If the menstrual blood stops and is less than three days due to an external factor, such as taking pills,…

Answer

In the name of Allah, know, my son, that one of the conditions for menstruation is that it should not be less than three days. However, if the pills have affected it and the blood lightens, becomes yellow, or stops but lasts for the full three days, it is still considered menstruation and all its rulings apply. Allah knows best.