Cyproterone acetate is a synthetic anti-androgen that works by blocking testosterone at the receptor level and simultaneously suppressing the body’s own testosterone production. Developed in the 1960s and first used clinically in the early 1970s, it was the first anti-androgen suitable for clinical use and remains one of the most potent options available for conditions driven by excess androgen activity. It is prescribed across a wide range of medical scenarios, from severe acne and unwanted hair growth in women to prostate cancer, gender-affirming hormone therapy, and certain forensic psychiatric applications. Despite its effectiveness, cyproterone acetate carries a safety profile that demands careful attention, particularly regarding brain tumors, liver damage, and blood clots, and it has never been approved by the FDA for use in the United States.
How Cyproterone Acetate Works
The drug operates through a dual mechanism that distinguishes it from many other anti-androgens. First, it acts as a competitive antagonist at androgen receptors in tissues like skin, hair follicles, fat, and muscle, physically blocking testosterone and its more potent derivative dihydrotestosterone from binding and producing their effects.1PubMed Central. Cyproterone acetate or spironolactone in lowering testosterone concentrations for transgender individuals receiving oestradiol therapy Second, it has strong progestational activity, which suppresses the release of hormones from the pituitary gland that tell the testes or ovaries to produce androgens. In men given a moderate daily dose, this antigonadotrophic action was the dominant effect, producing roughly a 70% drop in baseline testosterone and a 50% drop in dihydrotestosterone.2International Journal of Andrology. Effects of Cyproterone Acetate (CPA) on Pituitary Gonadotrophin Release and on Androgen Secretion Before and After LH‐RH Double Stimulation Tests in Men
This combination of receptor blockade and hormonal suppression is why cyproterone acetate tends to lower circulating testosterone levels far more aggressively than anti-androgens that only work at the receptor. It is also why the drug has effects beyond simple androgen blockade: its progestational properties give it mild glucocorticoid-like activity, meaning it can partially suppress the adrenal stress-hormone axis as well.
What It Gets Prescribed For
Cyproterone acetate shows up in surprisingly different corners of medicine. Its most widespread use globally is probably in dermatology and gynecology. In many countries, a low-dose formulation containing 2 mg of cyproterone acetate combined with 35 micrograms of ethinyl estradiol is prescribed as a combined oral contraceptive pill for women with severe acne or hirsutism (excess body and facial hair). Sufficiently powered studies show high effectiveness of this combination for both conditions.3PubMed. The use of cyproterone acetate/ethinyl estradiol in hyperandrogenic skin symptoms – a review In a long-term study of 140 women with polycystic ovaries treated for up to 60 cycles, acne disappeared in all patients within 12 to 24 cycles. Hirsutism was more stubborn: mild to moderate cases cleared in 36 to 60 cycles, while severe hirsutism decreased substantially but persisted in about 30% of women even after five years, suggesting the two symptoms involve different peripheral mechanisms.4Human Reproduction. Efficacy of the combination ethinyl oestradiol and cyproterone acetate on endocrine, clinical and ultrasonographic profile in polycystic ovarian syndrome A Cochrane review confirmed that the drug, combined with estradiol, produces a subjective improvement in hirsutism compared to placebo, though the confidence limits were large.5PubMed Central. Cyproterone acetate for hirsutism
At higher doses, cyproterone acetate has been used in prostate cancer treatment. It was actually the first steroidal anti-androgen applied to this disease.6PubMed. Cyproterone acetate in the treatment of advanced prostatic cancer: retrospective analysis of liver toxicity in the long-term follow-up of 89 patients Because it rapidly suppresses testosterone, it can achieve what is effectively a total androgen blockade when used as a single agent. Clinical testing found it equivalent to diethylstilbestrol (an older estrogen-based treatment) with considerably less toxicity.7Urologic Clinics of North America. Use of Cyproterone Acetate in Prostate Cancer In one study of 18 patients with advanced disease receiving 300 mg per week, median time to progression was 35 months and median survival was 48 months, comparing favorably with other therapies available at the time.8PubMed. Cyproterone acetate monotherapy in advanced prostatic carcinoma
The drug also has a long history in forensic psychiatry. In a double-blind, placebo-controlled crossover study of 19 men with paraphilias who had reoffended sexually, cyproterone acetate significantly reduced certain aspects of sexual behavior, particularly sexual fantasies.9PubMed. Double-blind placebo crossover study of cyproterone acetate in the treatment of the paraphilias A separate study in a forensic psychiatric cohort found its use was associated with lower levels of desire, frequency of sexual activity, and pleasure from sexual activity.10PubMed Central. The use of cyproterone acetate in a forensic psychiatric cohort of male sex offenders and its associations with sexual activity and sexual functioning
Gender-Affirming Hormone Therapy
Outside the United States, cyproterone acetate is one of the most commonly prescribed anti-androgens in feminizing hormone regimens for transgender women and transfeminine people. It is typically taken alongside estradiol, and recent research has focused heavily on what dose is actually needed. The answer, increasingly, is “less than doctors used to think.” A large European study (the ENIGI study) found that all tested doses, from 10 mg to 100 mg per day, suppressed testosterone below the target threshold of 2 nmol/L when combined with estradiol. The 10 mg dose achieved the same testosterone suppression as the 100 mg dose but with fewer side effects: lower prolactin levels and better HDL cholesterol.11PubMed Central. Toward a Lowest Effective Dose of Cyproterone Acetate in Trans Women: Results From the ENIGI Study A more recent study found that even alternate-day dosing can achieve adequate testosterone suppression, providing further evidence that lower-dose regimens are viable.12PubMed Central. How low can you go? Titrating the lowest effective dose of cyproterone acetate for transgender and gender diverse people who request feminizing hormones
This push toward lower dosing is not academic tinkering. It is driven by the drug’s dose-dependent side effects, particularly the meningioma risk discussed below. The European Medicines Agency’s safety committee has recommended using alternatives where practicable and avoiding doses of 10 mg or higher daily.13The Journal of Clinical Endocrinology & Metabolism. Effect of Spironolactone and Cyproterone Acetate on Breast Growth in Transgender People: A Randomized Clinical Trial For clinicians and patients in regions where the drug is available, this creates a tension: cyproterone acetate at low doses appears to work well with a manageable risk profile, but the regulatory landscape is tightening around it.
How It Compares to Spironolactone
In much of the world, particularly the United States where cyproterone acetate is unavailable, spironolactone serves as the go-to anti-androgen for both dermatological and gender-affirming purposes. The two drugs are not equally potent at testosterone suppression. A randomized controlled trial comparing 25 mg of cyproterone acetate daily to 100 mg of spironolactone daily, both combined with estradiol, found that after 12 weeks, 90% of the cyproterone acetate group had testosterone in the female range (below 50 ng/dL), compared with just 19% of the spironolactone group.14The Journal of Sexual Medicine. Anti-Androgenic Effects Comparison Between Cyproterone Acetate and Spironolactone in Transgender Women: A Randomized Controlled Trial A separate observational analysis found that 90% of the cyproterone group and 40% of the spironolactone group achieved total testosterone below 2 nmol/L.15Endocrine Connections. Cyproterone acetate or spironolactone in lowering testosterone concentrations for transgender individuals receiving oestradiol therapy
This difference matters because spironolactone works primarily by blocking the androgen receptor without strongly suppressing testosterone production itself. Cyproterone acetate does both. The practical gap is real, but spironolactone has its own advantages: it does not carry the meningioma risk, does not typically cause the same degree of prolactin elevation, and is readily available in the US. For prostate cancer, the comparison shifts to drugs like bicalutamide, a non-steroidal anti-androgen. A pilot study found that bicalutamide suppressed the initial PSA surge as effectively as cyproterone acetate when used to prevent tumor flare during LHRH analogue therapy, though the onset was slightly delayed.16Prostate Cancer and Prostatic Diseases. Bicalutamide vs cyproterone acetate in preventing flare with LHRH analogue therapy for prostate cancer—a pilot study
The Meningioma Risk
The safety concern that has reshaped prescribing practices most dramatically is the link between high-dose, long-term cyproterone acetate use and meningioma, a type of usually benign brain tumor. A large French cohort study published in the BMJ found a clear dose-response relationship in women. For cumulative doses below 12 grams, the risk was not significantly elevated. But for cumulative doses of 36 to 60 grams, the hazard ratio jumped to about 11, and for doses above 60 grams it reached roughly 22.17BMJ. Use of high dose cyproterone acetate and risk of intracranial meningioma in women: cohort study To put those cumulative doses in context: someone taking 50 mg per day would reach 36 grams in about two years. Someone on the low 2 mg dose in a combined contraceptive pill would take decades to accumulate that amount, if they ever reached it at all.
This is why the dose conversation in gender-affirming care is so clinically urgent. A transgender woman taking 50 mg daily for several years could accumulate a substantial dose relatively quickly. The same woman taking 10 mg daily, or 10 mg every other day, keeps the cumulative exposure far lower. The European Medicines Agency responded to these data by recommending that cyproterone acetate at doses of 10 mg or higher should only be used after benefit-risk assessment and that clinicians should consider alternatives.18The Journal of Clinical Endocrinology & Metabolism. Effect of Spironolactone and Cyproterone Acetate on Breast Growth in Transgender People: A Randomized Clinical Trial Most meningiomas reported in the literature have been associated with long-term use at high doses (typically 50 mg/day or above), and many have regressed after stopping the drug, consistent with what is known about the progesterone-receptor expression of these tumors.
Liver Toxicity
Mild, transient elevations in liver enzymes occur in roughly 10 to 30% of people taking cyproterone acetate, usually resolving without a change in dose.19PubMed Central. Cyproterone Acetate–Induced Acute Liver Failure: A Case Report and Review of the Literature Severe liver injury is uncommon but can be serious. A French case series of 22 patients with cyproterone-induced liver damage found that 91% had hepatocellular injury, half had severe damage, and three (14%) died.20PubMed. Cyproterone acetate induces a wide spectrum of acute liver damage including corticosteroid-responsive hepatitis: report of 22 cases This pattern is most often seen with high-dose use in prostate cancer rather than the low doses used in dermatology or gender-affirming therapy.
The exact mechanism behind the liver damage is not fully understood. It may involve an idiosyncratic reaction to the drug or its metabolites, and preliminary lab work points to enhanced expression of a growth factor that increases hepatocyte sensitivity to programmed cell death.21PubMed Central. Hepatic failure induced by cyproterone acetate: A case report and literature review Because the reaction appears idiosyncratic rather than purely dose-dependent, even low-dose users should have liver function monitored periodically, though the risk is substantially lower.
Blood Clot Risk
The combination of cyproterone acetate with ethinyl estradiol has been studied for venous thromboembolism (blood clots in veins) risk, with somewhat mixed results. One UK study using a large primary care database found an incidence rate ratio for VTE about twice as high in women using the cyproterone-ethinyl estradiol combination compared to those on conventional oral contraceptives.22PubMed. Venous thromboembolism associated with cyproterone acetate in combination with ethinyloestradiol (Dianette): observational studies using the UK General Practice Research Database A nested cohort analysis similarly found an age-adjusted incidence rate ratio of about 2.2 for the combination versus conventional combined oral contraceptives, though the authors cautioned that residual confounding by indication could not be excluded, since women prescribed this drug often have polycystic ovary syndrome, which itself may carry clotting risk.23Human Reproduction. The risk of venous thromboembolism in women prescribed cyproterone acetate in combination with ethinyl estradiol: a nested cohort analysis and case–control study
A broader epidemiological evaluation across six studies in three European countries found the attributable risk was no higher than 0.04% compared to conventional oral contraceptives, and VTE events were classified as rare or very rare by WHO criteria.24PubMed. Cyproterone acetate with ethinylestradiol as a risk factor for venous thromboembolism: an epidemiological evaluation The absolute numbers are small enough that, for most women, the risk is comparable to what they would face on other combined hormonal contraceptives. The concern is worth knowing about, but it should not overshadow the more distinctive risk (meningioma) that separates cyproterone acetate from its alternatives.
Prolactin Elevation and Adrenal Effects
Cyproterone acetate reliably raises prolactin levels, a pituitary hormone involved in breast development and milk production. This effect is dose-dependent: in the ENIGI study, higher doses produced higher prolactin levels.25PubMed Central. Toward a Lowest Effective Dose of Cyproterone Acetate in Trans Women: Results From the ENIGI Study In rare cases, the prolactin elevation is clinically meaningful. A case report described a prolactinoma (a small prolactin-secreting pituitary tumor) developing in a transgender woman treated with conjugated estrogens and cyproterone acetate, with prolactin levels reaching 133 ng/mL and MRI revealing a 5 mm pituitary mass.26PubMed. Prolactinoma induced by estrogen and cyproterone acetate in a male-to-female transsexual Reassuringly, prolactin levels tend to normalize when cyproterone acetate is stopped, even in cases where the elevation occurs at low doses.27Endocrine Abstracts. A case of prolactin increase with cyproterone acetate: sublingual use of estradiol in transgender woman Regular prolactin monitoring is standard practice for anyone on the drug long-term.
Less widely discussed is the drug’s effect on the adrenal glands. Because cyproterone acetate has glucocorticoid-like properties, it can partially suppress the hypothalamic-pituitary-adrenal axis, the system that manages your cortisol response. In children treated for precocious puberty, the drug caused significant adrenal hypofunction secondary to suppressed ACTH, though none showed clinical symptoms of adrenal insufficiency.28PubMed Central. Effect of cyproterone acetate on adrenocortical function in children with precocious puberty In adult women on long-term treatment, reduced basal cortisol output was seen in about a quarter of patients, but the adrenal glands still responded to stress stimulation, meaning the suppression was partial rather than complete.29PubMed. Long-term effects of cyproterone acetate on the pituitary adrenal axis in adult women The practical implication: if you have been on cyproterone acetate for a long time and need to stop, tapering is wise to avoid any transient cortisol deficit, particularly if you are facing surgery or acute illness.
Pharmacokinetics and What Happens in the Body
After you swallow a dose, cyproterone acetate reaches peak blood levels and then declines in two phases. After a single dose, the terminal half-life is roughly 54 hours, but this extends with repeated dosing. By the third treatment cycle in one study of 15 women taking a combined pill formulation, the terminal half-life had increased to about 79 hours and the volume of distribution (how widely the drug spreads through the body) roughly doubled.30PubMed. Pharmacokinetics of cyproterone acetate and ethinylestradiol in 15 women who received a combination oral contraceptive during three treatment cycles This accumulation effect is one reason the drug works even at low or alternate-day dosing: it builds up in tissue over time. It also means that effects and side effects persist for several days after stopping, not hours.
Pregnancy and Reproductive Safety
Cyproterone acetate is absolutely contraindicated during pregnancy. As an anti-androgen, it can feminize the external genitalia of a developing male fetus by interfering with the androgen signaling that drives normal male genital development. In rabbit studies, cyproterone acetate administered during gestation produced measurable feminization of male fetal genitalia, with treated males showing external features statistically closer to female controls than to untreated males.31PubMed. New method for detecting antiandrogenic effects through the measurement of external genitalia in rabbits Mouse studies similarly showed dose-dependent increases in cleft palate, urinary tract abnormalities, and other malformations when the drug was given during specific windows of early development.32PubMed. Teratogenic effects of cyproterone acetate and medroxyprogesterone treatment during the pre- and postimplantation period of mouse embryos. I. This is why, in clinical practice, reliable contraception is considered mandatory for any woman of reproductive age taking the drug. In the combined contraceptive formulation, the ethinyl estradiol component provides that protection. For women on higher-dose standalone cyproterone acetate, a separate contraceptive method is required.
Why It Is Unavailable in the United States
Cyproterone acetate has never received FDA approval, so it cannot be legally prescribed in the United States. The reasons are partly historical: the drug was developed by a German pharmaceutical company and was approved in Europe and many other countries during the 1970s, but the FDA never granted approval, likely due to a combination of concerns about hepatotoxicity observed in early animal studies and the availability of alternative treatments. This has had a major effect on prescribing culture. American endocrinologists and dermatologists default to spironolactone for anti-androgen needs, while their counterparts in Europe, Canada, Australia, and much of Asia and Latin America reach for cyproterone acetate. As a result, most of the clinical trial data and prescribing experience with cyproterone acetate comes from outside the US, and American patients who have heard about the drug through online communities sometimes seek it through other channels, which complicates medical oversight.
The regulatory gap also means that head-to-head comparisons with American-standard treatments are fewer than you might expect, and the randomized trial that does exist, showing cyproterone acetate’s substantial superiority over spironolactone for testosterone suppression, was conducted in Thailand.33The Journal of Sexual Medicine. Anti-Androgenic Effects Comparison Between Cyproterone Acetate and Spironolactone in Transgender Women: A Randomized Controlled Trial A study directly comparing outcomes on the two drugs over longer time horizons, with safety monitoring, would be valuable but has not been done.
Mood and Psychological Effects
Given that cyproterone acetate substantially alters hormone levels, questions about mood effects are common, particularly among transgender women and people treated for skin conditions. The formal evidence is surprisingly thin. A comparison of cyproterone acetate versus leuprolide acetate (a GnRH agonist) in transgender women found no major adverse effects in either group and no difference in psychological well-being parameters.34PubMed. Cyproterone acetate vs leuprolide acetate in combination with transdermal oestradiol in transwomen: a comparison of safety and effectiveness Patient community reports, however, frequently mention fatigue, low mood, and emotional blunting, effects that are plausible given the drug’s broad hormonal impact but difficult to disentangle from the effects of low testosterone itself, concurrent estrogen therapy, or the psychological experience of medical transition. Clinicians familiar with the drug generally acknowledge these reports but note that they tend to improve with dose reduction, which circles back to the case for using the lowest effective dose.