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Comment & Response
October 27, 2015

Medical Use of Cannabinoids—Reply

Author Affiliations
  • 1University of Bristol, Bristol, England
  • 2Kleijnen Systematic Reviews, York, England
JAMA. 2015;314(16):1751-1752. doi:10.1001/jama.2015.11447

In Reply Dr Grant suggests that we only included 1 of the 5 studies conducted by the University of California Center for Medicinal Cannabis Research. However, all 5 studies were included in our review, and full details of their results are listed in our web appendices.

Four of the studies were not included in our primary analyses because they used a crossover design. As highlighted in the discussion section of our review, a potential problem with randomized trials using crossover designs is the possible unblinding due to strong treatment or adverse effects. In addition, studies of this design were rarely analyzed appropriately, and none reported the required data accounting for their crossover design to permit appropriate inclusion in meta-analyses. Therefore, the primary analyses were based only on parallel-group studies, and crossover trials were included for the sensitivity analyses.