UNDER STUDY: New guidelines issued by the American College of Chest Physicians provide comprehensive recommendations for the diagnosis and management of cough in adults and kids. According to Richard Irwin, M.D., a pulmonologist at UMASS Medical School in Worcester, Mass., "Cough is the number one reason why patients seek medical attention." Among the doctor's findings includes a surprising discovery: many cough meds don't work to treat coughs caused by colds.

WHAT DOESN'T WORK: The drug guaifenesin -- an expectorant found in products like Robitussin and Mucinex -- doesn't work against coughs caused by colds. Guaifenesin is supposed to work by thinning mucus, allowing people to cough up phlegm. But in four studies done on it, two showed benefit, while two showed no improvement. The expert panel thus concluded there isn't enough evidence to support its use for cough caused by colds. The suppressants codeine and dextromethorphan were also studied. They are supposed to work by quieting the brain's cough center. However, the studies revealed these don't work against coughs caused by colds, although they may be effective against coughs caused by other conditions -- like cancer and bronchitis. Products containing zinc as well as the herb echinacea were also found to have no effect on coughs from colds. The newer antihistamines on the market may also not work. They're the ones touted as "non-drowsy meds;" however, Dr. Irwin says that change may be what makes them ineffective.

WHAT DOES WORK: The older antihistamines -- the ones that do make you drowsy -- were found to be effective in fighting coughs from colds. The ingredient that makes you drowsy actually works by drying up the secretions in the back of your throat. These effective drugs include diphenhydramine -- the active ingredient in Benadryl, dexbrompheniramine -- an active ingredient in Drixoral, and chlorpheniramine -- the active ingredient in Chlortrimeton. Pain relievers called nonsteroidal anti-inflammatory drugs (NSAIDs) may help coughs due to colds -- such as naproxen, the active ingredient in Aleve. Similar drugs, such as ibuprofen in Advil may also then help cough-related colds. However, these drugs may cause stomach upset or increase your risk for gastrointestinal problems.

PLACEBO EFFECT: Dr. Irwin says the reason why one's cough may get better while on one of the medications proven "ineffective" is because of the placebo effect -- shown to be as high as 40 percent in cough studies.

RECOMMENDATIONS: Dr. Irwin says patients with a nagging cough should seek their doctor's advice on how to best treat it. He adds there are medicines out there that will treat just about every kind of cough due to every kind of condition -- so read the label.