Last year, roughly 250 products that contain the decongestant phenylephrine—including popular brands such as Sudafed, NyQuil, Benadryl and Tylenol—rang up sales of nearly $1.8 billion. Just one problem: Oral phenylephrine doesn’t work.

That was the unanimous conclusion of an FDA advisory committee three months ago, based on decades of mounting evidence.

Now, House Republicans want to know why it took the regulator so long to figure it out. Rep. Lisa McClain (Mich.), who chairs the House oversight subcommittee on health care and financial services, has sent (PDF) a letter to FDA commissioner Robert Califf, requesting a briefing on the effectiveness of the over-the-counter (OTC) drugs by Dec. 11.

“We are concerned that phenylephrine has remained approved by the FDA as an OTC drug ‘generally recognized as safe and effective’ (GRASE) for nearly fifty years despite strong scientific evidence supporting the contrary,” McClain wrote.  

In response to a request for comment, the FDA said in an email that it "will review the letter and will respond directly to the Senators/Congressman/Congresswoman."

In September, 16 panelists on the Nonprescription Drugs Advisory Committee (NDAC) agreed to the ineffectiveness of phenylephrine after reviewing data that showed it performed no better—even at high doses—than placebo in relieving congestion.

In 2007, the NDAC came to a similar conclusion on the ineffectiveness of phenylephrine, which first hit the market in 1938. While four subsequent studies showed the ineffectiveness of phenylephrine when taken as a pill, there was enough variability in the results to raise questions about how the studies were conducted.

Phenylephrine is designed to reduce the swelling of blood vessels but the committee recently concluded that when it is taken orally, not enough of the drug reaches the nasal passages. The drug still is effective when delivered by way of a nasal spray or for dilating eyes for use during surgery, the FDA concluded.

The regulator has yet to decide whether to ban the products. In October, CVS Health voluntarily pulled treatments from shelves that contain phenylephrine as their lone active ingredient.