With cold and flu season ramping up, you may soon be heading to the pharmacy in search of relief. When you do, you might remember that Sudafed has long been considered an effective decongestant. So you grab a box of oral decongestant that says Sudafed. You may or may not notice that the brand name is now followed by two letters: PE.

But Sudafed PE is a completely different drug from the original Sudafed, which can only be purchased from behind the counter. Other oral decongestants on drugstore shelves are very likely to be made with the same ingredient as Sudafed PE — phenylephrine. And it’s not effective. A few weeks ago, an FDA advisory panel confirmed what some patients, pharmacists and doctors have long suspected: that oral decongestants based on phenylephrine don’t decongest.

Decongestant pills with phenylephrine are so ubiquitous and so cleverly packaged that they were worth about $1.8 billion in sales last year. And they aren’t the only over-the-counter product that doesn’t work as advertised, said Leslie Hendeles, an emeritus pharmacy professor at the University of Florida. Consumers scanning pharmacy shelves must sort through ineffective cough medicines, anti-itch creams and medications for gastrointestinal complaints. There are also an array of dubious homeopathic remedies, which can be sold despite the fact that none are FDA-approved.

The situation is particularly confusing in the cold, flu and allergy aisle because most oral decongestants used to be effective. In the 2000s they were quietly replaced by products with phenylephrine.

Back in the 1990s, Hendeles said, there was only one oral decongestant based on phenylephrine, and he wrote a paper in 1993 arguing that it was unlikely to work. The problem was that it didn’t get into the bloodstream. More than 99% was broken down in the digestive tract and liver. (Nasal sprays, by contrast, are effective).

But this attracted little attention at the time because most of the products on the cold, flu and allergy aisle were made with highly effective decongestants — pseudoephedrine or phenylpropanolamine.

But shortly after the turn of the millennium, drugs based on these ingredients became harder to get. Drugs with phenylpropanolamine were taken off the market because it was associated with hemorrhagic strokes when used in much higher doses in a weight-loss drug called Dexatrim. And pseudoephedrine was being used to create illegal methamphetamine. In 2005, Congress passed the Combat Methamphetamine Epidemic Act, after which consumers in search of Sudafed had to show a picture ID and be logged into a database that would prevent them from buying more than 120 tablets within a month.

The response of the pharmaceutical companies was to plunge ahead with the only remaining drug that could be sold freely on shelves. “[Phenylephrine] went from maybe one product to 261,” Hendeles said. “The drug companies wanted to sell it in airports and cruise ships and in convenience stores and so they would have lost a lot of sales if they didn't make that switch.” Since then, sales of the ineffective — but much easier to buy — decongestants have dwarfed sales of the effective, but harder-to-buy drugs.

But how did an ineffective drug ever get approved by the FDA? Like dozens of other drugs on pharmacy shelves, phenylephrine-based decongestants were grandfathered in from the days when the agency required evidence of safety but not efficacy. It wasn’t until 1962 that an act was passed requiring drugs to be tested for efficacy.

At the time, the FDA attempted to sort through the hundreds of drugs already on the shelves by grouping products into categories and using expert panels to give their blessing to those categories. Phenylephrine got lumped in with the effective decongestants.

When Hendeles and a UFL colleague, Randy Hatton, examined the studies used by the FDA to make that call, they found that some of the studies were flawed. Moreover, Hatton told me, some of the better studies were damning. In randomized controlled trials, some volunteers were exposed to allergens for hours. They reported relief from the old Sudafed, while the phenylephrine drugs offered no more decongestant effect than a placebo.

Some over-the-counter drugs may provide a small benefit even if they don’t clear the sinuses. For instance, some allergy medications contain an antihistamine in addition to phenylephrine so they can relieve watery or itchy eyes, and some cold and flu medications also have acetaminophen (Tylenol) and this can make people feel better by reducing pain and fever.

But there are downsides to overselling what a drug can provide. People may be tempted to take more that what’s recommended to get the hoped-for decongestant effect. And even a small overdose of acetaminophen can cause permanent liver damage. According to some recent statistics, acetaminophen is America’s leading cause for calls to Poison Control and is responsible for 56,000 emergency department visits per year. It is the No. 1 reason for acute liver failure.

In a news story in the New York Times, an industry spokesperson suggested that taking away over-the-counter phenylephrine drugs would add an increased burden on the “already-strained US health care system.” But people are not burdening the health care system by asking pharmacists for help picking the right over-the-counter drug, even if it’s one stored behind the counter. That’s what pharmacists are trained to do.

Taking ineffective medicines off the shelves might actually reduce the strain on the health-care system by restoring some public faith in it. Low public trust in the system is one reason people forego effective drugs and vaccines — and end up getting sicker.

Congress lately seems concerned with undercutting the FDA, but the opposite is needed: Lawmakers should give the FDA more resources and more power to separate useful drugs from useless ones. And unproven supplements and homeopathic remedies should be moved to a separate section of the store. Pharmacies should be consumer-friendly places, where people never have to worry about being conned.

This column does not necessarily reflect the opinion of the editorial board or Bloomberg LP and its owners.

F.D. Flam is a Bloomberg Opinion columnist covering science. She is host of the “Follow the Science” podcast.