Advisers to the Food and Drug Administration voted unanimously on Tuesday against the effectiveness of the key drug found in popular versions of Sudafed, Dayquil and other medications stocked on store shelves.

The FDA assembled its outside advisers to take another look at phenylephrine, which became the main drug in over-the-counter decongestants when medicines with an older ingredient — pseudoephedrine — were moved behind pharmacy counters. A 2006 law had forced the move because pseudoephedrine can be illegally processed into methamphetamine.

If the FDA follows through on the panel's recommendations, Johnson & Johnson, Bayer and other drugmakers could be required to pull their oral medications containing phenylephrine from store shelves. That would likely force consumers to switch to the behind-the-counter pseudoephedrine products or to phenylephrine-based nasal sprays and drops.