Objective: The availability of cannabis in Norway seems to have increased according to seizures by customs and police. On the other hand, national population surveys have not found any increase in self-reported use of cannabis. This investigation aimed at studying trends in cannabis use among suspected drug-impaired drivers apprehended by the police in Norway.
Methods: A time series observational study of cannabis use among all drivers tested for drugs during 2000-2015 was performed. Descriptive analyses of trends in frequencies and combined use of cannabis with other drugs or alcohol for different age groups and gender were conducted.
Results: Tetrahydrocannabinol (THC) is the main psychoactive substance in cannabis and was detected in blood samples from 18,767 suspected drug-impaired drivers. The annual number of THC findings increased during the years 2000-2015 for all age groups. For cannabis-only users, young drivers aged 20-29 years dominated during the whole period, whereas for multidrug-cannabis users the median age increased steadily during 2000-2015. After 2009, the annual increase in THC findings escalated; THC-only findings increased the most.
Conclusions: Increasing numbers of THC-positive drivers were found among all age groups and genders; the strongest trend was observed between 2009-2015 for young drivers testing positive only for THC.
Keywords: Cannabis; THC; driving under the influence; high-risk drug users; trends.