The invention provides novel 8-azabicyclo[3.2.1]octane compounds of formula (I): wherein R1, R2, R3, A, and G are defined in the specification, or a pharmaceutically-acceptable salt or solvate thereof, that are antagonists at the mu opioid receptor. The invention also provides pharmaceutical compositions comprising such compounds, methods of using such compounds to treat conditions associated with mu opioid receptor activity, and processes and intermediates useful for preparing such compounds.本發明提供一種下式(I)之8-氮雜雙環[3.2.1]辛烷化合物: (I);其中R1、R2、R3、A及G如說明書之定義,或其醫藥可接受性鹽或溶劑化物,其為μ類鴉片受體之拮抗劑。本發明亦提供一種包括該化合物之醫藥組合物、使用該化合物治療與μ類鴉片受體活性有關之病症之方法、及製備該化合物之方法及所用之中間物。