This invention provides for certain phthalazine-containing compounds of the formula (I) or a pharmaceutically acceptable salt, ester or solvate thereof, wherein G is an optionally substituted N-N containing heteroaryl group and the variables are defined herein; the inventive compounds are agonists of the G-protein coupled receptor 40 (GPR40, also known as free fatty acid receptor FFAR). This invention further relates to pharmaceutical compositions containing these compounds, and the use of these compounds to regulate insulin levels in a mammal. The compounds may be used, for example in the prevention and treatment of Type 2 diabetes mellitus and in the prevention and treatment of conditions related to Type 2 diabetes mellitus, such as insulin resistance, obesity and lipid disorders.