A method of reducing the respiratory depressant effect associated with diamorphine (diacetylmorphine morphine diacetate or heroin) administration wherein the method comprises administering intranasally a single dose pharmaceutical composition comprising (a) lyophilised diamorphine or a pharmaceutically acceptable salt thereof; and (b) a diluent for reconstitution comprising a preservative a chelating agent one or more osmolarity modifiers and a pH modifier. Preferably the osmolarity modifiers a...