A method of making a sustained release microsphere formulation, wherein the release rate of a bioactive ingredient is manipulated by controlling the crystallinity of said bioactive ingredient, includes the steps of combining the active ingredient and an encapsulating polymer in at least one solvent, or mixtures thereof, to form a dispersed phase and processing the dispersed phase without filtering, filtering the combined dispersed phase with a hydrophobic or a hydrophilic filter, or filtering the active ingredient and encapsulating polymer individually with a hydrophobic or hydrophilic filter before combining them to form the dispersed phase. The dispersed phase is then combined with a continuous phase to form the microsphere formulation.
