dependable information approximately the structure of pharmaceutical compounds is important for patient safety,for the development of related drugs and for patenting purposes. However, working out the structures of pharmaceuticals can be tough. The individual molecules can pack together in the solid in different ways to form different polymorphs, and pertinent properties such as stability,bioavailability or how fast they dissolve in the stomach can vary from one polymorph to another. Single crystals (as used in standard X-ray diffraction experiments) therefore might not be representative of the bulk sample, or indeed might not even be available.
Source: phys.org