Drugged driving
===============

* Laurence Jerome

In a *CMAJ* news article1 Wanniarachige states that it is difficult to establish a dose–effect response between cannabis use and driving risk. A review of the literature by Ramaekers and colleagues2 concludes that the “degree of performance impairment observed in experimental studies after doses up to 300 μg/kg THC [tetrahydrocannabinol] were equivalent to the impairing effect of an alcohol dose producing a blood alcohol concentration ≥ 0.05 g/dl, the legal limit for driving under the influence in most European countries.”2 Ramaekers and colleagues note that “[s]ignificant performance impairment emerges at serum THC concentrations > 2 ng/ml and crash risk significantly increases at serum THC concentrations between 4–10 ng/ml.”2 They observe that “combined use of THC and alcohol produces severe driving impairment and sharply increases the risk of drivers’ accident culpability as compared to drug-free drivers even at low doses.”2

![Figure1](http://www.cmaj.ca/https://www.cmaj.ca/content/cmaj/187/9/681.1/F1.medium.gif)

[Figure1](http://www.cmaj.ca/content/187/9/681.1/F1)

Image courtesy of Deirdre Rusk/iStock

A link exists between attention-deficit/hyperactivity disorder (ADHD) and driving risk.3 The Dunedin study presents data on the effects of chronic frequent cannabis use starting in the teen years, showing toxic effects on cognitive neurodevelopment, which produce irreversible clinical syndromes indistinguishable from ADHD, and apparently irreversible loss of IQ, even after discontinuation of cannabis.4 This merits careful study by those advising legislators about the risks of intoxicated driving.

## References

1.  Wanniarachige D. Drugged-driving: putting the brakes on pot use. CMAJ 2015;187:315.
    
    [FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiRlVMTCI7czoxMToiam91cm5hbENvZGUiO3M6NDoiY21haiI7czo1OiJyZXNpZCI7czo5OiIxODcvNS8zMTUiO3M6NDoiYXRvbSI7czoyMjoiL2NtYWovMTg3LzkvNjgxLjEuYXRvbSI7fXM6ODoiZnJhZ21lbnQiO3M6MDoiIjt9) 

2.  Ramaekers JG, Berghaus G, van Laar MW, et al. Dose related risk of motor vehicle crashes after cannabis use: an update. Drug Alcohol Depend 2004;73:109–19.
    
    [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.1016/j.drugalcdep.2003.10.008&link_type=DOI) 
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=14725950&link_type=MED&atom=%2Fcmaj%2F187%2F9%2F681.1.atom) 
    
    [Web of Science](http://www.cmaj.ca/lookup/external-ref?access_num=000188508500001&link_type=ISI) 

3.  Jerome L, Segal A, Habinski L, et al. What we know about ADHD and driving risk: a literature review. J Can Acad Child Adolesc Psychiatry 2006;15:105–25.
    
    [CrossRef](http://www.cmaj.ca/lookup/external-ref?access_num=10.1007/s00787-006-0506-y&link_type=DOI) 
    
    [PubMed](http://www.cmaj.ca/lookup/external-ref?access_num=18392181&link_type=MED&atom=%2Fcmaj%2F187%2F9%2F681.1.atom) 
    
    [Web of Science](http://www.cmaj.ca/lookup/external-ref?access_num=000235886700006&link_type=ISI) 

4.  Meier MH, Caspi A, Ambler A, et al. Persistent cannabis users show neuropsychological decline from childhood to midlife. Proc Natl Acad Sci USA 2012;109:E2657–64
    
    [Abstract/FREE Full Text](http://www.cmaj.ca/lookup/ijlink/YTozOntzOjQ6InBhdGgiO3M6MTQ6Ii9sb29rdXAvaWpsaW5rIjtzOjU6InF1ZXJ5IjthOjQ6e3M6ODoibGlua1R5cGUiO3M6NDoiQUJTVCI7czoxMToiam91cm5hbENvZGUiO3M6NDoicG5hcyI7czo1OiJyZXNpZCI7czoxMjoiMTA5LzQwL0UyNjU3IjtzOjQ6ImF0b20iO3M6MjI6Ii9jbWFqLzE4Ny85LzY4MS4xLmF0b20iO31zOjg6ImZyYWdtZW50IjtzOjA6IiI7fQ==)