© 2019 The Royal Society of Chemistry. The polymorphic control of the co-crystal carbamazepine-saccharin (CBZ-SAC) metastable form II was achieved by nano-droplet confinement in tandem with droplet surface charging induced by electrospraying the precursor solution. Polymorphic exclusivity is independent of solvent selection. CBZ-SAC co-crystals obtained by electrospraying are compared with supercritical CO 2 nano spray-drying, conventional spray-drying and solvent evaporation methods.