THC blood levels in impaired drivers increased 58% over a decade in Norway
Mean THC blood concentrations in drivers suspected of impaired driving in Norway increased 58% between 2000 and 2010, suggesting increased cannabis exposure from higher-potency products.
Quick Facts
What This Study Found
Researchers analyzed THC blood concentrations from 1,747 drivers apprehended in Norway on suspicion of driving under the influence of cannabis between 2000 and 2010. Mean THC concentrations increased from 4.0 ng/mL in 2000 to 6.6 ng/mL in 2010, a 58% increase over the decade.
For comparison, mean blood alcohol concentrations in impaired drivers increased only 3% over the same period, and amphetamine concentrations increased 16%. The disproportionate rise in THC levels suggested that cannabis users were being exposed to more THC, likely due to increasing potency of available cannabis products.
The increase in blood THC concentrations was partially paralleled by an increase in the percentage of drivers judged as lightly impaired by examining physicians.
Key Numbers
Mean THC blood concentration: 4.0 ng/mL (2000) to 6.6 ng/mL (2010), a 58% increase. Comparison: ethanol increased 3%, amphetamines increased 16%. Sample: 1,747 THC-only cases, 38,796 ethanol-only cases, 2,493 amphetamine-only cases.
How They Did This
Retrospective analysis of blood samples from drivers apprehended for suspected impaired driving in Norway between 2000 and 2010. Cases involving only THC (n=1,747) were compared to cases involving only ethanol (n=38,796) or amphetamines (n=2,493) to provide context for the THC trend.
Why This Research Matters
While cannabis potency has been documented to increase in many countries, this study was among the first to demonstrate that increased product potency translated into higher human exposure. Blood concentrations directly reflect what the body is actually absorbing, not just what the product contains.
The Bigger Picture
This study bridged two separate lines of evidence: rising cannabis potency and its real-world consequences. Knowing that THC content in cannabis products is increasing is important, but demonstrating that users are actually achieving higher blood levels confirms the public health relevance of potency trends.
What This Study Doesn't Tell Us
The sample consisted of drivers suspected of impairment, not a representative population of cannabis users. Users of higher-potency cannabis might be more likely to be apprehended. The study could not control for whether users adjusted their consumption in response to higher potency (e.g., smoking less). Norwegian cannabis markets may not reflect global trends.
Questions This Raises
- ?Have THC blood concentrations in impaired drivers continued to rise since 2010?
- ?Do higher blood THC levels translate directly to greater driving impairment?
- ?Are cannabis users in legal markets, where potency is labeled, better able to self-regulate their intake?
Trust & Context
- Key Stat:
- 58% increase in mean THC blood levels in impaired drivers over one decade
- Evidence Grade:
- Large observational dataset spanning a decade, though limited to a specific population of apprehended drivers.
- Study Age:
- Published in 2013 with data through 2010. Cannabis potency has continued to increase in many markets since then.
- Original Title:
- Has the intake of THC by cannabis users changed over the last decade? Evidence of increased exposure by analysis of blood THC concentrations in impaired drivers.
- Published In:
- Forensic science international, 226(1-3), 197-201 (2013)
- Authors:
- Vindenes, Vigdis(3), Strand, Dag Helge, Kristoffersen, Lena, Boix, Fernando, Mørland, Jørg
- Database ID:
- RTHC-00753
Evidence Hierarchy
Watches what happens naturally without intervening.
What do these levels mean? →Frequently Asked Questions
Are people getting more THC in their system than before?
This Norwegian study found that mean THC blood concentrations in suspected impaired drivers increased 58% from 2000 to 2010, suggesting that increased product potency is translating to higher human exposure.
Does higher-potency cannabis lead to worse driving impairment?
The study found a partial parallel between rising THC blood levels and the percentage of drivers judged as impaired, but the relationship between blood THC concentration and driving performance is complex and varies between individuals.
Read More on RethinkTHC
Cite This Study
https://rethinkthc.com/research/RTHC-00753APA
Vindenes, Vigdis; Strand, Dag Helge; Kristoffersen, Lena; Boix, Fernando; Mørland, Jørg. (2013). Has the intake of THC by cannabis users changed over the last decade? Evidence of increased exposure by analysis of blood THC concentrations in impaired drivers.. Forensic science international, 226(1-3), 197-201. https://doi.org/10.1016/j.forsciint.2013.01.017
MLA
Vindenes, Vigdis, et al. "Has the intake of THC by cannabis users changed over the last decade? Evidence of increased exposure by analysis of blood THC concentrations in impaired drivers.." Forensic science international, 2013. https://doi.org/10.1016/j.forsciint.2013.01.017
RethinkTHC
RethinkTHC Research Database. "Has the intake of THC by cannabis users changed over the las..." RTHC-00753. Retrieved from https://rethinkthc.com/research/vindenes-2013-has-the-intake-of
Access the Original Study
Study data sourced from PubMed, a service of the U.S. National Library of Medicine, National Institutes of Health.
This study breakdown was produced by the RethinkTHC research team. We analyze and report published research findings without making health recommendations. All interpretations are based solely on the published abstract and study data.