Lauren Schlanger, MD, is a board-certified primary care physician with a focus on women's and trans health.

Transgender men and other transmasculine individuals may use testosterone to masculinize their bodies in order to align their bodies with their gender identity.

Unlike transfeminine people who need to use a testosterone blocker in order for gender-affirming hormone therapy to be effective, there is no need to block the production of estrogen when taking testosterone. Testosterone is a more biologically effective hormone, and it will induce changes when taken on its own.

When people take testosterone to affirm their gender, it can lead to a number of permanent, irreversible changes in the body. (This is in contrast with puberty blockers, which are reversible.)

Desirable physical changes that can be caused by testosterone include:

Transgender men and transmasculine individuals who take testosterone for gender dysphoria also report declines in dysphoria, depression, and anxiety. This is because the treatment helps align their bodies to fit their identities and makes them feel more like themselves.

There are aspects of gender affirmation that testosterone treatment cannot manage on its own, however. If an individual has gone through puberty and grown breasts, testosterone may somewhat shrink the breast tissue, but not remove the breasts entirely.

Further, testosterone cannot make someone grow taller if their bones have already matured from early estrogen exposure.

Different types of testosterone can be administered in different ways. There are advantages and disadvantages to each of these options.

In addition to different formulations by which testosterone can be administered, there are also different types of testosterone, referred to as testosterone esters. These include testosterone cypionate, testosterone enanthate, and testosterone undecanoate.

Testosterone undecanoate has only recently become available in the United States in an injected formulation (brand name Aveed) and oral formulations (Kyzatrex, Jatenzo, and Tlando). All carry black box warnings advising about the risk of malignant hypertension and, as such, are used with extreme caution under strict medical supervision.

There is limited information comparing the safety and efficacy of these different testosterone esters, and they are thought to be largely interchangeable. In general, most providers prescribe the types that come in an appropriate format for the patient.

Prescription choices may also be limited by the availability of certain types of testosterone. There can also be substantial cost differences, and not all formulations are covered by all insurers.

Different testosterone formulations have different methods of delivery. Injections are the most familiar methods, but advances in therapy have led to topical and oral formulations as well.

Testosterone can be injected into the muscle (intramuscular or IM injection). Intramuscular injections have historically been the most easily available, but can be more painful than subcutaneous (under the skin) injections.

In addition, they may need to be administered by a medical provider or family member. Intramuscular testosterone injections are commonly used every one to two weeks.

Testosterone can also be injected under the skin (subcutaneous or sub-q injection). Subcutaneous injections are easier for people to give themselves, but they may not be a good option for those with needle anxiety.

However, they are less painful and easier to manage, due to less frequent medical visits, and are only used every one to two weeks.

This is a way to deliver long-lasting pellets of testosterone under the skin, reducing the frequency of treatment to once every three to six months. Sold under the brand name Testopel, the subcutaneous pellets allow for easy, long-term dosing without the need for repeated doctor visits or self-injection.

However, the dose is fixed after implantation. This can be a problem if dose changes are needed to either raise or lower the amount of testosterone in the body.

Testosterone can be delivered topically through gels, creams, and patches. Testosterone gels and creams are easy to use. However, they generally must be used daily.

In addition, it is important to keep other people from touching the gel or skin after gel application. Otherwise, they may also get a dose of testosterone.

There is a risk for a local skin reaction or rash with topical testosterone. This includes testosterone patches, which can also be difficult to find and/or to get covered by insurance.

Oral testosterone formulations were a less common option in the past and ones that were associated with liver toxicity. However, the release of the oral capsules Kyzatrex, Jatenzo, and Tlando allayed those fears significantly. Although not formally indicated for testosterone replacement therapy in transgender men, it has become an increasingly popular option for some.

Approved for use in 2019, Jatenzo is taken twice daily by mouth. The treatment is monitored closely to avoid side effects and adjust the daily dose based on blood testosterone levels.

Testosterone treatment is not without side effects. Some are mild to acceptable. Others may become intolerable and require the adjustment (or even discontinuation) of treatment.

Possible side effects of testosterone replacement therapy in transgender men include:

It is unclear whether these risks in transgender men are any higher than in cisgender men. However, they are known to be higher than in cisgender women and appear to be higher in transgender women as well.

Testosterone is generally considered to be a safe and effective way for transmasculine people to affirm their gender identity. However, it’s not something that should be undertaken without adequate information and consideration.

In particular, it’s important for transgender men and non-binary people considering testosterone to think about their fertility prior to starting testosterone. It is much easier to undergo any desired fertility preservation before hormonal gender affirmation than after.

Although testosterone is somewhat effective at stopping menstruation, it should not be used as the sole form of contraception for transmasculine people who have penetrative sex with partners with penises. Although it may not be common, it is possible to get pregnant if you don’t have periods.

Therefore, those who are at risk of unintended pregnancy should consider using additional forms of contraception, such as condoms or an intrauterine device (IUD).

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By Elizabeth Boskey, PhD Elizabeth Boskey, PhD, MPH, CHES, is a social worker, adjunct lecturer, and expert writer in the field of sexually transmitted diseases.

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