What is the ruling on bloody discharge that occurs after taking menstruation-delaying pills: is it considered menstruation, or is it pure, thus obligating prayer and fasting?

If the discharge occurs during a period that can be considered menstruation, such as being within the maximum duration of fifteen days for menstruation, or after thirteen days (the minimum period of purity) have passed since the cessation of the previous bleeding, then it is menses (hayd). However, if it occurs during a period that cannot be considered menstruation, then it is irregular bleeding (istihada).