An organic solvent-free method for encapsulating progesterone at high loadings within micron-sizedinert latex polymer beads is reported. This approach makes use of a polymeric surfactant to emulsifycarbon dioxide into an aqueous latex suspension. In this way, preformed ∼4 μm polystyrene (PS)microparticles surface-grafted with poly(N-vinylpyrrolidone) (PVP) were plasticized and swollen followedby rapid partitioning of progesterone into the polymer matrix. The as-prepared polystyrene beadsincorporated over 10% progesterone by weight while maintaining their initial size and morphologicaluniformity. Dissolution experiments were also carried out to obtain the release profile of progesteroneentrapped within the PVP/PS particles.