The opium poppy is indigenous to Northern Thailand. Historically, high rates of OD have been observed among the country’s ethnic hill tribe populations living in that region (Westermeyer, 1977). Such groups are likely to have greater genetic, environmental, and phenotypic homogeneity than the Thai population taken as a whole, and this provides potential advantages for gene identification efforts, including their relative geographic and cultural isolation, the reportedly high lifetime prevalence rates of OD (estimated as ≥ 10% as compared to ~0.1–0.2% in the U.S.), the presence of apparent historical bottlenecks (i.e., evolutionary events that produce a reduction in population size and in turn lead to increased genetic homogeneity), cultural prohibitions (albeit currently weakening) against marrying outside of the population, large and intact pedigrees, and the relative absence (e.g., in comparison to U.S. populations) of other drugs of abuse.
