Embodiments of the invention relate to particles of active substances, methods for preparing the particles, formulations containing the particles, and metered dose inhalers containing such particles or formulations. In one embodiment, a composition of an aerosol formulation is provided and contains a particulate active substance of non-micronized, solid particles having a mass median aerodynamic diameter of less than 10 μm suspended in a hydrofluorocarbon fluid vehicle at a concentration within a range from about 0.2% w/v to about 5% w/v. The aerosol formulation exhibits a flocculation volume of about 85% or greater about 1 minute after mixing the particulate active substance and the hydrofluorocarbon fluid vehicle. The particulate active substance contains an alkaloid ergotamine, pharmaceutically acceptable salts thereof, analogs thereof, or derivatives thereof. In some examples, the alkaloid ergotamine contains dihydroergotamine, such as dihydroergotamine mesylate and the hydrofluorocarbon fluid vehicle contains HFA 134a, HFA 227ea, or mixtures thereof.