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 .