AimMifepristone, a synthetic steroid compound that induces abortion, was recently found to potentially pass into human milk. This study aimed to determine the effects of mifepristone administration to lactating mice on the development and reproduction of their progeny. MethodsLactating mice were gavage fed with mifepristone (8mg/kg) daily for 4days either from days 1-4 or from days 7-10 of lactation; controls received only peanut oil. Growth, mortality rate, organ weight to bodyweight ratio, sex hormone at 20, 40 and 60days, fertility of these F-1 progeny and litter size, sex ratio and mortality rate of the second generation were recorded. ResultsNo significant differences were observed in the average bodyweight, mortality rate of the female or male pups, and organ coefficient of uterus and ovaries of females in adulthood in comparison with the controls. However, the organ coefficient of testis at day 20 and 40 and testosterone concentration at day 60 were increased in male pups. Moreover, the reproductive capacity of the F-1 pups was unaffected by 4days exposure to mifepristone via their mother's milk: time to birth of F-2 pups, litter size, sex ratio and mortality rate were similar to control F-1 pups. ConclusionThe study showed that treating lactating mice with 8mg/kg mifepristone influenced only the organ coefficient of testis at day 40 and the testosterone concentration in male pups at day 60, however, it did not affect the development and fertility of female and male pups.