Is a multiple sclerosis patient who takes medication every 12 hours and fears the effect of fasting on the stability of her health and studies required to fast, or should she wait for recovery and a reduced medication dosage?

The obligation to fast is determined by a trustworthy Muslim physician. If he decides that fasting will not cause harm and that changing medication timings will not have an adverse effect, then fasting is obligatory. Otherwise, you have a dispensation to break your fast. What is obligatory upon you is to make up the missed days, even in the winter, and the fidyah (expiatory feeding) is not sufficient as long as you are able to make up the fast. However, if the inability to fast is continuous and there is no hope of recovery, then you must feed one poor person for each day you miss fasting.