Use of a catastrophic drug program, a last line of defence to protect people from drug expenses that can easily reach more than $10,000 a year, has soared in Ontario, a new study suggests.

The study's findings, published in Monday's CMAJ Open, reflect the pressure people face from rising drug costs and changing insurance coverage for workers, researchers say.

"We found that government spending for the catastrophic drug program in Ontario rose 840 per cent from 2000 to 2016," said Mina Tadrous, a research associate with the Ontario Drug Policy Research Network. "More importantly, there was a three-fold increase in the number of people who are relying on this program."

About three-quarters of Ontario residents are not covered by a public drug program and are eligible for the catastrophic drug program if they spend about three to four per cent of their after-tax household income on prescription medications.

As a pharmacist, Tadrous became interested in the topic as he observed more people coming in for prescription drugs with a price tag of more than $1,000 a month. Other researchers have said that in 2015 alone, more than 124 new drugs came on the market in that price range.

These drugs include biologics, lifelong treatments for rheumatoid arthritis (such as infliximab sold under the brand name Remicade) and Crohn's disease, HIV treatments and curative drugs for hepatitis C.

Tadrous speculated another factor that could be contributing to the increase in spending is a shift toward more younger, healthier adults turning to the program because they don't have the workplace coverage they need.

To conduct the study, the researchers looked at changes in patterns of use and government spending between 2000 and 2016 by analyzing Ontario databases stored at the Toronto-based Institute for Clinical Evaluative Sciences, where Tadrous is also a fellow at the institute.

They found the number of claimants increased from 37,436 to 128,166 over the study period.

The study's authors weren't able to determine the private insurance status and they just estimated household income of beneficiaries.

"I hope that this study draws more attention to the people who are sort of caught between the cracks falling between programs or not being able to get access as quickly as they should," Tadrous said. "And the second part [is] in any of the conversations ongoing that the impact of high-cost drugs is taken into account."

Under universal pharmacare, everyone would have drug coverage, not all drugs would be covered and programs like Ontario's catastrophic program would still exist.

Public drug plans end up shouldering the burden of expensive drugs that private plans aren't able to manage, said Marc-André Gagnon, an associate professor in the school of public policy and administration at Carleton University in Ottawa. He was not involved in the study.

"The role of a public plan is not to make private plans more sustainable. It's not to serve the commercial interests needs of private plans," Gagnon said. "It's about providing the best health outcomes for your population."

Gagnon said it would be better for public plans to negotiate the price of drugs from the start, have a national formulary and regulate who should have access to which drugs and under what conditions.