Studies of the components of an oral contraceptive agent in albino rats. I. Estrogenic component

In this study from 1980, albino rats were fed ethynylestradiol at doses 10 to 100 times higher than the human dose used in oral contraceptives for 2 years. The treatment resulted in dose-related estrogenic effects such as growth retardation, alopecia, liver enlargement, and increased survival rates. Female rats experienced uterine changes and gonadal atrophy, while males showed gonadal atrophy and an increased incidence of mammary tumors. Both sexes at higher doses developed liver neoplastic nodules and pituitary adenomas, but overall tumor incidence did not increase compared to controls. Interestingly, treated females showed a delayed onset and reduced potential for tumor development compared to control females.