Pharmacogenetic studies are often underpowered statistically due to the labor-intensive nature of treatment trials. Further, because the design features (including study samples and treatment outcome measures) of the various studies of OPRM1 have differed, the data are not amenable to meta-analysis. Although there appears, overall, to be a modest effect of the Asp40 allele on the response to naltrexone treatment in alcoholics, large, prospective studies are needed to estimate its magnitude more accurately.
