A delivery device for delivery of substance to the central nervous system (CNS) of a subject, the delivery device comprising: a nosepiece unit for insertion into a nasal airway of a subject and comprising an outlet unit which includes a nozzle for delivering substance into the nasal airway of the subject; and a substance supply unit which is operable to deliver a dose of substance to the nozzle; wherein the delivery device is configured such that at least 30 % of the dose as initially deposited in the nasal airway is deposited in an upper posterior region of the nasal airway, thereby providing a CNS concentration of the substance, and hence CNS effect, which is significantly greater than that which would be predicted from a counterpart blood plasma concentration of the substance. Sumatriptan or its pharmaceutically-acceptable derivatives or analogues for use in the treatment of migraine.