Table 2:

Co-Use domain recommendations

Level 1: Minimal burden to incorporate elements into data sets. Recommend the collection of multiple types of co-use; not just concurrent use, but also co-administration and sequential use. The goal of Level 1 assessments is to sufficiently capture those with varying patterns of co-use, with minimal added burden.
Cannabis metrics	Tobacco/nicotine metrics	Co-Use metrics
• Consumption metrics of cannabis (methods of use) • Frequency (days of use, times used per day, amount used per day) Timeframe: Ever (metrics collected when using) and past 12 months	• Consumption metrics of tobacco/nicotine use • Frequency (daily, near-daily, weekly, monthly) • Quantity of use (cigs/day, vaping episodes per day) Timeframe: Ever (metrics collected when using) and past 12 months	• Consumption metrics of co-administered products (blunts, spliffs) • Frequency of co-administered products • Patterns of co-use (sequential use, concurrent use) and temporal relations in use Assessment of concurrent co-use may also be derived from exclusive cannabis and tobacco metrics Timeframe: Ever and past 12 months
Level 2: Additional domains recommended to capture patterns of co-use, products used, and levels of dependence, quantity, frequency. This level allows for the assessment of associations between cannabis and tobacco use among co-users and should occur in addition to Level 1.
Cannabis metrics	Tobacco/nicotine metrics	Co-Use metrics
• Cannabis use methods: Combustible (joint/pipe/bong), vaporizer (dry herb/oil), edibles, dabbing/concentrates CBD • Potency: % THC, ratio of THC: CBD, strength of product • Dependence levels Timeframe: Past 12 months and past month	• Tobacco/nicotine use detailed methods: ENDS, smokeless, hookah • ENDS characteristics: nicotine concentration, flavors, type of device used • Dependence levels Timeframe: Past 12 months and past month	• Subjective effects of co-use • Substitution of products (during quit attempts, reduction, situations where one product cannot be used) • Changes in craving Timeframe: Past 12 months and past month
Level 3: Most comprehensive level and includes all measures from Levels 1 and 2, but also includes biochemical testing to determine levels of use for both tobacco/nicotine and cannabis, as well as toxicant exposure.
Cannabis metrics	Tobacco/nicotine metrics	Co-Use metrics
• Biochemical Assays: Biological samples to indicate use of substances (quantitative, if possible) • THC: 11-OH-THC, THC-COOH • CBD: 11-OH-CBD, CBD-COOH Timeframe: Subject to specific assays and times of detection	• Biochemical Assays: Biological samples to indicate use of substances (quantitative, if possible) • Cotinine • Total nicotine • Toxicant exposure Timeframe: Subject to specific assays and times of detection	• Event-level data: Ecologically-valid measures of co-use patterns (temporal relationships, impact on craving, substitution) • Relatedness: Assessment to capture the degree of relatedness (subjective effects, craving, shared triggers). Low relatedness suggests substances are used at different times; do not interfere with craving for the other substance and have few shared triggers. Timeframe: Past month