Testosterone injections and gel

Masculinizing HRT is commonly a testosterone monotherapy. The process is the same as in estrogen monotherapy for transfem people: adding enough exogenous testosterone will naturally decrease the production of estrogens and progesterone from the ovaries, through the negative feedback mechanism first decreasing FSH and LH. The use of anti-estrogens medication is almost never necessary.

In most cases, the interruption of ovarian activity stops menstruations. Some people might experience a relatively heavy bleeding after the first testosterone intake.

Testosterone is most commonly administered via injections, and mainly Intramuscular injections. In Sweden, the main product available through prescription is called Nebido, and consists of an injectable solution of testosterone undecanoate.

Injections allow for a longer time between each intake (this time will depend on the chosen testosterone ester), but it usually means less stable effects, with symptoms of underdosing when approaching the date of the next injection. This is particularly true for testosterone undecanoate, which allow for a very long time between injections (up to 3 months).

Other routes of administration exist: oral and transdermal. The oral route is rarely used, but transdermal gel is a good solution for people who wish to avoid injections. It is as efficient as injections, but necessitates a daily application, with a time to dry, and having to be careful for transfers when touching other people with the zones of application. Testosterone gels available in Sweden include Testavan, Testogel and Tostrex.

Injections: the different esters

Like estrogens, testosterone has been esterified in several forms. It is those esters that are used in injections, and - like estrogen esters - testosterone esters are prodrugs of testosterone, and hence considered as bioidentical testosterone.

• As we said above, the testosterone injection available in Sweden is Nebido and consists of testosterone undecanoate. Other existing esters, available in other countries, are testosterone cypionate, testosterone enanthate, and testosterone propionate.

• Testosterone undecanoate has a very long elimination half-life time, which, when administered via injection, allows for a very long time between each injection: from 2.5 to 3 months. This is much longer than with testosterone enanthate which necessitates an injection every two weeks (at best every month, must usually every 3 weeks).

However, as stated above, a smaller time between injections also means more stable levels and less effects of underdosing.