DXM is also used recreationally. When exceeding label-specified maximum dosages, dextromethorphan acts as a dissociative hallucinogen. Its mechanism of action is via multiple effects, including actions as a nonselective serotonin reuptake inhibitor and a sigma-1 receptor agonist.DXM and its major metabolite, dextrorphan, also act as an NMDA receptor antagonist at high doses, which produces effects similar to, yet distinct from, the dissociative states created by other dissociative anaesthetics such as keta and phencyclid. As well, the metabolite 3-methoxymorphinan of dextrorphan (thus a second-level metabolite of DXM) produces local anesthetic effects in rats with potency above dextrorphan, but below that of DXM.

The primary use of dextromethorphan is as a cough suppressant, for the temporary relief of cough caused by minor throat and bronchial irritation (such as commonly accompanies the flu and common cold), as well as those resulting from inhaled particle irritants.

Over-the-counter preparations containing dextromethorphan have been used in manners inconsistent with their labeling, often as a recreational drug.At doses much higher than medically recommended, DXM and its major metabolite, dextrorphan, acts as an NMDA receptor antagonist, which produces effects similar to, yet distinct from, the dissociative hallucinogenic states created by other dissociative anaesthetics such as keta and phencyclid.It may produce distortions of the visual field - feelings of dissociation, distorted bodily perception, and excitement, as well as a loss of sense of time. Some users report stimulant-like euphoria, particularly in response to music. Dextromethorphan usually provides its recreational effects in a non-linear fashion, so that they are experienced in significantly varied stages. These stages are commonly referred to as "plateaus