Bicalutamide

Bicalutamide is a tablet that blocks testosterone from acting on the body's cells, without lowering the amount of testosterone in the blood. It was developed for prostate cancer, and some prescribers use it off label as the [anti-androgen](/glossary/anti-androgen) in feminizing hormone therapy.

Where you'll meet it

In online discussion more than in guidelines. Some informed-consent clinics and individual prescribers, more often in the US, offer it, often for people who did not get on with spironolactone or cyproterone. It also comes up in non-binary plans, because it blocks rather than removes, and in conversations about avoiding spironolactone's trips to the toilet and potassium checks.

"Off label" means the medicine is licensed for something else and the prescriber is using it for a purpose the licence does not cover. That is legal and common across medicine, but it usually means the evidence for the new use is thinner, and insurers may be less keen to pay.

How it works

Testosterone acts by fitting into the androgen receptor on a cell. Bicalutamide sits in that receptor and stops testosterone using it. It does not act on the brain's signal to the testes the way cyproterone or a GnRH agonist does, so the testes carry on making testosterone, and the blood level can stay in the typical male range or even rise.

Some of that testosterone is turned into estrogen in the body, which, together with the blocked androgen effect, is why bicalutamide tends to cause breast growth on its own. That is wanted by some people and not by others, which matters for non-binary plans.

Why the blood test looks odd

Because the testosterone is still there, the usual check that an anti-androgen is working, testosterone brought under about 50 ng/dL, does not apply. A high testosterone result on bicalutamide is expected, not a failure. Prescribers judge it instead by physical changes, by estradiol levels, and by how you feel. If a new doctor or a lab flag reads your testosterone as a problem, tell them you are on a receptor blocker. How to read your hormone blood results explains the flags.

What gets checked

Bicalutamide can, rarely, cause serious liver injury, so prescribers who use it usually check liver function before starting and regularly afterwards, especially in the first months. Yellowing of the skin or eyes, dark urine, or pain under the right ribs mean getting seen the same day, as the feminizing risks page lists. Rarely it has also been linked to lung inflammation, so a new cough or breathlessness that will not settle is worth mentioning. It does not carry spironolactone's potassium issue or cyproterone's meningioma concern.

The evidence

Most of what is known about it comes from prostate cancer treatment, in patients and at doses quite different from trans women. Studies in trans people are few and small, and the major guidelines, including the Endocrine Society's and WPATH's, do not list it as a standard option. Some clinicians have also questioned its effect on breast development over the longer term, and there is little data either way. That does not make it a bad choice; it means you are on a less-studied path.

Common questions

Blocking is the same as lowering. It is not. If you stop bicalutamide, the testosterone that was there all along acts again straight away, with none of the lag you get after coming off a medicine that suppressed production.

It works without estrogen. On its own it blocks androgens but does not provide the estrogen your bones and feminization need. It is normally prescribed alongside estradiol.

What to ask

Why bicalutamide for you rather than the usual options where you live? How will your liver be monitored, and how often? How will the prescriber judge whether it is working, since testosterone will not tell them? Anti-androgens compares it with the alternatives.

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