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Aims  To investigate the relationship between marijuana use prior to driving, habitual marijuana use and car crash injury

Design and setting  Population based case–control study in Auckland, New Zealand.

Participants  Case vehicles were all cars involved in crashes in which at least one occupant was hospitalized or killed anywhere in the Auckland region, and control vehicles were a random sample of cars driving on Auckland roads. The drivers of 571 case and 588 control vehicles completed a structured interview.

Measurements  Self reported marijuana use in the 3 hours prior to the crash/survey and habitual marijuana use over the previous 12 months were recorded, along with a range of other variables potentially related to crash risk. The main outcome measure was hospitalization or death of a vehicle occupant due to car crash injury.

Findings  Acute marijuana use was significantly associated with car …