From: Rabbi Akiva Eiger
To: Unknown recipient
Rabbi Akiva Eiger defends the Rema's ruling that a non-dangerously ill person may derive benefit from rabbinically prohibited items but may not eat or drink them. He marshals a proof from the Yerushalmi regarding nursing after twenty-four months, showing that even a rabbinic prohibition may not be consumed absent mortal danger, and constructs a mimmah nafshach argument showing this holds under both versions of the relevant Talmudic dispute.
Source: Shu"t Rabbi Akiva Eiger §55