Cough suppressants are medicines that prevent or stop coughing. They act on the center in the brain that controls the cough reflex, and are meant to be used only to relieve dry, hacking coughs associated with colds and flu. They should not be used to treat coughs that bring up mucus or the chronic coughs associated with smoking, asthma, emphysema or other lung problems.

Many cough medicines contain cough suppressants along with other ingredients. Some combinations of ingredients may cancel each other's effects. One example is the combination of cough suppressant with an expectorant -- a medicine that loosens and clears mucus from the airways. The cough suppressant interferes with the ability to cough up the mucus that the expectorant loosens.

Dextromethorphan is an ingredient in many cough medicines, such as Vicks Formula 44, Drixoral Cough Liquid Caps, Sucrets Cough Control, Benylin DM and some Robitussin products. These medicines come in capsule, tablet, lozenge, and liquid forms and are available without a physician's prescription.

Dextromethorphan is not meant to be used for coughs associated with smoking, asthma, emphysema, chronic bronchitis, or other lung conditions. It also should not be used for coughs that produce mucus.

A lingering cough could be a sign of a serious medical condition. Coughs that last more than 7 days or are associated with fever, rash, sore throat, or lasting headache should have medical attention. Call a physician as soon as possible.

People with phenylketonuria (a hereditary inability to metabolize phenylalanine, an amino acid) should be aware that some products with dextromethorphan also contain the artificial sweetener aspartame, which breaks down in the body to phenylalanine.

Anyone who has asthma or liver disease should check with a physician before taking dextromethorphan.

Women who are pregnant or breastfeeding or who plan to become pregnant should check with their physicians before taking dextromethorphan.

The dye tartrazine is an ingredient in some cough suppressant products. This dye causes allergic reactions in some people, especially those who are allergic to aspirin.

Side effects of dextromethorphan are rare, but may include nausea, vomiting, stomach upset, slight drowsiness, and dizziness.

Patients who take monoamine oxidase inhibitors (MAO inhibitors) should be aware that also taking products containing dextromethorphan can cause dizziness, fainting, fever, nausea and possibly coma. Do not take dextromethorphan unless a physician permits the use of the two drugs together.

When dextromethorphan is taken with medicines that cause drowsiness, this effect may be enhanced.