Is it permissible to present menstruation before Ramadan, even if that results in a period of purity less than fifteen days, and in that case, should one pray during the bleeding period, considering it as irregular bleeding (istihadah) to complete the fifteen days?

It is permissible for a woman to take a lawful medicine for a legitimate purpose, but it is not permissible to take it in order to break the fast in Ramadan. If she takes it and blood appears, it is considered menstruation, and the rulings of menstruation, such as refraining from fasting and prayer, apply to her. This is unless the blood appears before the minimum period of purity has passed (15 days according to the majority of scholars and 13 days according to the Hanbalis), in which case it is not considered menstruation. The jurists have stated that it is not permissible to drink medicine to induce menstruation near Ramadan for the purpose of breaking the fast. If she drinks medicine for menstruation and menstruates, she is not required to make up for the fasting. Similarly, if she takes medicine to induce a miscarriage and nifas (postnatal bleeding) occurs, she is not required to make up for the prayers. The Hanafi jurists have explicitly stated that if a woman drinks medicine and blood appears during the days of menstruation, it is considered menstruation and her iddah (waiting period) concludes with it.