A U.S. Food and Drug Administration (FDA) panel recently confirmed what health care providers and consumers have long suspected: Phenylephrine, a decongestant used in more than 250 over-the-counter cold and flu remedies, doesn't work at all when taken orally. Versions of DayQuil, Sudafed, Tylenol and Theraflu all contain phenylephrine, according to the New York Times.
Though phenylephrine doesn't work in oral medications, it does appear to work when used in nasal sprays, according to CNET. Oral medications containing phenylephrine are still considered safe to use as directed, and may contain other ingredients that can relieve congestion or other cold or flu symptoms.
According to CNN, phenylephrine was originally approved for over-the-counter use in the 1970s, and became more popular in the early 2000s as Congress and state legislatures expanded regulation of pseudoephedrine. A common and effective decongestant, pseudoephedrine was also a key ingredient in the manufacture of the illicit drug methamphetamine. Today, medications that contain pseudoephedrine are only available behind pharmacy counters and require prescriptions in two states.
Medications containing phenylephrine will remain on shelves for now, but for real relief from nasal congestion, consumers should request medications with pseudoephedrine from behind the pharmacy counter. Common side effects can include shakiness or restlessness, according to CNET.