A process for coating carrier particles with inhalable drug guest particles, the process including providing an apparatus including a processing vessel having solid walls defining a chamber for receiving the particles and adding the particles to the chamber. Next, the cylindrical processing vessel is rotated about an axis to impart a centrifugal force of between 10 and 2100 g on the particles. Further a process coats carrier particles with guest particles, wherein the carrier particles include a material or a drug and wherein the guest particles include a solubility/dissolution controlling agent.