The 118 A > G polymorphism in the human µ‐opioid receptor gene may increase morphine requirements in patients with pain caused by malignant disease

Abstract

Patients homozygous for the 118 G allele of the mu-opioid receptor need higher morphine doses to achieve pain control. Thus, genetic variation at the gene encoding the mu-opioid receptor contributes to variability in patients' responses to morphine.