New research appearing online today in Clinical Chemistry, the journal of AACC, shows that cannabis can be detected in the blood of daily smokers for a month after last intake. The scientific data in this paper by Bergamaschi et al. can provide real help in the public safety need for a drugged driving policy that reduces the number of drugged driving accidents on the road.
Cannabis is second only to alcohol for causing impaired driving and motor vehicle accidents. In 2009, 12.8% of young adults reported driving under the influence of illicit drugs and in the 2007 National Roadside Survey, more drivers tested positive for drugs than for alcohol. These cannabis smokers had a 10-fold increase in car crash injury compared with infrequent or nonusers after adjustment for blood alcohol concentration.
In this paper, 30 male chronic daily cannabis smokers resided on a secure research unit for up to 33 days, with daily blood collection. Twenty-seven of 30 participants were THC-positive on admission, with a median (range) concentration of 1.4 mcg/L (0.3–6.3). THC decreased gradually with only 1 of 11 participants negative at 26 days; 2 of 5 remained THC-positive (0.3 mcg/L) for 30 days.