it permissible for a woman to take medicine to prevent menstruation so as to be able to fast the [whole] of Ramadan?

Among the established rulings in Islamic law is that a Muslim woman must break her fast in Ramadan when she gets her monthly period due to the exhaustion and physiological disturbances associated with menstruation. For this reason, it is obligatory for a menstruating woman not to fast—it is a mercy from Allah Almighty.

What some women do nowadays—eating very small amounts of food or drinking and then refraining from eating for the rest of the day—contravenes the wisdom behind relieving women from the obligation of fasting and preserving their physical and psychological health.

A woman is required eat and drink when in her monthly period; she does not sin nor is she blameworthy because she will later make up the missed fast-days. as 'Aisha, the Mother of the Believers, said: "When we were with the Prophet [pbuh] , we used to experience menstruation and were commanded to make up the [missed] fast-days but not prayers" [Bukhari and Muslim].

Conditional permissibility

There is no legal objection to taking medicine or pills to delay menstruation and allowing a woman to complete the fast-days of Ramadan without any interruptions. It is permissible for a woman to resort to such a practice on the condition that a physician determines that this will not harm her at any time. If it does, then it is unlawful to take medicine to delay menstruation because of the legal maxim which states; "Do not harm and do not reciprocate harm" and because the preservation of health is one of the exigencies of the objectives of Islamic law.

Even though it is permissible for a woman to delay menstruation to fast Ramadan, it is better for her to abide by the commands of Allah Almighty and submit to His decree as this earns her a greater reward.

Allah Almighty knows best.