To assess the distribution and spending by cost-effectiveness category among those drugs with the highest public spending levels in Canada.

Repeated cross-sectional study.

The Canadian provinces of Manitoba, Ontario, New Brunswick, Nova Scotia, Prince Edward Island and Newfoundland.

Cost-effectiveness assessments by the Canadian Agency for Drugs and Technologies in Health (CADTH) for top-100 brand-name outpatient drugs by gross public plan spending in any year between 2015 and 2021 in Canada Institute for Health Information’s National Prescription Drug Utilization Information System data. Gross public plan spending by cost-effectiveness category.

From 2015 to 2021, 152 brand-name drugs occupied a top-100 rank and were included in the analysis. Of those, 117 had been assessed by CADTH. During the 7-year period, there was an increase in both top-100 drugs with cost-effective (from 18 to 24) and cost-ineffective (from 29 to 41) assessments, while drugs not assessed or with an unclear assessment declined (from 31 to 19 and from 22 to 16, respectively). As a share of spending on top-100 drugs with an assessment, spending on cost-effective drugs was mostly stable at 40%–46% from 2015 to 2021, while spending on cost-ineffective drugs increased from 30% to 45%.

A large and growing share of public drug spending has been allocated to cost-ineffective drugs in Canada. Dedicating large budgets to such treatments prevents spending with greater health impact elsewhere in the healthcare system and could restrain the capacity to pay for groundbreaking pharmaceutical innovation in the future.