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 CO₂ nano spray-drying, conventional spray-drying and solvent evaporation methods.