potentially leading to unstable results. Fourth, while laboratory studies have provided the fundamental data identifying the cannabis withdrawal syndrome, it is possible that individuals willing to spend several days in an inpatient setting or to visit a laboratory every day for over a month may differ from the broader underlying population of frequent cannabis users in a manner that affects the study results.27 Without conducting research on cannabis withdrawal in a representative sample of frequent cannabis users, the extent to which sample biases have affected our understanding of cannabis withdrawal cannot be known. To our knowledge, such a study has never previously been conducted. Therefore, using data from a large, nationally representative survey that included frequent cannabis users, we investigated: (1) the prevalence of cannabis withdrawal symptoms; (2) their factor structure; (3) whether cannabis withdrawal is accompanied by significant distress or impairment, or use of another substance to relieve/avoid withdrawal (important indicators of clinical significance), and (4) the demographic characteristics, psychiatric and cannabis use history associated with cannabis withdrawal. We addressed these questions in two groups. The first included all frequent cannabis users in the survey (n=2,613), regardless of use of other substances. Results from this group maximized representativeness, but
