The use of feminizing hormones in males is linked to a wide array of life-altering and life-threatening harms. These include dramatically increased risks for cardiovascular events, various cancers, irreversible infertility, brain changes, and overall mortality. The severity and breadth of these safety signals underscore the need for extreme caution.

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Cardiovascular Concerns

• Increased risk of venous thromboembolism (potentially >5x higher after two years), escalating over time

• Increased risk of stroke (potentially 10x higher after six years), escalating over time.​

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Reproductive System Harms

• Likely permanent testicular atrophy

• Abnormal sperm production, including cessation of sperm production

• Atypical cells in testicular tissue mimicking germ cell neoplasia

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Cancer

• Elevated rates of testicular (potentially 26.5x higher) 

• Elevated rates of breast cancer (potentially >40x higher)

• Higher prevalence of thyroid cancer, with a higher incidence of the more aggressive subtype

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Neurological Impacts

• Decrease in total brain volume and an increase in ventricle size 

• Cognitive Impairment

• Increased risk of Major Depressive Disorder

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Metabolic and Autoimmune Illness

• Increased fat mass and worsened insulin resistance​​

• Increased incidence of lupus, rheumatoid arthritis, and systemic sclerosis

• Increased risk of hypertriglyceridemia-induced and gallstone pancreatitis

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Mortality

• A large Dutch study found an 80% higher overall mortality risk ​​​

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For current research and references, see Emerging and accumulating safety signals for the use of estrogen among transgender women.