Is it permissible to write Qur’anic verses and then wash them off with water and drink them, under the pretext of seeking healing through them?

It is permissible to write the Qur'an with pure ink, then place it in water, shake it, and drink it. Some of the Salaf (pious predecessors) used to do this, and it falls under the general meaning of His Almighty's saying: "And We send down of the Qur'an that which is healing and mercy for the believers."