THC Metabolites Remain in Blood for Extended Periods During Abstinence

According to data recently published in the journal Drug and Alcohol Dependence, THC remained detectable in blood at levels greater than 2.0 ng/ml during several days of abstinence.

Investigators affiliated with the University of British Columbia reviewed the relevant literature assessing residual THC plasma levels in those who regularly consume cannabis.  They reported: “[I]n all studies where participants were observed for over a day, blood THC [levels] in some participants remained detectable during several days of abstinence,” with some subjects continuing to test positive for up to 30 days. Some subjects also demonstrated a so-called “double hump” pattern “where their THC levels rose toward the end of the week after an initial decline.”

The authors concluded, “The studies in our review consistently demonstrate that positive blood THC levels, even levels over 2 ng/ml, do not necessarily indicate recent cannabis use in frequent cannabis users.”

The study’s findings should have implications for Iowa’s zero-tolerance per se law that criminalizes the operation of a vehicle by a driver solely based upon the detection of trace levels (“any amount”) of even non-impairing THC metabolites in blood or urine.

THC in blood, especially at low levels, is not a consistent predictor of either recent use or impairment of performance.

In this era of “follow the science” for masks and social distancing to combat the spread of COVID-19, the state would be wise to revisit the “any amount” threshold under Iowa Code chapter 321J and end the backdoor prohibition of cannabis for OWI.