Gender-affirming hormone therapy
How sex hormones and hormone blockers are used, under specialist care, to help transgender and gender-diverse adults align their bodies with their gender.
Gender-affirming hormone therapy uses the same drugs as other endocrine care, oestradiol, testosterone and androgen or gonadotropin blockers, to produce the physical characteristics of a person's gender. It is part of a wider package of specialist care that can include psychological support, voice therapy and surgery. WHO no longer classifies gender incongruence as a mental disorder. This page explains the pharmacology, effects, risks and monitoring in neutral, educational terms.
Context and terminology
In ICD-11, WHO moved gender incongruence out of the mental disorders chapter into a chapter on sexual health, to reduce stigma and support access to care. Gender dysphoria describes the distress some people feel when their body or assigned sex does not match their gender. Care is delivered by specialist services and usually combines assessment, psychological support and, for those who choose it, hormones, voice and communication therapy and surgery.
Pharmacology of feminising therapy
Oestradiol, as tablets, gel or patches, drives breast development and other feminising changes, which can take years to reach their full effect. In many people it also suppresses testicular testosterone through negative feedback on the pituitary. When it does not, testosterone is blocked with an antiandrogen such as spironolactone, or its production is switched off with a GnRH analogue. A testosterone blocker is not used alone without oestradiol, because sex-hormone deficiency weakens bone.
- Likely permanent: breast development, smaller testes, reduced fertility.
- Not changed by hormones: voice pitch, the laryngeal prominence and existing facial hair.
Pharmacology of masculinising therapy
Testosterone, by injection or gel, deepens the voice, increases facial and body hair and muscle mass, enlarges the clitoris and usually stops menstruation by suppressing the ovaries. If bleeding continues, a progestogen can be added. Many of these changes are permanent, including the deeper voice, facial and body hair and scalp hair loss.
- Testosterone raises haemoglobin and haematocrit and can affect liver tests and lipids, so these are monitored.
Risks and monitoring
- Venous thrombosis, heart attack and stroke: risk is raised by smoking, obesity, high blood pressure, diabetes, high cholesterol and migraine.
- Bone thinning if sex-hormone levels are kept too low.
- Oestradiol may raise breast cancer risk; it lowers PSA, so prostate tests can read falsely low.
- Blood tests before starting, then regularly until levels are stable, then at least yearly: hormone levels, liver tests, prolactin with oestradiol, and haemoglobin with testosterone.
- Evidence on long-term risks is still limited, which is why lifelong follow-up is advised.
Fertility and contraception
Hormone therapy usually reduces fertility and the effect may be permanent, so storing eggs or sperm is offered before starting. Neither oestradiol nor testosterone is a reliable contraceptive: a person with a uterus taking testosterone can still become pregnant, so effective contraception is discussed.
Adolescents and puberty suppression
GnRH agonists can pause puberty. Their use for gender incongruence in under-18s is where evidence is most uncertain and practice differs most between countries. In the UK, after reviews found little evidence of benefit and uncertainty about effects on the developing brain and body, the Commission on Human Medicines recommended an indefinite restriction outside a clinical trial. Other countries follow different guidance, and students meet the topic both as pharmacology and as a live policy question.
Test yourself
Think of the answer, then tap the question to see it.
What are the two pharmacological principles of gender-affirming hormone therapy?
Suppress the body's own sex hormones and replace them with those of the affirmed gender.
Why is a testosterone blocker not used alone without oestradiol in feminising therapy?
Without any sex hormone, bone is lost and osteoporosis risk rises; oestradiol protects bone.
Which blood test is especially followed in people taking testosterone, and why?
Haemoglobin or haematocrit, because testosterone raises red cell production and thickens the blood.
Is testosterone therapy a reliable contraceptive?
No. Pregnancy remains possible while taking testosterone, so effective contraception is still needed and is discussed before starting.
Example drugs
- Estradiol
- Testosterone
- Spironolactone
- Leuprorelin
- Triptorelin
- Goserelin
- Finasteride
- Medroxyprogesterone acetate
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Gender-affirming hormone therapy (Sussex Partnership NHS Foundation Trust, 2026); Gender dysphoria and incongruence (NHS, 2026); Gender incongruence and transgender health in the ICD (World Health Organization, 2026); Commission on Human Medicines report into the safety implications of proposed puberty blockers legislation: factsheet (GOV.UK (Department of Health and Social Care), 2025).
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Representative model, for educational purposes only.