Is cannabis dangerous? A review of research over the last 20 years ...

From commentary in The Independent
7.10.14

"A newly published paper reminds health professionals, policy makers, and the public, of the potential acute and long-term risks of cannabis use. 

In his report, Professor Wayne Hall at The University of Queensland Centre for Youth Substance Abuse Research, considers how the evidence has evolved over the past 20 years. He points out potential risks, both in the short term, and higher risks for three settings: long-term heavy use, use in adolescence, and during pregnancy."

With acute use, risks of cannabis include psychological effects – some people have an unpleasant dysphoric rather than euphoric response – and impaired concentration and coordination, with risk of road and other accidents, enhanced in the presence of alcohol or other drugs. Risks from exposure during pregnancy include reduced birth weight and impaired post-natal educational development, at least until adolescence. Risks of sustained use from adolescence also include impaired intellectual development. Other reported adverse effects of long-term use of cannabis include dependence, the risk higher in those who start in adolescence, and an increased risk of psychotic symptoms, especially in those with a family history of psychotic disorders or those who start young.  Regular use in older adults increases the risk of heart attack and chronic bronchitis. Cardiovascular and respiratory risks of cannabis are increased by concomitant tobacco use.

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Anti-depressants, benzodiazepines, newer sleeping medicines and risk of motor accidents?

@HealthMed: The following comments were in response to a new paper linking use of anti-depressants, benzodiazepines and newer sleeping medicines to increased risk of motor vehicle accidents.

These comments were part of the briefing on this paper from the Science Media Centre.

In a paper published in the British Journal of Clinical Pharmacology, Tsai and colleagues from Taiwan have reported a ~40-70% relative increase in risk of non-fatal driving accidents in Taiwan linked to prescription of a wide range of anti-depressants, benzodiazepines and newer Z-drug sleeping medicines. In their study, around 5200 people who had had motor accidents were compared with around 31,000 people with no history of accidents. The medicines appeared possibly linked to from 1 in 20, to 1 in 70 accidents, depending on the drug type. Obvious questions for pharmacologists, health professionals and the public are whether these findings are credible, and if so, generalisable to other parts of the world.

This Taiwan report was based on a case-control study – more open to bias than randomized trials. Although the researchers matched controls for age, gender and year of the accidents, they were unable to rule out differences in patterns of driving or in alcohol intake between the groups. Alcohol amplifies any impairment in concentration resulting from effects of drugs that act on the brain; and ethnic Taiwanese are commonly are intolerant of alcohol, due to genetic lack of the enzyme needed to break down alcohol.

It is also possible that the increased accident risk resulted from effects of underlying psychological or psychiatric disorders for which the drugs were prescribed e.g. through poorer concentration or indirectly through additional effects of sleep disturbance caused by the conditions under treatment, independent of the drugs. In addition the researchers noted that those who had accidents also had a higher burden of a range of non-psychiatric diseases, also recognized as increasing risk of accidents.

What do these results mean for populations in other countries? Several of the drugs implicated in Taiwan are not commonly used in other countries and there are several sources of bias indicating need for caution in interpreting the study. However other studies have stressed the need for caution when driving when using these types drugs. When these drugs are prescribed, patients should seek advice about risks of driving from their physician or pharmacist. In any event, patients on these drugs should avoid any alcohol when driving.

More information: Chia-Ming Chang and colleagues. Psychotropic Drugs and Risk of Motor Vehicle Accidents: a Population-based Case-Control Study; British Journal of Clinical Pharmacology; DOI: 10.1111/j.1365-2125.2012.04410.x

Prevalence of alcohol and other drugs in fatally injured drivers. Joanne E. Brady, Guohua Li.  Addiction. Published online August 20, 2012