NOVELTY - Preparing pharmaceutical co-crystal composition, involves: simultaneously contacting a supercritical or liquefied gas with solid particles of pharmaceutically active component and with solid particles of co-builder to form co-crystallization medium; transforming the solid particles of the component and co-builder into co-crystals by keeping the gas in supercritical or liquid state; and separating the co-crystals, where at least a fraction of the active component and at least a fraction of the co-builder remain in an undissolved state during the co-crystallization.    USE - For preparing pharmaceutical co-crystal composition (claimed).    ADVANTAGE - The method enables easy preparation of a pharmaceutical co-crystal composition that contains virtually no solvent residue. The present method does not require the use of liquid solvents and thus enables production of solvent-free co-crystals under very mild conditions. The method enables the production of co-crystals of poorly water-soluble active components that have considerably higher oral bioavailabilty than crystals made of the pure component.    DETAILED DESCRIPTION - Preparing a pharmaceutical co-crystal composition, involves: simultaneously contacting a supercritical or liquefied gas with solid particles of an active component and with solid particles of a co-builder to form a co-crystallization medium containing the active component and the co-builder as well as solid particles of the active component and solid particles of the co-builder; transforming the solid particles of the active component and the solid particles of the co-builder into co-crystals of the active component and co-builder by keeping the supercritical or liquefied gas in a supercritical or liquid state until at least 80 (preferably at least 90 wt.%) of the active component is incorporated in the crystal matrix of the co-crystals; and separating the co-crystals from the supercritical or liquefied gas, where at least a fraction of the active component and at least a fraction of the co-builder remain in an undissolved state during the co-crystallization.