What is dextromethorphan? Dextromethorphan is a cough suppressant. It affects the signals in the brain that trigger cough reflex. Dextromethorphan is used to treat a cough. It is available over-the-counter alone and is also present in many over-the-counter and prescription combination medications. Dextromethorphan will not treat a cough that is caused by smoking, asthma, or emphysema. Warnings
Do not use dextromethorphan if you have used an MAO inhibitor such as isocarboxazid (Marplan), phenelzine (Nardil), rasagiline (Azilect), selegiline (Eldepryl, Emsam), tranylcypromine (Parnate), or methylene blue injection within the past 14 days. Serious, life-threatening side effects can occur if you take dextromethorphan before the MAO inhibitor has cleared from your body.
Ask a doctor or pharmacist about using dextromethorphan if you have emphysema or chronic bronchitis.