Is a woman’s fast valid if she took pills to prevent menstruation and noticed a brownish discharge on separate days of the last ten days [of Ramadan], and did not perform ghusl, but continued to fast and pray?

It is permissible for a woman to take medication to stop menstruation if no harm results from it, and she is considered pure when the bleeding stops. A brownish discharge during the customary period is considered menstruation, and outside of it, it is not. So, if you see a brownish discharge during your usual menstrual days, your fast is invalid, and you must make up for it, but not the prayer. However, if the brownish discharge occurs after your usual menstrual days have ended, it is not considered menstruation, and your fast is valid.