Does Starting to Smoke Cigars Trigger Onset of Cannabis Blunt Smoking?

Introduction: Among United States teens during the 1990s, increasing cigar use coincided with increasing use of tobacco cigar shells filled with cannabis, called "blunts." Cigar smokers are more likely to use cannabis, and we hypothesized that starting to smoke cigars might be a probabilistic "trigger" of blunt smoking. We turned to the case-crossover approach to evaluate this hypothesis. Methods: Within US National Surveys on Drug Use and Health, 2009-2013, we identified a nationally representative sample of newly incident blunt smokers aged 12- to 21-years-old (n = 4868) and compared month-of-onsets for smoking of cigars and blunts. Using the subjects-as-their-own-controls case-crossover design, we specified the first month prior to blunt use as a "hazard interval" and the second month prior to blunt use as a "control interval." We used Mantel-Haenszel (MH) estimators to estimate the matched-pairs odds ratio (OR). Results: The MH OR estimate was 1.7 (95% CI = 1.3, 2.3), with excess odds of cigar onsets during the hazard interval relative to the control interval. Two alternative control interval specifications yielded congruent estimates (OR = 2.7 and 2.9, respectively). Conclusions: A short interval right after starting to smoke cigars may be one of increased risk of starting to smoke blunts. We discuss cigar, cigarillo, and "blunt wraps" control approaches that might reduce both tobacco and cannabis-related harms. Implications: If this evidence is correct, increased market-targeting to promote youthful cigar and cigarillo smoking might be followed by increased rates of blunt smoking in a vulnerable population. As noted by others, enhanced risk of smoking-attributable harms might be a consequence of mixed tobacco-cannabis formulations.