Physical changes from hormone therapy

Gender-affirming hormone therapy (GAHT) changes the body profoundly and gradually. For many trans people, it represents the first concrete step in medical transition: the effects are real, documented by decades of research, and follow relatively predictable timelines. However, every body responds uniquely, and knowing in advance what to expect helps one approach the process with awareness.

This article reviews the physical changes of estrogen therapy and testosterone therapy, with detailed timelines based on the Endocrine Society guidelines (2017) and the WPATH Standards of Care Version 8 (2022) [1][2].

How hormone therapy works

Hormone therapy brings estrogen or testosterone levels into the physiological range of the affirmed gender. For trans women, this means administering estrogen (often estradiol) combined with an anti-androgen. For trans men, testosterone is administered via injections, gel, or patches. The goal is not to create something artificial: the same changes as puberty are induced, but in an adult body.

The Endocrine Society guidelines recommend monitoring every 3 months in the first year, then 1-2 times per year, to verify that hormone levels are in the correct range and to identify any side effects promptly [1].

Effects of estrogen therapy (trans women)

Estrogen therapy, typically combined with an anti-androgen, produces a series of changes that mirror female puberty. Here is what to expect and when.

Breast development

Breast development is one of the most anticipated changes. The first sign is the appearance of a breast bud under the areola, usually between 3 and 6 months from the start of therapy. According to the multicenter study by de Blok et al. (2018), which followed 229 trans women for one year, most breast development occurs in the first 6 months, with an average increase in the breast-to-chest difference of 1.8 cm in the first 3 months and 1.3 cm in the following 3 months [3].

Results are highly variable: after one year, approximately half of the participants had not reached an AAA cup, and only 3.6% exceeded an A cup [3]. No clinical or laboratory parameter (age, weight, estradiol level, route of administration) proved predictive of breast development. A 3-year follow-up study (de Blok et al., 2021) confirmed that development continues, albeit slowly, beyond the first year [14].

Breast development timeline:

• 1-3 months: nipple sensitivity and tenderness
• 3-6 months: appearance of the breast bud, beginning of development
• 6-12 months: gradual volume increase, growth slows
• 1-3 years: continued development, more defined shape
• 2-5 years: maximum result reached

Fat redistribution

Estrogen changes how the body accumulates fat. The multicenter study by Klaver et al. (2018) documented a significant increase in fat on the hips, thighs, and buttocks, with a simultaneous reduction in abdominal fat [4]. This change contributes to a more rounded silhouette and a more feminine overall appearance.

Fat redistribution timeline:

• 3-6 months: first measurable changes
• 6-12 months: visible redistribution
• 2-5 years: maximum effect

This change is reversible: if therapy is discontinued, fat tends to redistribute according to the previous pattern.

Skin and body hair

The skin becomes thinner, softer, and less oily. Sebum production decreases, pores shrink, and the skin becomes less prone to acne. Body hair is reduced and becomes finer, but does not disappear entirely: electrolysis or laser remain necessary for the beard and areas with terminal hair already developed [12].

Skin change timeline:

• 1-3 months: less oily skin, first changes in texture
• 3-6 months: visible reduction in body hair
• 6-12 months: noticeably softer skin
• 1-2 years: progressive reduction of hair, which becomes thinner

Androgenetic hair loss may slow or stop, but hair already lost does not regrow. In some cases, a slight improvement in the density of existing hair is observed.

Muscle mass and strength

Estrogen, combined with testosterone suppression, causes a reduction in muscle mass and strength. According to a systematic review (Harper et al., 2021), lean mass decreases by approximately 5% after 12 months and continues to decline beyond 3 years of therapy [9]. Grip strength decreases significantly, although it may not completely reach typical cisgender female levels.

Muscle change timeline:

• 3-6 months: first measurable decreases in strength
• 6-12 months: visible reduction in muscle mass
• 1-3 years: progressive decline, gradual stabilization

This change is reversible if therapy is discontinued.

Sexual and reproductive function

Estrogen therapy significantly modifies sexual function. A reduction in spontaneous erections, a decrease in ejaculate volume, and a possible reduction in libido are observed. The testicles progressively atrophy. Wierckx et al. (2014) found that approximately two-thirds of trans women report a decrease in sexual desire after therapy [8].

Sexual change timeline:

• 1-3 months: reduction in spontaneous erections, decrease in libido
• 3-6 months: reduction in ejaculatory volume, changes in erectile function
• 6-12 months: possible infertility (variable)
• 2-3 years: significant testicular atrophy

Fertility is compromised, often irreversibly with prolonged treatment. The guidelines recommend discussing sperm cryopreservation before starting therapy [1].

Voice changes

Estrogen does not change the voice in trans women. The vocal deepening that occurred during male puberty is irreversible. To modify the voice, speech therapy training or, in some cases, vocal cord surgery is necessary.

Effects of testosterone therapy (trans men)

Testosterone produces changes that are often more rapid and visible than those of estrogen. Many effects are permanent, making the decision to begin therapy particularly significant.

Voice

Voice deepening is one of the most desired and earliest changes. A study published in Scientific Reports (Azul et al., 2021) demonstrated that the fundamental frequency of speech drops from approximately 183 Hz to 134 Hz, and that after approximately 37 weeks, listeners identify the voice as male [7]. The process begins in the first months and is generally complete within 1-2 years.

Voice change timeline:

• 1-3 months: sensation of hoarseness, the voice begins to “crack”
• 3-6 months: progressive and noticeable deepening
• 6-12 months: significant deepening, voice recognized as male
• 1-2 years: stabilization in the definitive register

This change is irreversible. Even if therapy is discontinued, the voice does not return to the previous register.

Beard growth and body hair

Testosterone stimulates the growth of terminal hair on the face and body. Wierckx et al. (2014) documented a progressive increase: the Ferriman-Gallwey score (a hair growth measurement scale) goes from a median value of 0.5 to 12 after 12 months of therapy [6]. After several years of treatment, body hair reaches levels comparable to those of cisgender men.

Hair growth timeline:

• 2-4 months: first hairs on the upper lip and chin
• 6-12 months: early-stage beard, increase in body hair
• 1-2 years: fuller beard, though with possible sparse areas
• 2-5 years: full beard development (highly variable)

Beard growth is irreversible. As with cisgender men, genetics plays a determining role: not everyone develops a full beard.

Fat redistribution

Testosterone shifts fat accumulation from the hips and thighs to the abdomen, producing a more android body profile. The study by Klaver et al. (2018) confirmed that after one year of therapy, fat distribution in trans men approaches that of cisgender men significantly [4].

Fat redistribution timeline:

• 3-6 months: first changes in distribution
• 6-12 months: visibly more masculine body profile
• 2-5 years: maximum effect

This change is reversible if therapy is discontinued.

Muscle mass and strength

Testosterone increases lean mass and strength. Irwig (2017) documented a significant increase in muscle mass and a reduction in fat mass in trans men [5]. These changes are among the most rapid and appreciated.

Muscle change timeline:

• 1-3 months: increase in energy and perceived strength
• 6-12 months: measurable increase in muscle mass
• 1-3 years: body composition approaching that of cisgender men

This change is partially reversible: muscle mass decreases if therapy is discontinued.

Skin and acne

Testosterone increases sebum production, making the skin oilier. Acne is a common side effect, peaking around 6 months and then tending to improve. Wierckx et al. (2014) observed that after long-term treatment, 94% of participants had absent or mild acne [6].

Androgenetic hair loss may occur in genetically predisposed individuals: after years of treatment, approximately one-third of trans men show some degree of frontotemporal thinning.

Skin change timeline:

• 1-3 months: oilier skin, first pimples
• 3-6 months: peak acne
• 6-12 months: acne improving, skin stabilized
• Subsequent years: possible onset of androgenetic hair loss

Menstrual cycle and reproductive function

Cessation of menstruation is one of the earliest and most desired effects. In many cases, periods stop within the first 2-6 months [5]. Testosterone causes endometrial atrophy and suppresses egg production.

Timeline:

• 1-3 months: irregular cycle, reduced flow
• 2-6 months: complete cessation in most cases
• 6-12 months: cessation in nearly all cases

Fertility is compromised, but not always permanently: pregnancies after discontinuation of therapy are documented. The guidelines recommend discussing oocyte cryopreservation before starting treatment [1].

Clitoral growth

Testosterone causes an increase in clitoral size (clitoromegaly), which can reach 1-3 cm on average [5]. This change begins in the first months and reaches its maximum in 1-2 years. It is considered irreversible or only partially reversible.

Timeline:

• 1-3 months: increased sensitivity, first changes
• 3-6 months: visible growth
• 1-2 years: maximum dimensions reached

Libido and sexuality

Testosterone significantly increases libido in most trans men. Wierckx et al. (2014) documented that approximately two-thirds of trans men report an increase in sexual desire [8]. This change is among the most rapid, often noticeable within the first few weeks.

Emotional and psychological changes

Hormone therapy does not only change the body: it also influences mood and psychological well-being. Colizzi et al. (2014) demonstrated a significant reduction in anxiety and depression levels after one year of hormone therapy, regardless of the type of treatment [11].

Those taking estrogen often report greater emotional reactivity: emotions are perceived more intensely, crying becomes more frequent. Those taking testosterone may experience an emotional range perceived as more “flat” or controlled, with a greater tendency toward irritability in the first months, which then stabilizes.

These emotional changes are not purely psychological: sex hormones directly influence brain receptors involved in mood regulation. It is important to distinguish the physiological effects of hormones from the psychological relief linked to the alignment between body and identity, which independently contributes to improved well-being [13].

Reversible or irreversible: the complete picture

Not all changes from hormone therapy are permanent. This distinction is essential for anyone considering whether to begin treatment.

Reversible changes (return if therapy is discontinued)

• Body fat redistribution
• Muscle mass and strength
• Skin quality (sebum, softness)
• Libido and sexual function
• Hemoglobin levels
• Cessation of menstruation (with testosterone)

Irreversible or partially irreversible changes

• Breast development (with estrogen): does not regress without surgery
• Voice deepening (with testosterone): permanent
• Beard growth (with testosterone): permanent
• Clitoral growth (with testosterone): largely permanent
• Androgenetic hair loss: does not fully reverse

This distinction is drawn from the Endocrine Society guidelines (2017) and the WPATH SOC 8 (2022) [1][2]. The UCSF guidelines (2016) offer a particularly clear summary of this information for those who wish to explore further [12].

Individual variability

A point that the scientific literature consistently emphasizes: results vary enormously from person to person. The study by de Blok et al. (2018) found no parameter capable of predicting breast development [3]. Genetics, age at the start of therapy, BMI, and other factors influence the final result in ways that are not yet fully understood.

This means that comparing one’s own results with those of other people is of limited use. The timelines reported in this article are statistical averages: some people will see faster changes, others slower. The important thing is to maintain realistic expectations and an open dialogue with one’s endocrinologist.

Medical monitoring and blood tests

Hormone therapy requires regular monitoring. The Endocrine Society guidelines (2017) recommend [1]:

• Every 3 months in the first year: estradiol and testosterone levels, complete blood count, liver function, lipid profile
• Every 6-12 months thereafter: same tests, with periodic addition of bone density screening (especially for trans women)
• Specific checks for trans women: prolactin monitoring (the risk of prolactinoma is very low but should be monitored), thromboembolic risk screening
• Specific checks for trans men: hematocrit (testosterone increases red blood cell production, and an excessively high hematocrit increases cardiovascular risk), lipid profile

The study by Wiepjes et al. (2017) confirmed that bone mineral density increases in both trans women and trans men after one year of therapy, a reassuring finding for long-term skeletal health [10]. Long-term monitoring nevertheless remains recommended [13].

Conclusion

Hormone therapy produces real, documented, and predictable changes, but requires patience. Like a second puberty, the process unfolds over years, not weeks. Knowing the timeline and nature of the changes (which are reversible and which are not) helps one make informed decisions and manage expectations.

Scientific research continues to provide increasingly detailed data on the long-term effects of hormone therapy [13]. What we know with certainty is that, under adequate medical supervision, hormone therapy is safe, effective, and associated with a significant improvement in quality of life [11].