Do they work? Yes. Over-the-counter decongestants relieve stuffy sinuses by shrinking the blood vessels that stop up the nose. Choose a product that contains pseudoephedrine (like Sudafed). You'll have to ask for it at the pharmacy counter—in 2005, the FDA put limits on how much an individual can purchase because pseudoephedrine is commonly used to make methamphetamine. That said, the drug is safe for most people and among the most effective cold remedies available.
"The quick rule of thumb is if you can buy it without showing an ID, don't bother. It's not going to work," says Ally Dering-Anderson, clinical assistant professor of pharmacy practice at the University of Nebraska Medical Center. Those with high blood pressure should stick to spray-based decongestants such as Afrin 12 Hour. This won't stray into your bloodstream, says Alonzo.
Source : http://abcnews.go.com/Health/Wellness/truth-10-counter-cold-remedies/story?id=22378376