Abstract: The present invention provides a particulate substrate suitable for carrying a drug for delivery, comprising a substantially crystalline core and a surface coating, wherein the particulate substrate has a proportion of amorphous character of 2% of greater by weight of particulate substrate, and a process for the production of carrier particles comprising the steps of: a) mixing crystalline particles having an average diameter greater than 10 &mgr;m with at least partially amorphous particles having average diameters less than 10 &mgr;m; b) exposing the mixture to conditions capable of inducing crystallization of the amorphous particles for a predetermined period in order that partial crystallization takes place.