Dextromethorphan (DXM) is a cough suppressant found in more than 120 over-the-counter (OTC) cold medications, either alone or in combination with other drugs such as analgesics (e.g., acetaminophen), antihistamines (e.g., chlorpheniramine), decongestants (e.g., pseudoephedrine), and/ or expectorants (e.g., guaifenesin).