that the degree of heterogeneity observed in the present study was similarly reported by the two previous meta-analyses5,9 (χ2 = 4.35, P = 0.037 and χ2 = 41.72, P = 0.003, respectively). This heterogeneity is suggestive of potential moderating variables that may be influencing the association, including environmental differences. Consequently, it raises questions regarding the ability, at this point in time, to make reliable conclusions regarding an association, or lack thereof, between A118G OPRM1 genetics and opioid dependence.
