In biological sciences, the term small molecule refers to a small non-peptide, organic compound that is biologically active. Small molecules as research materials have many advantages since they can be designed to be selective, potent, water soluble or cell permeable. Consequently they have found useful applications as agonists and antagonists of GPCRs, as well as enzyme inhibitors, nuclear receptor ligands and ion channel modulators. Many commonly used drugs are small molecules because unlike peptides and proteins, they can be designed to be metabolically stable and orally active. As a result, small molecules have become essential components of the biological scientists repertoire.