Cannabis, Other Illicit Drugs, Associated With “Small Or Moderate Increases In Accident Risk,” Study Says

Oslo, Norway: The use of cannabis as well as various other illicit substances, poses a "small or moderate increase in accident risk," according to a systematic review and meta-analysis of studies published online in the journal Accident Analysis and Prevention.

An investigator from Aalborg University and the Institute of Transport Economics in Oslo assessed the risk of road accident associated with drivers’ use of licit and illicit drugs, including amphetamines, analgesics, anti-asthmatics, anti-depressives, anti-histamines, benzodiazepines, cannabis, cocaine, opiates, penicillin and zopiclone (a sleeping pill). The author reviewed data from 66 separate studies evaluating the use of illicit or prescribed drugs on accident risk.

After the author adjusted for publication bias (editors’ tendency not to publish studies that fail to show significant risks), the study found that cannabis was associated with minor, but not significantly increased odds of traffic injury (1.06) or fatal accident (1.25).

By comparison, opiates (1.44), benzodiazepine tranquillizers (2.30), anti-depressants (1.32), cocaine (2.96), amphetamines (4.46), and the sleeping aid zopiclone (2.60) were all associated with a greater risk of fatal accident than cannabis. Anti-histamines (1.12) and penicillin (1.12) were associated with comparable odds to cannabis.

The study concluded: "By and large, the increase in the risk of accident involvement associated with the use of drugs must be regarded as modest. … Compared to the huge increase in accident risk associated with alcohol, as well as the high accident rate among young drivers, the increases in risk associated with the use of drugs are surprisingly small."

By contrast, separate experimental data indicates the combined ingestion of cannabis and alcohol can likely increase crash risk in a manner that is greater than that associated with the use of either substance alone.

For more information, please contact Paul Armentano, NORML Deputy Director, at: Full text of the study, "Risk of road accident associated with the use of drugs: A systematic review and meta-analysis of evidence from epidemiological studies," appears in the journal Accident Analysis and Prevention. Additional information regarding cannabis use and psychomotor behavior is available in the NORML white paper, "Cannabis and Driving: A Scientific and Rational Review," available online at: