It seems odd that a decongestant taken by millions of Americans likely doesn’t work at all.

Phenylephrine, the main ingredient in popular versions of Sudafed, Allegra, Dayquil and other medications and sold on store shelves, appears to be ineffective when taken by mouth, according to advisers with the U.S. Food and Drug Administration. Nasal sprays and drops containing phenylephrine appear to be more effective, according to FDA reviewers.

Which raises the question: If the products don’t work, why have people kept buying them? The power of suggestion?