Estradiol

Estradiol is the main estrogen the body makes, and the one used in feminizing hormone therapy. It is chemically identical to the hormone produced by ovaries, which is why it is sometimes described as "bioidentical". Spelled oestradiol in the UK.

Where you'll meet it

On every feminizing prescription, and on blood results, where the estradiol level is one of the two numbers (with testosterone) that prescribers watch most.

The forms

• Tablets: swallowed, or held under the tongue, which some prescribers suggest and others do not.
• Patches, gel and spray: through the skin (transdermal), often preferred for people over 40 or with clot risk factors.
• Injections: estradiol valerate or cypionate, into muscle or under the skin, usually weekly or every couple of weeks. Common in the US, rarer on public prescription elsewhere.
• Implants: small pellets under the skin, offered by a few clinics.

The words "valerate" and "cypionate" name an attached chemical that changes how fast the estradiol is released. Once in the body, it is the same hormone.

Not the same as the pill

Contraceptive pills contain ethinylestradiol, a synthetic estrogen with a higher clot risk. It is not recommended for feminizing HRT. If you are offered it, ask why.

Reading the level

Estradiol is reported in pmol/L in the UK, Europe and Australia and in pg/mL in the US; divide pmol/L by about 3.67 to get pg/mL. What the level means depends on when the sample was taken relative to your last dose. How to read your hormone blood results walks through it, and estrogen compares the forms.

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