Self-report methodology for quantifying standardized cannabis consumption in milligrams delta-9-tetrahydrocannabinol

<i>Background:</i> There is currently no format-independent method to determine delta-9-tetrahydrocannabinol (THC) in milligrams for self-report studies. <i>Objectives:</i> Validate self-report method for quantifying mg THC from commercially available cannabis products using product labeling, which includes both net weight and product potency. <i>Methods:</i> 53 adult cannabis users (24 M, 29F), 21–39 years of age (<i>M</i> = 28.38, SD = 4.15), were instructed to report daily use via a weekly survey for two consecutive weeks, provide product label photographs, abstain from use for 24 h, submit a urine sample and complete the Cannabis Use Disorder Identification Test – Revised (CUDIT-R) and the Marijuana Craving Questionnaire – Short Form (MCQ-SF). Milligrams of THC were determined by multiplying quantity of product used by its THC concentration. Urine was analyzed for the urine metabolite 11-nor-carboxy-THC (THC-COOH) via liquid chromatography mass spectroscopy. THC and THC-COOH values were log10 transformed prior to correlational analyses. <i>Results:</i> Median daily THC consumption was 102.53 mg (<i>M</i> = 203.68, SD = 268.13). Thirty-three (62%) of the 53 participants reported using two or more formats over the 2-week period. There was a significant positive correlation between log10 THC-COOH and log10 THC mg (r(41) = .59, <i>p</i> &lt; .001), log10 THC mg and MCQ-SF score (r(41) = .59, <i>p</i> &lt; .001), and log10 THC mg dose and CUDIT-R score, (r(41) = .39, <i>p</i> = .010). <i>Conclusion:</i> Our label-based methodology provides consumption information across all modalities of cannabis use in standard units that can be combined across products for calculation of dose. It is a viable and valid method for quantifying mg of THC consumed and can be utilized in any region where cannabis is legal, and labeling is regulated.