What is the ruling on taking medication that causes the patient to fall into a deep sleep and miss the Fajr prayer because of it?

It is necessary to ascertain from trustworthy doctors that there is no alternative to the medication and that refraining from it will cause harm. If this is confirmed, then there is no objection to using it, while taking precautions for prayer by taking it early in the night and taking measures to wake up, and performing the prayer immediately upon waking.