Objectives Priority reviews of new drug applications are resource intensive and drugs approved through this process have a greater likelihood of acquiring a serious safety warning compared to drugs approved through the standard process. Therefore, when Health Canada uses priority reviews, it is important that it accurately identifies products that represent a significant therapeutic advance. The purpose of this study is to compare Health Canada's use of priority reviews to therapeutic ratings from two independent organisations, the Patented Medicine Prices Review Board (PMPRB) and the French drug bulletin Prescrire International, over the period 1 January 1997–31 December 2012.

Design Cohort study.

Data sources Annual reports of the Therapeutic Products Directorate, and the Biologics and Genetic Therapies Directorate; evaluations of therapeutic innovation from PMPRB and Prescrire International; WHO Collaborating Centre for Drug Statistics Methodology.

Interventions Assessments by PMPRB and Prescrire International treated as a gold standard for postmarket therapeutic value.

Primary and secondary outcome measures Drug-by-drug comparison between the review status from Health Canada and the therapeutic status from PMPRB/Prescrire using κ values, and positive and negative predictive values. Analysis of the per cent of all new drug applications put into the priority review category over the 16-year period.

Results Health Canada approved 426 new drugs, and 345 were evaluated by PMPRB and/or Prescrire. 91 had a priority review and 52 were assessed as innovative (p=0.0003). Agreement between Health Canada and PMPRB/Prescrire was only fair (κ=0.330). The positive predictive value for Health Canada's review assignments was 36.3% and the negative predictive value was 92.5%.

Conclusions Health Canada's assignment of a priority approval to a new drug submission is only a fair predictor of the drug's therapeutic value once it is marketed. Health Canada should review its criteria for using priority reviews.