November 16, 2011 — Highly intelligent children may be at increased risk for using illicit drugs as adolescents and adults, new research suggests.
In a population-based cohort study that included almost 8000 participants, investigators found that high IQ scores at the age of 5 years were significantly associated with cannabis use at the age of 16 years, and with cannabis and cocaine use in women and amphetamine and ecstasy use in men at the age of 30 years.
Moreover, these associations held up even after adjusting for psychological distress during adolescence and life-course socioeconomic position.
“The takeaway message for MDs is that we should not assume that a high IQ will only be associated with healthy behaviors,” lead author James White, PhD, research associate at the Center for the Development and Evaluation of Complex Public Health Interventions at Cardiff University, United Kingdom, told Medscape Medical News.
“For the most part, a high IQ is a very good thing, and has been associated in the past with a healthier lifestyle and robust indicators of cardiovascular risk, such as blood pressure and lipid levels. However, our study and others indicate it can also be associated with drug and alcohol misuse,” said Dr. White.
The study was published online November 14 in the Journal of Epidemiology and Community Health.
Fulfilling a Need for Novelty?
The investigators note that because individuals with high IQs have been shown to score highly on tests of stimulation seeking and openness to experiences, it may be that alcohol and illegal drugs fulfill their desire for novelty and stimulation. Drug use may also be seen as a way of staving off boredom and/or a way to cope with stigmatization from peers.
“There is a clear need for future epidemiological and experimental studies to explore these and other pathways,” the authors write.
“Most previous research has shown high childhood IQ is associated with a healthy lifestyle. For example, high IQ in childhood has been associated with a healthier diet, being more physically active, and being less likely to smoke as an adult,” said Dr. White.
However, because 2 recent studies ( Am J Public Health. 2008;98:2237-2243, Soc Sci Med. 2007;64:2285-2296) suggested that high IQ is associated with an increased risk for excessive alcohol use and alcohol dependency in adulthood, the investigators wanted to explore possible associations with illegal drug use.
“If we know what is associated with drug use, we have more information to guide future research, which will hopefully be helpful in reducing dependency on drugs,” added Dr. White.
The investigators evaluated data on 7904 participants with IQ scores assessed at the age of 5 years and 7946 patients with IQ scores assessed at the age of 10 years from the 1970 British Cohort Study, which measured lifetime drug use and socioeconomic factors up to the age of 30 years.
All participants were enrolled in the study at birth. At the 5-year follow-up, the Human Figure Drawing Test, a Copying Design Test, the English Picture Vocabulary Test, and the Profile Test were administered in-home to assess cognitive function.
At the 10-year follow-up, a modified version of the British Ability Scales was used to evaluate IQ. At the 16-year follow-up, self-reports were collected on level of psychological distress (according to the 12-item General Health Questionnaire) and lifetime use of illegal drugs, such as cannabis, cocaine, uppers and downers, lysergic acid diethylamide, and heroin.
At the final 30-year follow-up, participants were asked about use in the previous year of the already named drugs plus amphetamines, ecstasy, amyl nitrate, temazepam, ketamine, crack, and methadone.
The participants were also asked about polydrug use, which was defined as using 3 or more illicit drugs, and about highest educational achievement, monthly gross salary, and occupational social class.
Increased Cannabis, Cocaine Use
Results showed that higher IQ scores at the age of 5 years were associated with an increased use of cannabis at the age of 16 years for both sexes, and with increased cannabis and cocaine use at the age of 30 years.
When looking at the specific sexes, investigators found that high IQ scores for girls at the age of 5 years were positively associated with use of cannabis (odds ratio [OR], 2.25) and cocaine (OR, 2.35) at the age of 30 years. For boys, it was associated with subsequent amphetamine (OR, 1.46), ecstasy (OR, 1.65), and polydrug use (OR, 1.57).
High IQ scores at the age of 10 years for all participants were positively associated with cannabis use at the age of 16 years, and with cannabis, cocaine, ecstasy, amphetamine, and polydrug use at the age of 30 years.
“In the analyses of drug use at 30 years, associations with IQ at both 5 and 10 years were stronger among women than among men,” report the researchers.
They note that further studies are needed examining the associations between childhood IQ and adult drug use “in different geographical and historical contexts.”
“We need to know more about the exact level of harm associated with infrequent drug use, and we need more detailed research on the long-term harms of illegal drug use in the wider population, rather than just in those dependent on drugs,” added Dr. White.
The study was supported by the British Heart Foundation, Cancer Research UK, Economic and Social Research Council, Medical Research Council, the Welsh Assembly government (under the auspices of the UK Clinical Research Collaboration), and the Wellcome Trust. The study authors have disclosed no relevant financial relationships.
J Epidemiol Community Health. Published online November 14, 2011. Abstract