Child drug use ‘aggression link’ 01/02/06

• It was reported on the 2nd February [1] that a study by Dutch researchers had shown that cannabis use increased the risk of aggressive behaviour in young people, and “caused” problems such as delinquency and aggression
• The article was based upon a Dutch questionnaire survey of over 5500 12 – 16 year olds and collected data on cannabis use and psychological and behavioural problems [2]. The authors concluded that there was a strong link between frequency of recent cannabis use and the reporting of aggressive behaviours
• The media report was erroneous in describing cannabis as ‘causing’ problem behaviours. This was not the conclusion of the authors and the study design only allowed identification of statistical associations, which could be interpreted in a number of ways. Furthermore, other data that may have also explained the results obtained was not collected.

1. Title, Authors, and Source

Monshouwer K, Van Dorsselaer S, Verdurmen J, Ter Bogt T, De Graaf R, Vollebergh W (2006) Cannabis use and mental health in secondary school children: Findings from a Dutch survey. British Journal Of Psychiatry, 188:148-153

2. What were the study objectives?

A study conducted as part of a WHO cross-national study Health Behaviour in School aged Children (HBSC). The primary objective was to investigate the association between cannabis use and mental health in adolescence.

3. What was the nature of the evidence?

The population consisted of 5551 adolescents aged 12-16 years drawn from the Dutch HBSC survey. The outcome measures were mental health and cannabis use. Mental health was measured using the Youth Self Report (YSR) method. The YSR consists eight sub-scales concerned with internalising problems such as depression, externalising problems such as aggressive behaviour, social problems, thought problems and attention problems.  Cannabis use was measured using by asking ‘How many times did you use cannabis?’ in two time periods, lifetime and last year. On the basis of these answers, participants were allocated to one of five cannabis subgroups; abstainers; discontinued user; experimental user; regular user; heavy user. To adjust for confounding factors additional questions concerned with alcohol consumption, smoking levels, sociodemographic levels and family influence were added. Analysis was conducted using multivariate linear regression, using cannabis as an independent variable. 

4. What interventions were examined in the research?

None, this was a retrospective self-reported study of cannabis use and mental health

5. What were the findings?

18% of the population had ever used cannabis. 3% had discontinued use, 5% were experimental users; 7% were regular users, and 2% were heavy users. The study found significant associations between delinquent and aggressive behaviour and last year cannabis use, which became stronger alongside increasing frequency of use. These largely remained after controlling for factors such as age, gender, and affluence. There was no increase in YSR score as between regular and heavy users. The study also found associations with cannabis use and attention problems moderate associations with thought problems and weak associations with depressive disorders. 

6. What were the conclusions?

The study concluded that at young ages the recent regular and heavy use of cannabis is strongly associated with delinquent and aggressive behaviour. There was no association between age and behavioural findings

7. How reliable are the conclusions?

• The reliability of the study can be criticised by its reliance on school based self–report data (response rate 45%), which may have led to a false reporting on responses to several sensitive questions and an under-representation of groups such as truants, who may have reported different levels of cannabis use.
• The study authors did not ask questions about other use of drugs which may have contributed to the results.
• No assessment was made of age of first use; if these results were related to frequency of use then long term users may be expected to report greater problem behaviours.  Earlier ages of drug initiation are also associated with greater likelihood of problematic drug use and behaviours.
• No assessment was made of concurrent personality disorder, health status, and psychopatholgogy whose aetiology may have been unrelated to drug use. 
• As this study had a cross sectional design it is not possible to make inferences on causal relationships. Young aggressive individual may be more likely to be heavy users of cannabis than non aggressive individuals.

8. Systematic reviews

NCCDP researchers searched for systematic reviews relevant to this topic. Systematic reviews are valuable sources of evidence as they locate, appraise and synthesize all available evidence on a particular topic. There were no additional related systematic reviews identified on the Cochrane Database of Systematic Reviews (CDSR).

References

1. BBC News 1/02/06 (online) Child drug use ‘aggression link’ http://news.bbc.co.uk/1/hi/health/4666140.stm accessed 01/02/06
2. Monshouwer K, Van Dorsselaer S, Verdurmen J, Ter Bogt T, De Graaf R, Vollebergh W (2006) Cannabis use andmental health in secondary school children: Findings from a Dutch survey. British Journal Of Psychiatry, 188:148-153

This project is based upon the Hitting the Headlines service of the National electronic Library for Health, and the Centre for Reviews and Dissemination, University of York