still lag far behind those available for other complex diseases with a similar public health impact, and no large scale GWAS for CD has been performed. This problem is exacerbated by the fact that controls exposed to illicit drugs (a prerequisite for developing OD or CD) represent a small subset of the total control population. They may also be limited by the lack of differentiation between dependence upon prescription opioids and heroin, which may have a different set of risk factors.
