Dextrorphan is a substance most notable for its psychoactive effects. It is a metabolite of dextromethorphan, a cough suppressant, or antipertussive, that is a common ingredient in cough syrup and cold medecine. In sufficient amounts, dextrorphan can cause effects such as euphoria, hallucinations and dissociative states.
It is a N-Methyl-D-aspartate (NMDA) receptor antagonist, a class of chemicals that also includes the dissociative drugs phencyclidine (PCP) and ketamine. NMDAs inhibit cellular receptors for the neurotransmitter glutamate. This interferes with normal communication between different areas of the brain, which gives NMDAs their mind-altering characteristics.
Dextrorphan is produced when dextromethorphan enters a person's body and is metabolized by an enzyme called cytochrome. The chemical structure of dextrorphan is similar to dextromethorphan, which is also psychoactive. The mind-altering effects of dextrorphan are much stronger, however, and it is believed that most of the psychoactive effects of taking high doses of dextromethorphan are actually the result of the dextrorphan produced as a result, rather than the dextromethorphan itself. When used medicinally as a cough medicine, a normal therapeutic dose of dextromethorphan — usually less than 50 milligrams — does not normally produce enough dextrorphan to have significant psychoactive effects.
Recreational use usually involves dextromethorphan doses of 100 milligrams or more. This causes feelings of euphoria or excitement, distortions in the user's sense of time and closed-eye hallucinations, a type of visual hallucination that appears only when the user closes his or her eyes or is in a dark area. Higher doses produce a more intense euphoric effect along with hallucinations, a dreamlike mental state and dissociative states that cause the user to feel disconnected from reality or from his or her own body.
The long-term effects of heavy dextrorphan exposure in humans are unclear. Repeated exposure to high doses causes brain lesions in lab rats, but it is not known whether it causes similar effects in humans. Surveys of recreational users, however, indicate that a majority of users report possible side effects such as fatigue, constipation and flashbacks, and a significant minority report impaired memory and attention span, anhedonia and sleep-related problems such as insomnia and frequent nightmares. A small minority also report panic attacks, learning impairment, tremors and physical symptoms such as jaundice and muscle pain. Research is complicated by the fact that many cold medications, which are a common source for recreational users, contain several other chemicals that are harmful if enough cold medicine to induce the psychoactive effects of dextrorphan is taken at once.