A panel of experts in the U.S. has determined that a decongestant found in many popular over-the-counter medications there and in Canada doesn't do anything to provide relief from a stuffy nose.
On Tuesday, advisers to the Food and Drug Administration (FDA) voted unanimously that phenylephrine is ineffective.
Here's a breakdown of that decision and what it could mean in Canada.
An independent panel for the FDA determined that phenylephrine was ineffective when taken in pill form.
The experts found that, when taken as a pill, only trace levels of the drug reach nasal passages to relieve congestion, rendering it ineffective.
The drug appears to work better when applied directly to the nose, whether by sprays or drops, and those products are not under review in the U.S.
If it doesn't work, how did it get so popular?
Phenylephrine became the main ingredient in over-the-counter decongestants in the U.S. after pseudoephedrine, another drug, was restricted because it can be used to make methamphetamine.
Phenylephrine is also found in many decongestants in Canada, including Nyquil, though pseudoephedrine is still found in others, such as Sudafed.
Over the years, numerous studies have questioned the benefits of phenylephrine, finding it no better than a placebo in trials.
The FDA advisory panel challenged the drug's effectiveness in 2007, but the regulator allowed the products to remain on the market pending additional research.
What do Canadian experts say?
Mina Tadrous, an assistant professor of pharmacy at the University of Toronto, says the panel's decision didn't come as a surprise.
"Phenylephrine is not considered to be that potent," he said.
"This is a very classic tale where you have drugs that have been approved since the '60s and '70s, and we're kind of just revisiting them now with the lens of data and analysis that we didn't use back then."
Cold medications containing pseudoephedrine were restricted in the U.S. because the drug can be used to make methamphetamine. (Paul Sancya/Associated Press)
The Canadian Paediatric Society called phenylephrine's use into question in 2011. Dr. Michael Rieder co-authored a statement outlining the group's position at that time.
"Our statement basically said: 'Common cold medications don't work, don't use them,'" said Rieder, a professor specializing in pediatric clinical pharmacology at Western University in London, Ont.
"There's no evidence that they work at all."
Phenylephrine carries minimal risk but such cold medications, he pointed out, can, of course, be expensive.
Rieder says there's also little evidence that pseudoephedrine is effective when ingested orally.
He notes decongestants also often contain acetaminophen, which can help alleviate the discomfort that comes with a cold. He recommends taking acetaminophen on its own, or another painkiller such as ibuprofen, for relief.
If this drug doesn't work, what does?
Given the wide range of options available, Tadrous recommends seeking help from your pharmacist.
Mina Tadrous, with the faculty of pharmacy at the University of Toronto, says phenylephrine is 'not considered to be that potent.' (Submitted by Mina Tadrous)
"The first person you should be talking to is your pharmacist and asking them, 'This is how I'm feeling, these are my symptoms. What is the best product for me?'"
Rieder, for his part, recommends people skip over-the-counter cough and cold medications altogether, and instead stay hydrated and rest up. A teaspoon of honey at night (for those over age one) a few times a day can also help, he says.
"We're in an age where people are less likely to suck it up," he said. "So many of these things just have to run their course."
In the U.S., there's unlikely to be any immediate impact from Tuesday's panel vote, according to The Associated Press.
The drug could eventually be removed from store shelves, but that would require the FDA to update what's permitted in over-the-counter medication.
Health Canada, which regulates drugs here, did not immediately provide comment.