Urinary Δ⁹-tetrahydrocannabinol and metabolite concentrations following cannabis use: A systematic review

Urine testing is used in a variety of contexts to identify cannabis use. Most tests target 11-nor-9-carboxy-Δ⁹-tetrahydrocannabinol (11-COOH-THC), the terminal metabolite of Δ⁹-tetrahydrocannabinol (THC), the principal intoxicant in cannabis. Different authorities use different threshold concentrations to define a positive test. This systematic review synthesised the urinary THC and THC-metabolite concentrations reported in prior studies involving administration of cannabis/cannabis-based products (acute and repeated dosing) and users of such products (during use and extended abstinence). The overall objectives were to: (1) clarify how different use patterns affect these concentrations; and (2) contextualise the thresholds applied in key contexts - specifically, workplaces (and workplace-aligned contexts, e.g., criminal justice) and competitive sport. Ninety-two eligible studies were identified and included. Typical workplace threshold (15 ng/mL total 11-COOH-THC): Low single doses (i.e., 1.0-5.0 mg) and very low repeated doses (i.e., <1.0 mg/day) of THC were sometimes sufficient to exceed the workplace threshold, particularly with oral ingestion. Weekly to daily cannabis users could remain above this threshold for weeks following cessation. World Anti-Doping Agency (WADA) Decision Limit (180 ng/mL total 11-COOH-THC): Low-to-moderate oral doses (i.e., 10 mg) and moderate inhaled doses (i.e., 15-20 mg) of THC were sometimes sufficient to exceed the WADA Decision Limit, as was weekly cannabis use. Weekly to daily cannabis users often fell below this threshold within a week of cessation, although heavy users took longer. This synthesis may assist policymakers in selecting appropriate urine-testing thresholds and in educating individuals about the risks of testing positive following different patterns of cannabis use.