That which is required is demanded, obligatory, necessary, and essential: "It is required that all applicants be citizens of this country." "A health certificate will be required." That which is prescribed is recommended, suggested, or designated: "The physician prescribed bed rest for the patient." "This student's prescribed course of study contained several required subjects." A requirement is a demand; a prescription is a direction or recommendation.
Dictionary of problem words and expressions. Harry Shaw. 1975.