Polymorphism may be defined as the phenomenon of existence of two or more crystalline forms of the same compound in which the molecules have different arrangements and/or conformations in the crystal lattice and each crystalline form is known as polymorph.

Polymorphs generally have different physical and chemical properties resulting in different stability and bioavailability of drug products. Polymorphism is a widespread phenomenon observed for more than half of all active pharmaceutical ingredients.

Pseudopolymorphism may be defined as crystalline forms of a compound in which solvent molecules are included as an integral part of the structure. Pseudopolymorphs (solvates and hydrates) can be stoichiometric or nonstoichiometric in nature.

Polymorphisms can be characterized by

Powder X-ray diffraction

Single-crystal X-ray diffraction

Raman spectroscopy

Infrared spectroscopy

Optical microscopy

Scamming electron microscopy

Atomic force microscopy

Hot-stage Microscopy

Thermogravimetric analysis

Differential thermal analysis

Differential scanning calorimetry Isothermal calorimetry

Solid-state nuclear magnetic resonance

spectroscopy