An apparatus for or method of delivering a substance such as one or more of a triptan a nasal steroid or carbon dioxide gas to the nasal cavity of a subject in particular for the treatment of headaches for example migraine or rhinosinusitis for example chronic rhinosinusitis optionally with polyps the method comprising the steps of fitting a nosepiece to one nostril of the subject delivering the substance through the nosepiece to the posterior region of the nasal cavity of the subject.