By Dr. David Rabiner
In childhood, ADHD is often associated with significant oppositional behavior. And, these behavior problems frequently escalate into more serious conduct disturbance and criminal behavior during adolescence and adulthood. Although medication treatment for ADHD has been shown to yield benefits in many areas of individual's functioning, the impact of treatment on adult criminal behavior has not been carefully investigated. This is an important omission in the treatment literature.
The New England Journal of Medicine recently published an excellent study on this issue. As discussed below, results from this study strongly suggest that medication treatment reduces criminality in adults with ADHD [Lichtenstein et al., (2012) Medication for Attention Deficit-Hyperactivity Disorder and Criminality, New England Journal of Medicine, 367, 2006-2014].
The study was conducted in Sweden where national data bases that track psychiatric diagnoses, ADHD prescriptions, and criminal convictions make it ideal for conducting a large, population-based investigation of this question.
The authors began by identifying over 25,500 individuals born before 1990 who had a recorded diagnosis of ADHD in the National Patient Register; over 9,000 were female. Comparison subjects for each participant were identified from a population data base that enabled researchers to match them on age, sex, and geographic location.
For all participants, convictions for criminal offenses between 2006 and 2009 were identified using a national crime data base. During this period, members of the sample ranged from 15 to more than 40 years old.
Information on subjects' medication treatment during this 3-year period was obtained using the Prescribed Drug Register, a national data base that tracks all medication prescriptions in Sweden. Individuals were considered to be receiving medication treatment during the time interval between two prescriptions for ADHD medication, as long as those prescriptions were less than 6 months apart.
For example, if an individual filled a prescription at Time 1 and a second prescription 3 months later at Time 2, the interval between Time 1 and Time 2 was considered a treatment period. If that same individual did not fill a third prescription until 7 months later, the interval between Time 2 and Time 3 would be consider a non-treatment period.
Nearly 40% of women and 50% of men with ADHD never received ADHD medication between 2006 and 2009; fewer than 5% of each gender were treated continuously. The remaining participants had both treatment and non-treatment periods using the definition provided above.
Question 1 - Are rates of criminal convictions higher among adults with ADHD than comparison adults?
The answer to this question was distressingly clear. Among males, 36.6% were convicted of at least one crime between 2006-2009 compared to less than 9% of comparison males. Among females, the corresponding percentages were 15.4% and 2.2%.
Question 2 - Does ADHD medication treatment reduce criminal behavior in individuals with ADHD?
The researchers examined this question in two ways. First, they compared rates of criminal behavior that occurred during all treatment and non-treatment periods across all participants with ADHD. For men, the analysis was based on over 56,000 periods. For women, it was based on over 23,500 periods. By comparing prescription dates for each individual with dates that they engaged in criminal behavior, the researchers determined whether crimes occurred during treatment or non-treatment periods. (Note - The number of treatment and non-treatment periods is greater than the number of participants because each participant could have multiple treatment and non-treatment periods depending on how often they started and stopped medication.)
The results were clear - during treatment periods, the likelihood of being convicted of a crime was approximately 30% lower for men and 22% lower for women.
Within Person Analyses
One limitation with the above analysis is that the treatment and non-treatment comparisons are made across different individuals. Individuals who consistently use medication may differ in important ways from those who do not, and these differences may better explain the different rates of criminal behavior than medication treatment per se.
To address this potential confound, the researchers adopted the clever solution of comparing the rates of criminal behavior in the same individuals during treatment and non-treatment periods. Thus, in this analysis, each person essentially serves as his or her own control. With this approach, if rates of criminal behavior differ based on whether medication treatment is currently in place, it is more likely to reflect an actual medication effect rather than reflecting other differences between individuals who are more vs. less likely to use medication.
Using this method, rates of criminal behavior were 32% lower in men during treatment periods compared to non-treatment periods; in women, the reduction was 41%. Follow up analyses indicated that these reductions held whether the transition was from a medication to a non-medication period or the other way around. And, similar reductions were found regardless of whether the initial or subsequent episodes of medication treatment were considered.
Finally, the authors tested whether findings were specific to ADHD medication, or also occurred for other psychiatric drugs that individuals with ADHD were prescribed; this analysis focus on the use of SSRIs, a class of drugs commonly used to treat depression and anxiety. In contrast results found for ADHD medication, there was no evidence of any association between SSRI treatment and criminal behavior in adults with ADHD.
Question 3 - Is there a long-term effect of ADHD medication treatment on criminal behavior?
The analyses presented above suggest that criminal behavior is less likely to occur during periods when ADHD medication treatment is in place. Another important question is whether medication treatment provides any long-term protective effect against criminal behavior.
To examine this question, the authors tested whether medication treatment status on January 1, 2006 - the start of the 3-year window - predicted rates of criminal behavior during 2009. If medication treatment provided long-term protective benefits, than those in treatment on this start date should have lower rates of criminal behavior in 2009 than those not in treatment. There was no evidence that this was the case.
Summary and Implications
Results from this study provide strong evidence that medication treatment for ADHD reduces the risk of criminal behavior in adults during periods when treatment is in place. However, there was no evidence that treatment provides a long-term protective benefit. This is consistent with much of the literature on ADHD medication treatment i.e. whatever benefits accrue typically do not persist significantly beyond the termination of treatment.
Strengths of this study include a large and nationally representative sample; this provides great confidence in the results that were obtained. The authors were also careful to rule out factors other than ADHD medication treatment that could explain the reduction in criminal behavior that was evident during treatment periods. This included using within person analyses, testing whether the order of change of medication status mattered (it did not), and whether similar effects were found for a different class of psychiatric medication (they were not).
While these are important strengths, the authors recognize that because this was not a randomized controlled trial, all possible confounding factors cannot be conclusively eliminated. However, a randomized controlled trial could not be conducted as it would be unethical and impossible to randomly assign groups of adults with ADHD to take or not take medication for such an extended period. Thus, a study like the one reported here represents the about the best that one can do.
No information was provided on why medication may yield reduced criminal behavior. One explanation is that adults' overall functioning was better when taking medication, and this reduces their engaging in criminal acts. Because many criminal acts result from impulsive behavior, the reduction in impulsivity that medication is likely to produce could also be a contributing factor.
The authors note that because their study took place in Sweden, caution is required about assuming similar findings would occur in the US and elsewhere. However, there is no particular reason to assume that the results are unique to Sweden, as Sweden does not appear to be unusual in its rates of ADHD or ADHD medication treatment.
Finally, it should be noted that the authors did not consider whether nonmedical treatments for ADHD might have a similar impact on criminal behavior. For example, cognitive-behavioral treatment has been shown to be helpful to adults with ADHD and may yield similar, or even greater, reductions in criminal behavior. And, it is possible that such treatment could have more enduring effects since new skills are being learned. This would be an important question to examine in subsequent research; in the meantime, one should not assume that medication is the only way to obtain the benefits reported here.
In summary, results suggest that medication treatment for ADHD significantly lowers the rate of criminal behavior in adults with the disorder. However, there is no evidence that medication treatment conveys benefits that extend beyond the time that it is in place. These are important factors to consider in treatment planning for adults with ADHD, particularly those with a history of antisocial behavior. In future research, it would be beneficial to investigate whether psychosocial treatments can provide similar benefits.
David Rabiner, Ph.D., is an associate research professor and the Director of Undergraduate Studies in the Department of Psychology and Neuroscience at Duke University and has published the Attention Research Update since 1997.