What is the ruling on using zakat to purchase medicine for poor patients?

There are eight categories of zakat, which Allah Almighty has specified in His noble Book by saying, "Zakat expenditures are only for the poor and for the needy and for those employed to collect [zakat] and for bringing hearts together [for Islam] and for freeing captives and for those in debt and for the cause of Allah and for the stranded traveler—an obligation [imposed] by Allah. And Allah is Knowing and Wise" (Quran, 9:60).

This means that zakat is primarily intended for the welfare and development of man, rather than for erecting or maintaining buildings. Ensuring that the poor and the needy have sufficient clothing, food, shelter, livelihood, education, medical care, and all other necessities of life should be the foremost concern. This fulfills the fundamental wisdom behind zakat, as indicated by the Prophet (peace and blessings be upon him) who said, “It is taken from the wealthy among them and returned to their poor”
(Bukhari and Muslim). This includes the treatment of poor patients and spending on the medical services they require.

Based on the above, it is permissible to use zakat funds for the treatment of poor patients and for purchasing medicine for them.

And Allah the Almighty knows best.