Dextromethorphan, or DXM, is a common ingredient found in numerous over-the-counter cough and cold suppressants. While used therapeutically for cough relief, ingesting high doses alters consciousness, leading to confusion about its classification. The question is whether DXM functions as a psychedelic, like LSD, or as a dissociative, such as ketamine. Understanding the chemical action and subjective effects of DXM resolves this classification.
Defining Classic Psychedelics and DXM
The term “classic psychedelic” refers to psychoactive compounds, such as psilocybin and lysergic acid diethylamide (LSD). These compounds are defined by their primary action as agonists on the 5-HT2A serotonin receptor in the brain. Activation of this receptor causes the profound alterations in perception, emotion, and cognition that characterize a traditional psychedelic experience.
Dextromethorphan does not fit this definition, despite its ability to induce hallucinations at high recreational doses. When misused, DXM is classified as a dissociative anesthetic, placing it in the same category as phencyclidine (PCP) and ketamine.
The Distinct Mechanism of Action
The primary psychoactive effects of high-dose DXM are mediated by its action as a non-competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor. These receptors are part of the glutamatergic system, which is the brain’s main excitatory pathway, involved in learning and memory. By blocking the NMDA receptor, DXM disrupts normal signaling, leading to the characteristic sensory and cognitive detachment known as dissociation.
The active metabolite of DXM, called dextrorphan, is actually a more potent NMDA receptor antagonist than DXM itself, mediating much of the drug’s dissociative effects. This mechanism is the scientific basis for its dissociative anesthetic classification, as it mirrors the action of other well-known dissociatives. Classic psychedelics, in contrast, do not significantly interact with the NMDA receptor.
Characteristics of the DXM Experience
The high-dose DXM experience is described as a progression through distinct phases known as “plateaus,” which are directly related to the amount consumed. The first and second plateaus involve mild stimulation, altered perceptions, and euphoria. At higher doses, the experience shifts dramatically.
The third and fourth plateaus introduce significant impairment, profound altered consciousness, and intense out-of-body sensations, derealization, and depersonalization. This overwhelming sense of disembodiment is the defining feature of a dissociative experience, contrasting sharply with the “trip” associated with classic psychedelics.
Safety Concerns and Toxicity
The widespread availability of DXM masks significant dangers associated with its recreational misuse, particularly the risk of Serotonin Syndrome. DXM’s action as a serotonin reuptake inhibitor means it increases serotonin levels in the brain. Taking high doses, especially when combined with other serotonergic medications like Selective Serotonin Reuptake Inhibitors (SSRIs) or Monoamine Oxidase Inhibitors (MAOIs), can lead to a dangerous excess of serotonin.
Serotonin Syndrome is a potentially life-threatening condition characterized by mental status changes, neuromuscular hyperactivity, and autonomic instability. The most common source of misused DXM is combination cold medications, which contain other active ingredients that compound the danger, such as acetaminophen, which can cause severe liver failure in overdose, or antihistamines and decongestants, which can lead to dangerous cardiac effects.