A process for the production of a composition comprising a water-insoluble opioid which comprises the steps of: a) providing a mixture comprising: i) a water-insoluble opioid, ii) a water soluble carrier, and iii) a solvent for each of the opioid and the carrier, and b) spray-drying the mixture to remove the or each solvent and obtain a substantially solvent-free nano-dispersion of the opioid in the carrier.