 10 weeks thereafter.
Due to the very slow-acting nature, Aveed will offer men with low testosterone a more convenient treatment option than currently available preparations. The injection interval for TU, after the loading dose, is 10 weeks. This equates to approximately 5 injections per year. In comparison, testosterone gels require daily dosing and testosterone enanthate and testosterone cypionate require injections every other week (26 injections per year).
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