Ethisterone, also known as ethinyltestosterone, pregneninolone, and anhydrohydroxyprogesterone and formerly sold under the brand names Proluton C and Pranone among others, is a progestin medication which was used in the treatment of gynecological disorders but is now no longer available.

[19][20] Ethisterone was used in the treatment of gynecological disorders such as irregular menstruation, amenorrhea, and premenstrual syndrome.

[6] Side effects of ethisterone reportedly include symptoms of masculinization such as acne and hirsutism among others.

[26] Its total endometrial transformation dosage per 10 to 14 days in women is 200 to 700 mg.[27][additional citation(s) needed] Ethisterone has about 20-fold lower potency as a progestogen relative to norethisterone.

[24] Based on in vitro research, ethisterone and norethisterone are about equipotent in their EC50Tooltip half-maximal effective concentration values for activation of the androgen receptor (AR), whereas, conversely, norethisterone shows markedly increased potency relative to ethisterone in terms of its EC50 for the progesterone receptor.

[2] Interestingly, ethisterone showed antiandrogenic activity when co-administered with dihydrotestosterone (DHT) in animals, whereas 5α-dihydroethisterone did not.

[29] In accordance, high doses of norethisterone have been found to be associated with marked increases in urinary estrogen excretion (due to metabolism into ethinylestradiol), as well as with high rates of estrogenic side effects such as breast enlargement in women and gynecomastia in men and improvement of menopausal symptoms in postmenopausal women.

[34] Ethisterone has relatively high affinity for sex hormone-binding globulin, about 14% of that of dihydrotestosterone and 49% of that of testosterone in one study.

[34] Ethisterone was synthesized in 1938 by Hans Herloff Inhoffen, Willy Logemann, Walter Hohlweg, and Arthur Serini at Schering AG in Berlin.

[41] As such, it was developed as a progestogen instead and was introduced for medical use in Germany in 1939 as Proluton C and by Schering in the United States in 1945 as Pranone.

[36][37][4] Ethisterone has been marketed under a variety of brand names including Amenoren, Cycloestrol-AH Progestérone, Duosterone, Estormon, Etherone, Ethisteron, Luteosterone, Lutocyclin, Lutocylol, Lutogynestryl, Menstrogen, Nugestoral, Oophormin Luteum, Ora-Lutin, Orasecron, Pranone, Pre Ciclo, Prodroxan, Produxan, Progestab, Progesteron lingvalete, Progestoral, Proluton C, Syngestrotabs, and Trosinone among others.