Methods of producing a controlled release formulation for an active substance are disclosed, wherein the methods involve dispersing a discontinuous phase comprising an active substance into a continuous phase so as to form a two-phase liquid system comprising droplets of said discontinuous phase, and allowing nanoparticles provided to the two-phase liquid system to congregate at the phase interface to thereby coat the surface of the droplets in at least one layer of said nanoparticles. The methods utilise a concentration of a suitable electrolyte which enhances the nanoparticle congregation such that the coating of nanoparticles on the surface of the droplets presents a semi-permeable barrier to the active substance, or otherwise utilise a amount of the active substance that is greater than the solubility limit of that active substance in the discontinous phase. Formulations comprising vitamin A (retinol) as the active substance for dermal delivery are specifically exemplified.