Methods for producing a pharmaceutical preparation of pressure-fused particles including an active pharmaceutical ingredient are disclosed. The methods include the application of a pressure of between 0.1 GPa and 10 GPa to produce a compacted sample. The pressure-fused particles of the invention are useful for parenteral administration, and particularly sustained-release formulations, due to dissolution kinetics which are superior to conventional crystalline or amorphous packed powder preparations of active pharmaceutical ingredients. Pharmaceutical preparations including such pressure-fused microparticles are also disclosed.