Americans spend $3.5 billion annually on over-the-counter cough remedies, but experts say much of this money is wasted.

Guidelines released by the American College of Chest Physicians earlier this year indicate that many of the "active" ingredients in cough remedies may be ineffective, reports the May issue of the Harvard Health Letter.

There are many nonprescription cough medicines, but most contain the same types of active ingredients in a limited number of strengths and combinations. Here are the four main ones:

• Expectorants work by thinning mucus. Studies of their effectiveness vary, and the ACCP "cough committee" didnt endorse them.

• Suppressants work by dampening the cough reflex. They provide short-term relief for chronic bronchitis symptoms, but arent as effective on coughs caused by colds.

• Decongestants work by constricting blood vessels, which shrinks swollen membranes and allows more air to pass through nasal passages. Decongestants can be effective in the short run, but they can cause side effects, and you can become dependent on decongestants in the form of nose drops.

• Antihistamines help regardless of whether a cold or allergies is responsible for the cough.

So what should you take?

The new guidelines advise forgetting the cough and cold medicine and buying an allergy medicine instead.

Choose one that combines an older antihistamine (like brompheniramine, diphenhydramine, or chlorpheniramine) with a decongestant.

On the other hand, if you think a cold or cough medicine works, it probably wont hurt you to stick with it, even if what youre paying for is a placebo effect rather than a proven remedy, according to the Harvard Health Letter.