Crystalline particles of N-(17-cyclopropylmethyl-4,5.alpha.-epoxy-3,14-dihydroxy-morphinan-6.beta.-yl)-phthalimide or a pharmaceutically acceptable saltthereof aredisclosed. The crystalline particles have a particle diameter distribution inwhich aparticle diameter (D50) at the point where cumulative frequency of volumedistribution cumulatively calculated from particles having a smaller diameterreaches50% is within a range of 1 to 30 µm, and a particle diameter (D90) at thepoint wherecumulative frequency of volume distribution cumulatively calculated fromparticleshaving a smaller diameter reaches 90% is not more than 90 µm, whichcrystallineparticles have a degree of crystallinity of not less than 80%. By thecrystallineparticles, bioavailability of the active substance may be increased whileensuringstorage stability of the compound.
