Antihistamines block the action of histamine, a chemical that causes allergy symptoms. Antihistamines dry out mucus membranes, so they are often used to relieve runny nose and watery eyes. Antihistamines cause drowsiness, and should be used with caution, especially if you take other medications. Expectorants loosen up phlegm and make it easier to cough up. They help clear airways and make breathing easier.
Suppressants help stifle coughs due to minor throat irritation.
Suppressants are recommended only for those with a dry hacking cough which produces little or no phlegm. Some suppressants are available in topical form, like throat lozenges and ointments that are rubbed into the chest and act like a vaporizer. Herbal treatments and vitamin mega-dosing are the newest trend in alternative medicine. The nutritional supplement industry is not well-regulated, which means that many remedies are unproven, and may be unsafe. Before you try a herbal or vitamin remedy, check with your doctor to make sure you're a good candidate for it, and that it will mix well with your other medications.