Intravenous immune globulin in autoimmune and inflammatory diseases.

The Authors Reply: Both these letters ask whether there could be different interpretations of our results. In response to Thomas et al.: we first want to stress that we never claimed “a causal relationship between lower rates of criminality and pharmacologic treatment for ADHD.” However, we do think that the most plausible explanation is that medication reduces the risk. Thomas et al. argue that during periods when patients have more symptoms they would be both less likely to take medication and more prone to commit crimes. If this hypothesis is true, we would expect to see similar results with other medications. We tried to address this issue by studying selective serotonin-reuptake inhibitors (SSRIs), but among the patients with ADHD, we did not observe an association between SSRI medication and criminality. Cohen raises the possibility that there is no true association, but that persons who receive ADHD medication are less likely to be caught when they commit crimes. We do not see any possible way to address this theory with our data. Observational studies cannot account for all potential confounders in the selection of individual patients for treatment, so there will always be possibilities for alternative interpretations. Ideally, we would want a randomized, controlled trial. However, such a trial on the association between ADHD medication and criminality is unfeasible because it would require a very large sample, a long follow-up, and the inclusion of patients (criminals with ADHD) who most probably would be noncompliant, even if ethics approval was granted. Thus, the best we can do is to reduce the number of alternative explanations and interpret the available data. For the hypothesis on performance enhancement to be correct, persons who are prescribed ADHD medication would have to increase their crime rate (because of their intention) and at the same time reduce their conviction rate by 30 to 40%. On the basis of our results, together with several randomized, controlled trials showing beneficial effects of ADHD medication on symptoms of ADHD and conduct problems,1-3 we find the interpretation that ADHD medication reduces crime rates more plausible.