Health Effects of High-Concentration Cannabis Products: Scoping Review and Evidence Map

Abstract

Background. The concentration of pharmacologically active tetrahydrocannabinol (THC) in cannabis products has been increasing over the past decade. Concerns about potential harmful health effects of using these increasingly higher-concentration products have led some states to consider regulation of cannabis product THC concentration. We conducted a scoping review of health effects of high-concentration cannabis products to inform policy on whether the THC concentrations of cannabis product should be regulated or limited. Objectives. We conducted a scoping review to (1) identify and describe human studies that explore the relationship of high-concentration cannabis products with any health outcomes in the literature and (2) create an interactive evidence map of the included studies to facilitate further analyses. Search Methods. An experienced medical information specialist designed a comprehensive search strategy of 7 electronic databases. Selection Criteria. We included human studies of any epidemiological design with no restrictions by age, sex, health status, country, or outcome measured that reported THC concentration or included a known high-concentration cannabis product. Data Collection and Analysis. We imported search results into Distiller SR, and trained coders conducted artificial intelligence‒assisted screening. We developed, piloted, and revised data abstraction forms. One person performed data abstraction, and a senior reviewer verified a subset. We provide a tabular description of study characteristics, including exposures and outcomes measured, for each included study. We interrogated the evidence map published in Tableau to answer specific questions and provide the results as text and visual displays. Main Results. We included 452 studies in the scoping review and evidence map. There was incomplete reporting of exposure characteristics including THC concentration, duration and frequency of use, and products used. The evidence map shows considerable heterogeneity among studies in exposures, outcomes, and populations studied. A limited number of reports provided data that would facilitate further quantitative synthesis of the results across studies. Conclusions. This scoping review and evidence map support strong conclusions concerning the utility of the literature for characterizing risks and benefits of the current cannabis marketplace and the research approaches followed in the studies identified. Relevance of the studies to today's products is limited. Public Health Implications. High-quality evidence to address the policy question of whether the THC concentration of cannabis products should be regulated is scarce. The publicly available interactive evidence map is a timely resource for other entities concerned with burgeoning access to high-concentration cannabis. (Am J Public Health. 2023;113(12):1332-1342. https://doi.org/10.2105/AJPH.2023.307414).

FIGURE 1—

PRISMA Diagram for Study Identification for Health Effects of High-Concentration Cannabis Products: Scoping Review and Evidence Map Note. PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-analyses; THC = tetrahydrocannabinol.

FIGURE 2—

Number of Studies With Reported THC Concentration, Frequency, or Duration of Cannabis Use by Cannabis Product Type in Health Effects of High-Concentration Cannabis Products: Scoping Review and Evidence Map Note. THC = tetrahydrocannabinol. Counts indicate the number of studies with an included cannabis product type and cannabis exposure characteristic. Studies may include multiple product types and exposures. Color saturation indicates the number of studies with a reported product or exposure in relation to other product or exposures. Total n = 446 because 6 studies reported that they tested a high-concentration product but did not report numeric THC concentration, frequency, or duration.

FIGURE 3—

THC Concentration Reported as Percentage of THC and Milligrams of THC by Outcome Domain in Health Effects of High-Concentration Cannabis Products: Scoping Review and Evidence Map Note. IQR = interquartile range; THC = tetrahydrocannabinol. Boxplot of highest reported THC concentration for concentrations reported in % THC (n = 172) or mg THC (n = 113) by outcome domain. We report data on THC concentration reported as an exact concentration (e.g., 10% THC), a range (e.g., 1–10 mg THC), a threshold (e.g., < 5% THC), or some other method of aggregation (e.g., mean % THC). THC concentration values were not standardized. The midline of the box is the median THC concentration, the top and bottom of the box are first and third quartile (Q1 and Q3), whiskers represent the Q1‒1.5(IQR) and Q3 + 1.5(IQR), and points beyond the whiskers are outliers beyond this range.