@article{ref1,
title=""Residual blood THC levels in frequent cannabis users after over four hours of abstinence: a systematic review."",
journal="Drug and alcohol dependence",
year="2020",
author="Peng, Yuan Wei and Desapriya, Ediriweera and Chan, Herbert and Brubacher, Jeffrey R.",
volume="216",
number="",
pages="e108177-e108177",
abstract="BACKGROUND: Tetrahydrocannabinol (THC), the primary psychoactive component of cannabis, causes psychomotor impairment and puts drivers at increased risk of motor vehicle collisions. Many jurisdictions have per se limits for THC, often 2 or 5 ng/mL, that make it illegal to drive with THC above the &quot;legal limit&quot;. People who use cannabis regularly develop partial tolerance to some of its impairing effects. Regular cannabis users may also have persistent elevation of THC even after a period of abstinence. Some stakeholders worry that current per se limits may criminalize unimpaired drivers simply because they use cannabis. We conducted a systematic review of published literature to investigate residual blood THC concentrations in frequent cannabis users after a period of abstinence.   METHODS: We identified relevant articles by combining terms for &quot;cannabis&quot; and &quot;blood&quot; and &quot;concentration&quot; and &quot;abstinence&quot; and searching MEDLINE, EMBASE, PsycINFO, and Web of Science. We included studies that reported THC levels in frequent cannabis users after more than 4 h of abstinence.   RESULTS: Our search identified 1612 articles of which 8 met our inclusion criteria. After accounting for duplicate publications, we had identified 6 independent studies. These studies show that blood THC over 2 ng/mL does do not necessarily indicate recent cannabis use in frequent cannabis users. Five studies reported blood THC >2 ng/mL (or plasma THC >3 ng/mL) in some participants after six days of abstinence and two reported participants with blood THC >5 ng/mL (or plasma THC > 7.5 ng/mL) after a day of abstinence.   CONCLUSIONS: Blood THC >2 ng/mL, and possibly even THC >5 ng/mL, does not necessarily represent recent use of cannabis in frequent cannabis users.  Keywords : Cannabis impaired driving <p /> <p>Language: en</p>",
language="en",
issn="0376-8716",
doi="10.1016/j.drugalcdep.2020.108177",
url="http://dx.doi.org/10.1016/j.drugalcdep.2020.108177"
}