"I think it would alarm a lot of Canadians if they knew that there isn't a lot of study on this," said Phil Emberley, director of pharmacy innovation at the Canadian Pharmacists Association.
Drug manufacturers must provide evidence on the potency and safety of products related to exposure to light, heat and humidity in order to get market approval from Health Canada, using what are known as stability studies.
"The purpose of the stability study is to establish, based on testing a minimum of three batches of the drug product, a shelf life and label storage instructions applicable to all future batches of the drug product manufactured and packaged under similar circumstances," Health Canada says.
These tests include studies in which pilot batches of medications are stored at a temperature of about 25 C, with about 60 per cent relative humidity, for a minimum of 12 months, the federal department says on its website.
The expiration date is the final date that a manufacturer will guarantee 100 per cent potency and safety of a medication, based on stability testing under Health Canada's good manufacturing practices, or GMP.
But that best-before date is based on an unopened container. Once a dispensing pharmacist or patient has opened a bottle or package, exposing the contents to the elements, manufacturers no longer consider original expiry dates in force, Emberley said.
"So if you have a bottle that, say, expires in five years, as soon as it's opened, technically it expires in less than five years," he said. "A lot of people keep their medications in their bathrooms where they're exposed to heat and humidity, and there is evidence to suggest that it speeds up the degradation process."
He said it's in manufacturers' best interest to be somewhat conservative in choosing best-before dates "because they could face legal liability if it's shown that these products expire sooner than later."
"And also it allows them to sell more product as product expires and people need to replenish what they have."
However, the few long-term studies that have been done on the long-term viability of medications suggest the shelf life of some drugs may be much longer than their use-by dates indicate.
One study by the Food and Drug Administration was conducted at the behest of the U.S. military, which wanted to determine if its large and costly stockpile of OTC and prescription medications were still usable. After assessing more than 100 drugs, the FDA found that almost 90 per cent were still effective well after their expiration dates, some as long as 15 years later.
Still, Emberley said best-before dates shouldn't be taken lightly.
In the case of Alesse 21, the pills were sold in western Canada in March and April, but carried an expiry date of last September. It's not known if women who took these oral contraceptives received a fully potent dose or whether they are at risk for unwanted pregnancy.
Other prescription drugs could also lack effectiveness if the expiration date has gone by, and some could be potentially harmful. For example, taking out-of-date nitroglycerin, used to treat angina, could have severe repercussions if potency has waned, Emberley said.
Insulin for diabetes and autoinjected epinephrine for anaphylactic shock are another two drugs known to lose their potency beyond their expiration dates.
Suggesting it's better to be safe than sorry, Emberley advises consumers to cull any out-of-date drugs from their medicine cabinets and take them to a pharmacy to be destroyed.
Dr. David Juurlink, head of clinical pharmacology and toxicology at Sunnybrook Health Sciences Centre in Toronto, said concerns about diminished potency depends on the drug and how much time has elapsed since the best-before date.
"For most drugs, the passage of a short amount of time after the expiry date is really of little clinical consequence," he said. "In general, something that's six to 12 months past the expiry date, with rare exceptions, is not going to be a problem at all. They're not going to be dangerous."
A 2012 study of a small number of drugs — some of them bottled or packaged 40 years earlier — found that active ingredients did degrade over time, but some more than others. For instance, researchers found ASA pills dropped in strength from 200 milligrams to two milligrams, while codeine barely lost any of its chemical constituents.
"It's not like milk, and it's not as though something magical happened on the expiry date and the drug loses all of its potency," Juurlink said. "With most, but not all, it's probably safe to take drugs that have expired recently. But the more time that has elapsed from the expiry date, the less advisable it becomes."
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