dextromethorfan

Dextromethorphan, also known as DM or DXM, is a synthetic antitussive used in many over-the-counter cough medicines. It is the dextrorotatory isomer of a morphinan compound related to codeine but has little to no analgesic activity at normal doses. It is primarily included for its cough-suppressing effects rather than for pain relief.

Dextromethorphan acts centrally on the brainstem cough center. Its antitussive effects are thought to result from multiple mechanisms, including antagonism of NMDA receptors and modulation of sigma-1 receptors. The exact contribution of each target to cough suppression is not fully defined, and the drug does not produce strong opioid effects at usual doses.

DXM is rapidly absorbed and extensively metabolized in the liver by the enzyme CYP2D6 to dextrorphan (DXO), which also has NMDA receptor antagonism and psychoactive properties. The extent of metabolism varies among individuals due to genetic differences in CYP2D6, leading to variability in effects and risk of side effects.

Therapeutic doses are generally well tolerated but can cause dizziness, drowsiness, or stomach upset. At higher, non-prescribed doses, DXM can induce dissociative or hallucinogenic effects, confusion, ataxia, and tachycardia. It can interact with monoamine oxidase inhibitors and with serotonergic drugs (such as SSRIs or SNRIs), increasing the risk of serotonin syndrome.

Dextromethorphan is widely available over the counter in many countries. Some jurisdictions place age or package restrictions to deter abuse, and misuse or chronic high-dose use is a safety concern, especially among adolescents.