There is a very interesting and informative study in the most recent issue of the European Child & Adolescent Psychiatry titled, ADHD in international adoptees: a national cohort study The abstract is summarized below:
Several investigators have reported an increased frequency of attention/hyperactivity symptoms in internationally adopted children. In this national cohort study, the authors aimed to determine the prevalence of ADHD medication in international adoptees in Sweden, in comparison to the general population. A further purpose was to study gender, age at adoption and region of origin as predictors of ADHD medication in international adoptees. The study population consisted of all Swedish residents born in 1985–2000 with Swedish-born parents, divided into 16,134 adoptees, and a comparison population of 1,326,090. ADHD medications were identified in the Swedish Prescribed Drug Register during 2006. Logistic regression was used to calculate the "odds ratios".
The rates of ADHD medication were higher in international adoptees than in the comparison population for both boys (5.3 vs. 1.5% for 10–15-year olds) and girls (2.1 vs. 0.3% for 10–15-year olds). International adoptees from all regions of birth more often consumed ADHD medication compared with the majority population, but the age and sex adjusted odds ratios were particularly high for adoptees from Eastern Europe, Middle East/Africa and Latin America. Adjusting for maternal education and single parenthood increased the odds ratios even further. The risk also increased with higher age at adoption. Adoptees from Eastern Europe have a very high risk for ADHD medication. A structured identification and support programme should be tailored for this group. Adoptees from other regions have a more moderately increased risk, which should be communicated to adoptive parents and to professionals who care for adoptees in their clinical practice.
Of course it is still unclear whether the children actually had ADHD since attention difficulties and related "ADHD" symptoms can also be caused by sensory-integration dysfunction, trauma symptoms, Complex Trauma, attachment difficulties and disorders, and Bipolar disorder. The fact that the children from Eastern Europe had the highest rate of use of ADHD medication does suggest some environmental rather than a genetic cause for the attention problems; suggesting that the cause may lie with the effects of chronic early maltreatment on development (Complex Trauma)