Summary of Cannabis Claims Review Methodology

Selection of Claims:

  • Initial selection of the primary “claims” involved review of articles and news stories related to cannabis that Dr. Dan Werb (DW) and colleagues had located and shared. Dr. Tara Marie Watson (TMW) checked additional links and references, if any, included in these materials. TMW read all material on the Smart Approaches to Marijuana (SAM) websites (U.S. and Canadian versions). Notes were taken and included relevant or interesting quotes/excerpts.

  • DW and TMW met in January and early February 2015 to discuss a preliminary list of claims – this list was narrowed down after discussion and consensus was reached. Final list included 13 claims (7 related to cannabis use, 6 related to cannabis regulation).

 Common Claims on Cannabis Use

  1. “Cannabis [is] as addictive as heroin.”
  2. “[D]id you know that marijuana is on average 300 to 400 percent stronger than it was thirty years ago?”
  3. “I’m opposed to legalizing marijuana because it acts as a gateway drug.”
  4. Cannabis use “can cause potentially lethal damage to the heart and arteries.”
  5. Cannabis use lowers IQ by up to 8 points.
  6. Cannabis use impairs cognitive function.
  7.  “[Cannabis] is a drug that can result [in] serious, long-term consequences, like schizophrenia.” 

Common Claims on Cannabis Regulation

  1. Legalization / regulation increases the availability of cannabis.
  2. “[I]f marijuana was legalized, the increase in users would be both large and rapid…”
  3. Regulation will not reduce drug crime.
  4. “We are going to have a lot more people stoned on the highway and there will be consequences.”
  5. Regulation promotes drug tourism.
  6. Regulation leads to a “Big Marijuana” scenario.

Academic Databases Searched Between January and March 2015:

  • Scopus
  • MEDLINE searches - Ovid MEDLINE(R) without Revisions; PsycINFO; Embase
  • Sociological Abstracts

*Note: TMW also SEARCHED CINAHL at first, but it did not turn up unique articles.

  • Keywords searches always included “cannabis” and “mari*”; other keywords specific to particular claims included: addicti*; dependen*; gateway; poten*; IQ; intelligen*; cogniti*; health; cardio*; pulmon* or respirat*; schizophreni*; legaliza*; regulat*; impaired driv*; touris*; industry

  • Refworks was used to store and organize citations and abstracts; TMW de-duplicated citations after performing searches and read through all remaining titles to retain those that appeared relevant.

Review/Narrative Synthesis of Evidence:

  • TMW proceeded claim by claim, starting with the 7 claims related to cannabis usage. Published reviews of evidence were prioritized, where available – these varied in terms of type/quality. Original research articles were retrieved, and located key articles that were mentioned in reviews.

  • Initially tried to modify and use a checklist for appraising the quality of studies found in Downs and Black (1998), but this was more specific to intervention studies and we had not decided whether we would try to use any criteria to appraise reviews. Loosely used criteria when reading original articles, including: clear description of hypothesis, if applicable?; possible confounders? explanation of confounders?; clear description of methods?; sample size; evaluation or follow-up of participants?

  • A table was prepared that contained beside each claim: a very brief summary; snapshot of supporting evidence with key references; snapshot of opposing evidence with key references; and strength of the evidence (i.e., weak, moderate, strong). Write-ups for each claim started with a longer evidence summary which was then distilled further into a short summary (note: TMW aimed for plain language with the short summaries). DW reviewed all write-ups, DW and TMW met to discuss the summaries, and these were revised. Finally, Ms. Nazlee Maghsoudi (NM) reviewed all drafts for clarity and ensured that all summaries were suited to key audiences (policymakers, general public, advocacy organizations).

  • All materials were externally peer-reviewed by experts in the field of cannabis regulation and use (Mr. Steve Rolles and Mr. George Murkin, Transform Drug Policy Foundation) for veracity and relevance.

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