Bicalutamide, a new anti-androgen for trans women and girls

Disclaimer: I am not a doctor, and this is not medical advice. Do not take any medication without appropriate medical supervision.

Zinnia JonesPreviously I’ve looked at low-cost alternatives to GnRH analogue puberty blockers for trans adolescents, including medroxyprogesterone acetate, spironolactone, cyproterone acetate, and norethindrone. One new option for trans girls has recently been studied: bicalutamide (Casodex), an oral nonsteroidal anti-androgen used to block testosterone in cases of prostate cancer.

Bicalutamide works by directly blocking the action of androgens at the androgen receptor. It is not an antimineralocorticoid like spironolactone, a glucocorticoid and synthetic progestin like cyproterone acetate, or a DHT blocker like finasteride or dutasteride. For this reason, bicalutamide may be an option for trans women who can’t tolerate the side effects of other anti-androgens, and past publications on hormonal treatment have listed bicalutamide as having a potential role in HRT.

The newest study by a team at the Indiana University School of Medicine and Riley Hospital for Children is the first to look at bicalutamide as a puberty blocker and feminizing medication in adolescent trans girls. The authors found that bicalutamide at 50mg a day produced suppression of testosterone as well as development of breast tissue:

Results: Of 77 patients with GD identified, 29 were MTF, of whom 14 (48%) aged 15.8 ± 1.9 years (range 12-18.4yr) were treated with bicalutamide 50 mg daily between 2013 and 2017. Of these, 3 were started on estrogen concurrently whereas 11 received bicalutamide alone, 7 of whom have returned for follow up thus far. After an average of 5.7±1.5 months, 86% of the patients (n=6) had breast development consisting of Tanner stage III in 4, Tanner stage II in 1, and Tanner stage III/II of the right and left breast in 1. The 7th patient was noted to have Tanner III breasts at her 2nd follow-up clinic visit 12.5 months after starting bicalutamide. LFTs were obtained on 4 patients, estradiol on 3 patients and testosterone on 2 patients while exclusively taking bicalutamide. LFTs were unremarkable and concentrations of estradiol and testosterone were 26-61 pg/mL and 524-619 ng/dL, respectively.

Bicalutamide is available as a generic medication for less than $20 a month. Given that GnRH analogue puberty blockers can cost thousands of dollars and may not be covered by insurance, this lesser-known anti-androgen may be an economical option for adolescent trans girls. 

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About Zinnia Jones

My work focuses on insights to be found across transgender healthcare, public health, psychiatry, and history of medicine, integrating these many perspectives and guided by the lived experiences of trans people. I live in Orlando with my family, and work mainly in technical writing.
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2 Responses to Bicalutamide, a new anti-androgen for trans women and girls

  1. Catriona says:

    Dear Zinnia, it is great to see you highlighting bicalutamide as an antiandrogen for trans women. I have taken it myself for a couple of years and it has proved itself extremely valuable.

    There are some comments I’d like to add regarding the recent study published by the Indiana University School of Medicine.

    The first is to mention that though the abstract of the study indicates its intention was to examine the usefulness of bicalutamide as a puberty blocker, there is good reasoning that the dosage utilized in the study (50 mg/day) may be inadequate for the task. Thus the study can only really be taken as indicative of the type and degree of feminisation 50 mg/day of bicalutamide might typically produce in teenage trans women going through first puberty (though a few of the participants were also taking estradiol).

    Unless teenage trans women going through first puberty have unusually low T, then a dose of 50 mg/day of bicalutamide is unlikely to be sufficient to prevent masculinisation due to first puberty (with the same efficacy and certainty which GnRH analogues provide). Rather a more relevant dose for bicalutamide to function as a fully effective puberty blocker may be at least 150-200 mg/day.

    You can find some discussion and calculations regarding this likely required dose (of maybe at least 150-200 mg/day) here:

    There are many trans women who take doses of bicalutamide in the 25-50 mg/day range, but these individuals are typically post first puberty (and hence do not require puberty blocking) and generally already have lower T (not so far above female range).

    In summary therefore, the study demonstrates that 50 mg/day bicalutamide is effective as a puberty blocker (though does not prove it as a *fully effective* puberty blocker). We know from the study that bicalutamide was able to significantly block effects of T, significantly increase E2 levels and produce significant feminization/breast development, etc.

    The age range of the subjects in the study was 12 to 18.4 years, with a mean of 15.8 years. That 50 mg/day bicalutamide can have significant effects with this age group is reassuring. But, as per above, it is unlikely, that a dosage of 50 mg/day bicalutamide is sufficient to function as a fully efficacious puberty blocker with the same degree of efficacy which GnRH analogues provide.

    With a dose of 50 mg/day bicalutamide in this age group it is likely that a substantial portion of T remains unblocked at the androgen receptor (AR). In addition, it has been observed that the E2 increase produced by bicalutamide maxes out at only 30 mg/day of bicalutamide. Thus it may be that the observed effects in the study were probably in considerable part, simply related to the observed rise in E2.

    Also, for reference, bicalutamide blocks both T and DHT at the cellular receptor level (i.e. not just T).

  2. Lexie Byrd says:

    Bicalutamide is notorious for causing gynecomastia in adult prostate cancer patients. Prostate cancer patients on bicalutamide often take an aromatase inhibitor to prevent this (unwanted) breast development. (BTW, 150 mg/day was the suggested dosage for cancer patients, but bicalutamide is persistent, and adult transgender women seem to do well on the lower dosage used to treat female hirsutism.)
    I cannot help but wonder what might happen if a teenaged transgirl took an aromatase inducer, forskolin, along with 150 mg/day bicalutamide. I can only base a guesstimate from in vitro studies, but she would have to take at least eight caps a day to notice any effect—but she would be using her own testosterone to make the estradiol she needs for breast development. Could this estradiol be enough in itself, and make additional estradiol redundant? What effect would bicalutamide and forskolin have on spermatogenisis? (Bicalutamide does not make patients sterile, unlike spironalactone.)
    I think this is a topic that certainly merits more research. Please let me know how you feel.
    Take care,

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