[Q]: What is the ruling on using medication solely in the month of Ramaḍān to prevent [the onset of] menses in order to fast the entire month?

[A]: Allāh has allowed women to break their fast during the days of their menses and postnatal bleeding, and indeed, the Prophet (صلى الله عليه وسلم) said: “I have not seen anyone more deficient in intelligence and religion than you. A cautious sensible man could be led astray by some of you.” They asked: “What is deficient in her intelligence and religion?” He said: “As for her deficiency in intelligence, then verily, Allāh has made the witness of two women equal to that of one man. As for her deficiency in her religion, then certainly, she remains for days without fasting or praying.” [Reported by al-Bukhārī and Muslim.]

Therefore, Allāh has allowed the woman to break her fast during the days of her menses and postnatal bleeding. Consequently, it is not necessary for her to take tablets in order to fast the entire month, bearing in mind that these tablets —which a lot of women take— have a negative effect upon the woman, hence, it is necessary for her to avoid them.

Source: Fatāwá al-Ṣiyām pg 58.
Translated by: Abū Wāʾil Musa Shaleem