A preparation for the transdermal delivery into the body of a patient comprises particles 4 of a formulation that is soluble or biodegradable in the body. The particles are irregular in shape and are angular so that they are capable of penetrating the skin 2 of the patient. Preferably, the formulation comprises a biologically active substance, including at least one excipient. A transdermal patch 6 may comprise the preparation, and may have a body, and means for adhering the body to the skin of a patient. The particles of the preparation may penetrate the outer layer of the skin when subjected to pressure from a roller 8 or an array of blunt-tipped microstructures (12, fig 3). Preferably, the angular particles of the formulation are formed by milling a solid aggregate.
