A preparation for the transdermal delivery of a biologically active substance into the body of a patient comprises particles of a formulation comprising the active substance. The particles are irregular in size and shape and may be produced by a low cost manufacturing method such as grinding from a thin film. The particles are angular, i.e. they have sharp edges and corners that allow them to penetrate the outer layer of the skin when subjected to pressure from a roller or an array of blunt-tipped microstructures. Sucrose may be used as an excipient with the active substance to form suitably rigid and angular particles.