Spironolactone

Spironolactone is a tablet originally used for blood pressure and fluid retention that also blocks testosterone. It is the most common [anti-androgen](/glossary/anti-androgen) for feminizing hormones in the US. Often shortened to "spiro".

Where you'll meet it

On most US feminizing prescriptions that include a blocker, and in comparisons with cyproterone, which fills the same role in most other countries.

How it works

It partly blocks testosterone at the cell and partly lowers how much is made. It is a relatively mild anti-androgen, and some people on it still have testosterone above the range their prescriber is aiming for, which is one reason some prescribers move to estrogen alone, called monotherapy, or a different blocker.

The side effects people notice

It is a diuretic, so needing to pee more often is almost universal, especially at first. Some people feel lightheaded when they stand up, because it can lower blood pressure. It makes the body hold on to potassium, which is why potassium is on the blood tests of people who take it, and why prescribers ask about potassium supplements and some other medicines. Dehydration and thirst come up too.

Where it fits

It is cheap and widely available, and for many people it does the job with little trouble. Anti-androgens compares it with the alternatives.

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