Spironolactone is a hormone blocker, though not in the way most people picture one. It blocks two types of hormones: aldosterone (a hormone that regulates salt and water balance) and androgens (male sex hormones like testosterone and its more potent form, DHT). This dual blocking action is why spironolactone shows up in such different medical contexts, from treating heart failure to clearing hormonal acne to supporting gender-affirming care.
How Spironolactone Blocks Hormones
Hormones work by attaching to receptors on your cells, like a key fitting into a lock. Spironolactone works by sitting in those locks first, preventing the actual hormones from attaching and triggering their effects. It does this at two receptor sites.
At the mineralocorticoid receptor, spironolactone blocks aldosterone. Aldosterone normally tells your kidneys to hold onto sodium and release potassium. When spironolactone blocks this signal, your body retains less fluid and your blood pressure drops. This was the drug’s original purpose when it was developed as a blood pressure medication.
At the androgen receptor, spironolactone blocks testosterone and DHT from binding to cells throughout the body. DHT is the androgen most responsible for oil production in skin, hair growth on the face and body, and hair loss on the scalp. Beyond receptor blocking, spironolactone also appears to interfere with androgen production itself, reducing the amount of testosterone your body makes. This combination of blocking androgens at the receptor and reducing their production is what makes it effective for androgen-related conditions.
What It’s Prescribed For
Spironolactone’s hormone-blocking properties make it useful across several areas of medicine, and the reason you’re taking it determines the dose.
For hormonal acne and excess hair growth (hirsutism), typical doses range from 100 to 200 mg daily. Women with acne driven by androgens often see results within several weeks, though the full effect on skin can take up to five months. For hirsutism, studies show that women on spironolactone experience slowed hair growth, thinner hair shafts, and no further darkening or coarsening of body hair. It’s commonly combined with an oral contraceptive, which both prevents pregnancy (important, as the drug can harm a developing fetus) and adds complementary hormonal effects.
For heart failure, spironolactone’s aldosterone-blocking ability is the star. Aldosterone contributes to high blood pressure, scarring of heart tissue, inflammation in blood vessels, and thickening of the heart’s walls. By blocking these effects, spironolactone reduces hospitalization for heart failure by about 17% based on a meta-analysis of 14 clinical trials involving over 6,400 patients. It also helps reverse some of the structural damage to the heart and improves how well the heart fills with blood between beats.
In gender-affirming care for transgender women, spironolactone is one of the most commonly prescribed anti-androgens in the United States. Doses range from 100 to 300 mg daily, sometimes up to 400 mg. At these higher doses, spironolactone blocks androgen receptors and may also activate estrogen receptors to some degree. The androgen blockade prevents masculinizing effects and supports feminization when combined with estrogen therapy.
Side Effects From Hormone Blocking
Most of spironolactone’s side effects are a direct consequence of its hormone-blocking activity. Because it reduces androgen signaling throughout the body, it can cause breast swelling and tenderness in both men and women. In men, this can progress to noticeable breast tissue growth (gynecomastia) and erectile difficulty. In women, menstrual irregularity is common, particularly at higher doses.
Decreased sex drive and changes in sexual function affect some users regardless of sex. These effects generally improve if the dose is lowered or the medication is stopped.
Because spironolactone blocks aldosterone’s signal to release potassium, potassium levels in your blood can climb too high. This is the most medically serious side effect and the reason your doctor will check your potassium levels within the first week of starting or adjusting your dose, then regularly after that. The risk increases if you take other medications that also raise potassium or if your kidneys don’t function well.
Potassium and Diet Considerations
Since spironolactone causes your body to retain potassium instead of flushing it out, you may need to be mindful of potassium-rich foods. Salt substitutes are a particular concern because many of them replace sodium with potassium chloride, which can push levels dangerously high when combined with spironolactone. Large amounts of bananas, oranges, potatoes, and leafy greens are worth discussing with your prescriber, especially if your potassium levels run on the higher side at baseline. Your blood work will guide how strict you need to be.
Why It’s Not Safe During Pregnancy
Spironolactone’s androgen-blocking effects make it dangerous during pregnancy. Androgens play a critical role in the development of male genitalia in a fetus, and blocking them during key windows of development can cause feminization of a male baby. Animal studies have consistently shown this effect, and at least two documented human cases have reported male newborns with ambiguous genitalia after their mothers took spironolactone in early pregnancy. One case involved exposure through the first five weeks, the other through eight weeks of gestation. For this reason, women of childbearing age are typically prescribed spironolactone alongside reliable contraception.
How It Compares to Other Hormone Blockers
Spironolactone is not a “pure” anti-androgen. It was designed as an aldosterone blocker that happens to have significant anti-androgen effects. This sets it apart from medications developed specifically to block androgens, which tend to be more targeted but come with their own trade-offs. Spironolactone’s advantage is decades of clinical experience, a well-understood safety profile, and relatively low cost. Its disadvantage is that the aldosterone-blocking side of its action means potassium monitoring and fluid balance changes come along for the ride, even when you’re taking it purely for skin or hair concerns.
For people using it as part of feminizing hormone therapy, spironolactone is the most common choice in the U.S., though other anti-androgens that work through different mechanisms are preferred in some countries. The choice often depends on a person’s tolerance of side effects and how their body responds to treatment.