New NIDA Study: THC Blood Levels Do Not Accurately Measure Intoxication
A new study from the National Institute on Drug Abuse has offered revealing information on the perceived correlation between cannabis consumption rates and THC blood concentration levels.
Researchers examined the blood and plasma levels of both frequent and occasional cannabis consumers, before and after smoking. Frequent and occasional smokers resided on a closed research unit and smoked one 6.8% THC cannabis cigarette. Blood and plasma cannabinoids were quantified on admission (approximately 19 hours before), 1 hour before, and up to 15 times (0.5–30 hours) after smoking.
The results showed that, “Cannabinoid blood and plasma concentrations were significantly higher in frequent smokers compared with occasional smokers at most time points for THC and 11-OH-THC and at all time points for THCCOOH and THCCOO-glucuronide.” Results were the same regardless of participants’ baseline concentration levels, or, how much THC was in their blood when the study began.
Researchers also found that the median time blood THC levels over 5 ng/ml were detectable was 3.5 hours in frequent smokers (ranging from 1.1 – 30 hours), and 1 hour in most occasional smokers (ranging from 0 – 2.1 hours); 2 individuals never tested over 5 ng/ml.
These results show a drastic difference in the amount time THC lingers in the blood of participants – not based on the amount of cannabis consumed, but on the frequency of their cannabis use.
This information is so important because many states in the U.S. have implemented drugged driving laws for cannabis based on a ng/ml level – including both Washington and Colorado, where recreational cannabis is now legal, and the standard measurement rendering a driver guilty of a cannabis DUI is 5 ng/ml.
The findings in this study indicate that people who consume cannabis more frequently are significantly more at-risk of being found guilty of a DUI, regardless of how long ago or how much they smoked, simply because THC lingers in their blood notably longer than those who consume cannabis occasionally or rarely.
Common sense and educated inference would indicate that a seasoned smoker would not, however, be rendered more intoxicated than a first-timer, or occasional smoker who consumed the same amount – therefore reaffirming the determination that intoxication from cannabis cannot be accurately measured by THC blood content.
The study, e-published ahead of print in the February issue of Clinical Chemistry, concludes by stating that, “Cannabis smoking history plays a major role in cannabinoid detection. These differences may impact clinical and impaired driving drug detection.”