Drug abuse vs Drug misuse?

Drug abuse deals with overuse, where misuse means to use for a reason other than what it is for. For example, the analgesic (narcotic) morphine. A person who abuses morphine may become an addict and abuse the drug (overuse). But if that person uses the morphine to calm a cough, they would be misusing the medication by using it in a way it was not intended to be used.