Dextromethorphan is a medication that suppresses coughs without phlegm caused by infections such as the common cold, according to WebMD. Patients should not use this medication to treat coughs caused by asthma or emphysema. Dextromethorphan works by decreasing the brain signals that cause a person to cough, notes MedlinePlus.
Dextromethorphan provides temporary cough relief, but it does not cure or shorten the time of the infection, states WebMD. The medication is generally taken as needed once every four to 12 hours. Parents should not give the medication to children less than 6 years old, unless told to do so by their physician. Side effects of dextromethorphan include dizziness, drowsiness nausea and vomiting, notes MedlinePlus.