Canada is facing a major drug shortage problem and authorities must do more to notify patients when supplies of the medications they rely on are dwindling, as well as investigate the causes of the shortages, says the president of the Canadian Medical Association.

There are now more than 500 drugs listed on Health Canada's drug shortages website. Recent additions to the list include the anti-inflammatory drug Naproxen and the epilepsy drug Valproic Acid.

CMA President Dr. Louis Hugo Francescutti said the growing list is a major concern for patients whose health depends on regularly taking medication.

He said the addition of Valproic Acid, which is primarily used to treat children, is particularly concerning, given how sensitive epilepsy patients are to any change in medication.

"There should be great concerns, simply because people who live with epilepsy are pretty well walking on egg shells," he told CTV's Canada AM.

"If they find a medication that works well for them in controlling their seizures, it gives them the freedom to go on and do their daily activities."

He said the problem is that patients often aren't aware that a medication they rely on is in short supply until they reach the pharmacy to fill their prescription. This can lead to a "panic situation," he said, in which the patient must contact their doctor and scramble to arrange an appointment and find a substitution.

"And the replacement medication should not be started abruptly," Francescutti said. "For people living with epilepsy this is a major problem (and) potentially could lead to death as well."

He added that patients may also face additional costs if a generic drug is no longer available, but the brand-name version still is.

The latest additions to the drug shortages website highlight the scope of the drug shortage problem, he said, adding that Health Canada's reporting website does not adequately address the issue.

The drug shortages website, which was launched in 2012, often reports the problem too late and reporting is on a voluntary basis, which means the list isn't comprehensive, Francescutti said.

But it appears that Health Canada is taking steps to assess the issue. The agency recently launched a public consultation website, where Canadians can give feedback on the way drug shortages are reported.

The consultation site is accepting submissions until July 5. Canadians can also participate by downloading a PDF form and mailing it to Health Canada.

Francescutti said he hopes people will participate and share their stories so that the government is encouraged to act.

"If we get more Canadians to share their personal experience then hopefully the government will move to a solution, rather than right now (with) a website that reports the problem," he said.

"We need to figure out why we have these continual drug shortages. Having a website that tells us we have a drug shortage may help a little bit, but in the past two years we've noticed that nothing has really improved," he said.

Francescutti said the problem is so widespread that, at least once a shift in his emergency department, he gets a call from a pharmacist informing him that a previously available medication is no longer in stock. He said this causes costly delays, as he and his colleagues are forced to make additional calls and assessments.

"It's very inefficient, and for folks with epilepsy this could potentially be life-threatening," he said.