The findings, based on the 2007 Canada Community Health Survey, are reported in the Canadian Medical Association Journal.
People who were in poor health, who had lower incomes and who lived in British Columbia were more likely to report not taking or sticking with prescribed drugs because of the cost.
The phenomenon was particularly noticeable among people without drug insurance; one in four of these respondents said they could not afford to have their prescriptions filled.
Those under the age of 65 were also less likely to take medication as prescribed for cost reasons.
The study was done by researchers at the University of British Columbia, the University of Toronto and the Institute for Clinical Evaluative Sciences in Toronto.
The survey polled more than 5,700 people across Canada.
The authors suggested the problem has an impact on the health of the individuals and the overall cost of their care.
"Reducing cost-related non-adherence would likely improve health and reduce spending in other areas, such as admissions to hospital for acute care," they wrote in their conclusion.
"Of all the factors we found to be associated with cost-related non-adherence, insurance coverage is the most amenable to being addressed through changes in public policy."
Dr. Michael Law of the Centre for Health Services and Policy Research at UBC, said the findings are timely with premiers meeting this week in Victoria.
"The country's 13 provincial and territorial premiers should focus on how to address this disparity to improve access to prescription drugs for all Canadians," he said in a release.
About two-thirds of Canadian households incur out-of-pocket expenses for prescription drugs each year because they don't have a private or public insurance drug plan, the study noted.
Their payments amounted to about $4.6 billion in 2010, or about 17.5 per cent of total spending on prescription drugs, the authors said.