About dextromethorphana synthetic morphine (((dextrorotatory methyl ether of levorphanol))) sderivative,a synthetic narcotic antitussive.mechanism of action of dextromethorphandextromethorphan hydrobromide is a selective antitussive which raises threshold of cough centre and suppresses the cough reflex by direct action on the cough centre in the medulla. it does not depress mucociliary function of the airway mucosa and is also devoid of constipating and addicting actions. (((its antitussive action is not exerted through opioid receptors)))ssindications for dextromethorphanschronic nonproductive cough.