Pharmaceutical coamorphous, a kind of single-phase amorphous binary system, is formed between an active pharmaceutical ingredient (API₁) and another solid small molecular compound (API₂ or excipient). As a newly defined solid form, pharmaceutical coamorphous has been one new approach for drug research and development, due to its great potential in the improvement of solubility, dissolution, stability or even bioavailability. Several methods can be used for the preparation of coamorphous drugs, including quench-cooling, solvent evaporation and milling/cryo-milling. In this paper, the definition, preparation, physicochemical characterization and formation mechanism of pharmaceutical coamorphous are addressed. The comparison between coamorphous and solid dispersion or cocrystals is also presented.

Contents
1 Introduction
2 Overview of pharmaceutical coamorphous
2.1 Definition and classification of coamorphous
2.2 Comparison between coamorphous and solid dispersion
2.3 Relationship and differences of coamorphous and cocrystal
3 Formation mechanisms
3.1 Type of interaction
3.2 Flory-Huggins theory
4 Preparation of pharmaceutical coamorphous
4.1 Preparation methods
4.2 Factors affecting the formation of pharmaceutical coamorphous
5 Properties of pharmaceutical coamorphous
5.1 Identification
5.2 Stability
5.3 Solubility and dissolution
6 Outlooks