# Transgender Endocrinology ## Terminology and Overview ### Key Definitions The field of transgender endocrinology centers on the hormonal management of individuals whose gender identity differs from their sex assigned at birth. A transgender woman (male-to-female/MTF/transfeminine) was assigned male at birth, identifies as female, and seeks feminizing therapy. A transgender man (female-to-male/FTM/transmasculine) was assigned female at birth, identifies as male, and seeks masculinizing therapy. Non-binary or gender diverse individuals have a gender identity outside the traditional male/female binary and may seek partial hormonal therapy or none at all. Gender dysphoria describes the clinically significant distress arising from the incongruence between gender identity and sex assigned at birth. Gender-affirming hormone therapy (GAHT) is the term for hormone treatment designed to develop physical characteristics consistent with the individual's gender identity. ### Prevalence An estimated 0.3-0.6% of adults identify as transgender, with increasing prevalence recognized as broader social acceptance and awareness expand. Adolescent referrals to gender clinics have increased significantly over the past decade across many countries. ### Role of the Endocrinologist The endocrinologist's role in transgender care encompasses hormone prescribing and monitoring, screening for contraindications and risk mitigation, long-term health surveillance (cardiovascular, bone, metabolic, and cancer screening), and coordination with mental health, primary care, and surgical teams. The informed consent model, in which adults access hormones directly without mandatory mental health evaluation, is increasingly adopted in clinical practice. ## Pre-Treatment Evaluation ### Assessment Prior to initiating GAHT, persistent gender dysphoria (per DSM-5 criteria) or gender incongruence (ICD-11) should be confirmed. A mental health assessment is strongly recommended but, under the informed consent model, is not always required as a gatekeeper. Evaluation should include assessment for comorbid depression, anxiety, and suicidality, which are significantly higher in transgender individuals and are reduced by GAHT. The medical history and physical exam should address cardiovascular risk factors, history of venous thromboembolism, liver disease, hormone-sensitive cancers, and reproductive history. Baseline laboratory testing includes CBC, metabolic panel, lipid panel, fasting glucose or HbA1c, liver function, baseline sex hormones (testosterone, estradiol), and prolactin (particularly for transfeminine patients). Karyotype may be considered in adolescents. ### Fertility Counseling (Essential Before Starting GAHT) Fertility counseling is essential before initiating GAHT because hormonal therapy impairs fertility to a variable degree that is potentially irreversible with prolonged use. Transfeminine individuals should be offered sperm cryopreservation before starting estrogen. Transmasculine individuals should be offered oocyte or embryo cryopreservation before starting testosterone, with ovarian tissue cryopreservation as an experimental option. Some transgender individuals may wish to use their native reproductive capacity in the future, and this possibility must be discussed explicitly. Importantly, testosterone does not provide reliable contraception, and pregnancy can occur even while on testosterone therapy. ## Feminizing Hormone Therapy (Transfeminine) ### Goals The goals of feminizing therapy include breast development, body fat redistribution to the hips and thighs, reduced body hair growth, softer skin, reduced muscle mass, testicular atrophy, and decreased libido (if desired). GAHT does not change voice (voice training is needed), skeletal structure, or height. The timeline for changes varies: breast development begins at 3-6 months with maximum effect at 2-3 years; body fat redistribution starts at 3-6 months; decreased body hair takes 6-12 months. ### Estrogen Therapy Estradiol (17-beta-estradiol) is the preferred estrogen, being bioidentical and available in multiple routes. Oral dosing at 2-6 mg daily starts low at 2 mg with titration; the hepatic first-pass effect increases VTE risk. Transdermal patches delivering 0.1-0.4 mg daily (100-400 mcg) avoid first-pass metabolism and carry lower VTE risk, making them preferred for patients over 40, smokers, those with VTE risk factors, obesity, or migraine with aura. Intramuscular or subcutaneous estradiol valerate or cypionate at 2-10 mg every 1-2 weeks or 1-5 mg weekly provides stable levels and is widely used. Sublingual dosing at 1-4 mg twice daily offers rapid absorption with partial bypass of first-pass metabolism but has a short half-life. The target estradiol level is 100-200 pg/mL (physiologic female range), with levels above 200 pg/mL associated with increased VTE risk. Ethinyl estradiol is not recommended due to higher thrombogenic risk than 17-beta-estradiol, as documented in early transgender studies. Conjugated equine estrogen is also not recommended because of less predictable pharmacology and inability to monitor levels. ### Anti-Androgen Therapy | Anti-Androgen | Dose | Mechanism | Key Side Effects | Availability | |---|---|---|---|---| | Spironolactone | 100-300 mg daily | AR antagonist + weak 5-alpha-reductase inhibitor; modest T reduction | Hyperkalemia (monitor K+); menstrual irregularity | US (most common) | | Cyproterone acetate | 10-50 mg daily | Potent progestin + anti-androgen; significant T suppression | Meningioma (dose-dependent), hepatotoxicity, depression, prolactinoma | Outside US (not FDA-approved) | | GnRH agonists (leuprolide) | Variable | Complete gonadal suppression | Expensive; injection required | Worldwide | | Bicalutamide | 50 mg daily | Non-steroidal AR antagonist (does not lower T) | Hepatotoxicity (monitor LFTs); growing use | Off-label | | 5-alpha-reductase inhibitors | Finasteride 1-5 mg daily | Blocks T → DHT conversion | Primarily adjunct for hair loss | US/worldwide | Spironolactone at 100-300 mg daily is the most commonly used anti-androgen in the US, functioning as an androgen receptor antagonist with weak 5-alpha-reductase inhibitor activity and modest testosterone reduction. Potassium monitoring is required due to hyperkalemia risk, especially with renal impairment or ACE inhibitor/ARB use. Cyproterone acetate at 10-50 mg daily is a potent progestin with anti-androgen properties widely used outside the US (not FDA-approved). It is effective but carries risks of meningioma (dose and duration-dependent), hepatotoxicity, depression, and prolactinoma; the lowest effective dose should be used. GnRH agonists (leuprolide, goserelin) provide complete gonadal suppression and are used in both adolescents for puberty suppression and adults; they are very effective with no metabolic side effects but are expensive and require injection. Bicalutamide at 50 mg daily is a non-steroidal anti-androgen that blocks the androgen receptor without lowering testosterone levels; its use is growing but hepatotoxicity risk requires LFT monitoring. 5-alpha-reductase inhibitors (finasteride, dutasteride) are used primarily for hair loss as an adjunct. The target testosterone level is below 50 ng/dL (ideally below 30 ng/dL). When estrogen alone sufficiently suppresses testosterone, the anti-androgen may be reduced or discontinued. ### Progesterone Micronized progesterone at 100-200 mg orally nightly is increasingly requested by transgender women, with reported benefits in breast development (Tanner stage progression), sleep, and mood. However, evidence is largely anecdotal, with formal randomized controlled trial data lacking. Risks include uncertain long-term breast cancer contribution and possible mood effects including depression. Current guidelines neither recommend nor prohibit its use, leaving the decision to shared decision-making between clinician and patient. A monitoring and timeline infographic for feminizing hormone therapy. Show a timeline from month 0 to 36 months with expected changes and their approximate onset and maximum effect. Include: breast development (onset 3-6 months, max 2-3 years), decreased body hair (onset 6-12 months, max 3+ years), body fat redistribution (onset 3-6 months, max 2-5 years), decreased testicular volume (onset 3-6 months, max 2-3 years), decreased muscle mass (onset 3-6 months, max 1-2 years), softer skin (onset 3-6 months), decreased libido (onset 1-3 months). On a parallel track, show monitoring schedule: estradiol and testosterone levels at 3 months then every 6-12 months, potassium if on spironolactone, prolactin annually, lipids annually, fasting glucose, liver function. Include target lab values: estradiol 100-200 pg/mL, testosterone <50 ng/dL. Use timeline infographic with color-coded tracks. ## Masculinizing Hormone Therapy (Transmasculine) ### Goals The goals of masculinizing therapy include voice deepening, facial and body hair growth, increased muscle mass, fat redistribution to the abdomen, clitoral growth, cessation of menses, acne, and male-pattern baldness (in those with genetic predisposition). GAHT does not change skeletal structure (if past puberty), height, or breast tissue (top surgery is needed for chest masculinization). Voice deepening begins at 3-12 months and is permanent; facial hair develops at 6-12 months with full beard growth taking 2-5 years; menses typically cease within 2-6 months. ### Testosterone Formulations Intramuscular testosterone cypionate or enanthate at 50-100 mg weekly or 100-200 mg every 2 weeks is the most commonly used formulation; weekly dosing is preferred for more stable levels. Subcutaneous testosterone cypionate at the same doses as IM is increasingly used, being less painful with equivalent pharmacokinetics. Testosterone undecanoate IM (Aveed) at 750 mg every 10 weeks after loading provides long-acting, stable levels but requires the REMS program. Topical gel at 50-100 mg daily provides steady levels with risk of transfer but is less commonly used in transmasculine patients. Transdermal patches at 2-6 mg daily are less preferred due to common skin irritation. The target testosterone level is 400-700 ng/dL (mid-normal male range), measured as trough levels for IM injections. ### Monitoring Testosterone should be checked at 3-6 months, then every 6-12 months, measured as trough (for IM) or random (for topical). Estradiol should suppress below 50 pg/mL; persistent elevation may indicate ongoing ovarian activity, warranting consideration of a GnRH agonist or increased testosterone dose. Hematocrit and hemoglobin monitoring is the most important safety parameter, performed every 3-6 months initially, then annually. If hematocrit exceeds 54%, dose reduction, phlebotomy, and evaluation for obstructive sleep apnea or dehydration are required. Lipid panel annually (testosterone may worsen LDL and decrease HDL) and liver function annually complete the monitoring schedule. ## Risks and Safety Considerations ### Feminizing Therapy Risks VTE and pulmonary embolism risk is increased 2-5 fold, with the highest risk associated with oral estrogen (particularly ethinyl estradiol) and the first 1-2 years of therapy. Mitigation strategies include using the transdermal route, avoiding smoking, and avoiding ethinyl estradiol. Cardiovascular risk data are mixed, with possible increased MI and stroke risk particularly in older transgender women or those with risk factors. Prolactinoma is rare but reported; baseline prolactin and periodic monitoring are recommended, with cyproterone acetate further increasing the risk. Breast cancer risk is low overall but present; screening follows natal female guidelines after 5 or more years of GAHT. Bone density is maintained or improved with estrogen; risk increases if estrogen is discontinued without testosterone. Fertility impairment is progressive, with testicular atrophy that may become irreversible after prolonged therapy. ### Masculinizing Therapy Risks Polycythemia is the most common risk, with hematocrit exceeding 54% in approximately 5-10% of patients. Cardiovascular risk remains unclear from observational data, with unfavorable lipid effects noted but long-term cardiovascular risk uncertain. Parenteral testosterone rarely causes hepatotoxicity (unlike oral methyltestosterone). Acne is common and can be severe. Male-pattern baldness develops in genetically predisposed individuals. Testosterone causes vaginal atrophy and cervical changes; Pap smear screening continues per guidelines if the cervix is present, and testosterone is not reliable contraception. Bone density is maintained with testosterone; risk occurs if testosterone is discontinued without estrogen replacement. ## Adolescent Considerations ### Puberty Suppression (GnRH Agonists) GnRH agonist therapy for puberty suppression is fully reversible and suppresses endogenous puberty to allow time for gender identity exploration. It is initiated at Tanner stage 2-3 (the earliest signs of puberty) using agents such as leuprolide (Lupron) IM every 1-3 months or histrelin (Supprelin) implant annually. Monitoring includes LH, FSH, and sex steroids every 3-6 months and annual DXA scanning due to concerns about bone density accrual. GnRH agonists suppress bone mineral acquisition, making the addition of sex hormones at the appropriate age (typically 14-16 years) important for bone health. If puberty suppression is followed directly by cross-sex hormones without discontinuation, fertility may never develop, necessitating thorough counseling. Ongoing controversy exists regarding long-term neurodevelopmental effects, bone health, and optimal timing, with several European countries restricting puberty blocker use outside research settings. ### Cross-Sex Hormones in Adolescents Cross-sex hormones are typically initiated at age 14-16, though this varies by guideline and clinical judgment. Starting doses are lower than adult doses with gradual titration to mimic natural pubertal progression. A multidisciplinary team approach involving mental health, endocrinology, primary care, and family is recommended. ## Surgical Considerations for Endocrinologist ### Perioperative Hormone Management Estrogen was historically held before surgery due to VTE risk, but current practice is evolving. Many centers now continue estrogen with thromboprophylaxis, particularly transdermal preparations, using shared decision-making. Testosterone is generally continued perioperatively without significant thrombotic concern. VTE prophylaxis follows standard surgical risk assessment. ### Post-Gonadectomy Hormone Adjustment After orchiectomy in transfeminine patients, anti-androgen therapy is discontinued and the estrogen dose may be reduced, while ensuring adequate estrogen levels for bone health. After oophorectomy in transmasculine patients, testosterone is continued with possible dose adjustment, recognizing that without gonads, lifelong sex hormone replacement is essential to prevent osteoporosis and menopausal symptoms. ## Screening and Preventive Care ### Cancer Screening For breast cancer, transfeminine individuals should undergo screening mammography after 5 or more years of GAHT and age 50 or older (or per natal female guidelines); transmasculine individuals with remaining chest tissue (no top surgery) should continue natal female screening guidelines. Cervical cancer screening with Pap smears continues per natal female guidelines for transmasculine individuals with an intact cervix, noting that testosterone may cause atrophic changes that can be misinterpreted cytologically. Prostate cancer screening in transfeminine individuals follows natal male guidelines, recognizing that the prostate is present even after vaginoplasty and that PSA levels are very low on estrogen, rendering standard thresholds inapplicable. Ovarian and uterine cancer monitoring in transmasculine individuals with intact organs requires attention to abnormal bleeding, though no increased risk has been demonstrated. ### Bone Health DXA is recommended at baseline or at age 50 (earlier if risk factors exist). Reference range selection is debated: some use natal sex ranges while others recommend affirmed gender reference ranges after prolonged GAHT. The critical principle is ensuring adequate sex hormone levels at all times, as hormone discontinuation without replacement leads to rapid bone loss. ### Cardiovascular Risk Traditional risk factors (blood pressure, lipids, glucose, smoking, BMI) should be monitored. No specific cardiovascular screening guidelines exist for transgender patients beyond standard risk assessment, though increased vigilance is appropriate for transfeminine patients over 40 on oral estrogen. ## Key Clinical Pearls - Transdermal estradiol is preferred over oral in transfeminine patients over age 40, with VTE risk factors, or who smoke, due to significantly lower thrombotic risk (avoids hepatic first-pass effect) - Testosterone is NOT reliable contraception in transmasculine individuals; pregnancy can occur even with amenorrhea and testosterone therapy; discuss contraception if at risk - Fertility counseling and preservation options must be discussed BEFORE initiating GAHT, as effects on fertility may be irreversible, particularly with prolonged therapy - Target hormone levels are key to safe management: estradiol 100-200 pg/mL and testosterone <50 ng/dL for feminizing therapy; testosterone 400-700 ng/dL for masculinizing therapy; titrate doses to targets rather than using fixed doses - Hematocrit monitoring is the most critical safety parameter in masculinizing therapy; polycythemia (hematocrit >54%) requires dose reduction and evaluation; testosterone-induced polycythemia is the most common adverse effect - Cyproterone acetate (used widely outside the US) carries a dose-dependent risk of meningioma; patients on this agent should be monitored and, if possible, kept at the lowest effective dose (<25 mg/day) ## References 1. Hembree WC, et al. "Endocrine Treatment of Gender-Dysphoric/Gender-Incongruent Persons: An Endocrine Society Clinical Practice Guideline." J Clin Endocrinol Metab. 2017;102(11):3869-3903. 2. Coleman E, et al. "Standards of Care for the Health of Transgender and Gender Diverse People, Version 8 (SOC-8)." Int J Transgend Health. 2022;23(Suppl 1):S1-S259. 3. Tangpricha V, den Heijer M. "Oestrogen and Anti-Androgen Therapy for Transgender Women." Lancet Diabetes Endocrinol. 2017;5(4):291-300. 4. Irwig MS. "Testosterone Therapy for Transgender Men." Lancet Diabetes Endocrinol. 2017;5(4):301-311. 5. de Blok CJM, et al. "Breast Cancer Risk in Transgender People Receiving Hormone Treatment: Nationwide Cohort Study in the Netherlands." BMJ. 2019;365:l1652.