DXM is dextromethorphan, one of the most widely used cough suppressants in the world. You’ll find it in dozens of over-the-counter cold and cough products, where it works by acting on the brain rather than the throat or lungs. But DXM has a more complex pharmacological profile than most people realize, and in recent years it has gained FDA-approved uses well beyond cough relief, including treatments for depression and uncontrollable emotional episodes.
How DXM Suppresses Cough
Despite being structurally related to opioid compounds, dextromethorphan doesn’t work through the same pathways that drugs like codeine use. Instead, it suppresses the cough reflex primarily by blocking a receptor in the brain called the NMDA receptor, which is involved in nerve signaling, and by activating another target called the sigma-1 receptor, a protein that helps regulate how excitable neurons are. This combination quiets the brain’s cough center without producing the pain relief, euphoria, or significant respiratory depression associated with traditional opioids.
The standard adult dose for cough is 20 mg, taken every 6 to 8 hours as needed. For children, doses are weight-based and given in liquid form. The FDA recommends against using DXM in children under 4 years old, and children under 6 should not receive combination products that contain DXM along with other active ingredients.
FDA-Approved Uses Beyond Cough
DXM now has two additional FDA-approved roles, both in combination with a second drug that changes how the body processes it.
The first came in 2010, when the FDA approved a combination of dextromethorphan and quinidine (sold as Nuedexta) for pseudobulbar affect, or PBA. This is a neurological condition where people experience sudden, uncontrollable episodes of crying or laughing that don’t match how they actually feel. It commonly occurs in people with ALS or multiple sclerosis. Quinidine’s role in the combination is purely metabolic: it blocks the liver enzyme that normally breaks DXM down quickly, allowing higher and more sustained levels of dextromethorphan to reach the brain.
The second approval came in 2022, when the FDA cleared a combination of dextromethorphan and bupropion (sold as Auvelity) for major depressive disorder in adults. This was notable because the combination showed rapid antidepressant effects, likely driven by DXM’s ability to block NMDA receptors and activate sigma-1 receptors. Bupropion serves a similar metabolic role to quinidine here: it slows DXM’s breakdown so the drug stays active longer.
Why Your Genetics Affect How DXM Works
Your body breaks down dextromethorphan using a liver enzyme called CYP2D6, converting it into an active metabolite called dextrorphan. But 5 to 10% of people of European descent are genetically “poor metabolizers,” meaning they produce little or no functional CYP2D6. For these individuals, DXM lingers in the body much longer and at higher concentrations than expected.
In studies, poor metabolizers showed significantly greater psychomotor impairment on the same dose compared to normal metabolizers, with tracking task performance dropping from 95% accuracy to 86%. They also reported more sedation and unpleasant feelings. Interestingly, normal metabolizers reported the drug felt more rewarding, likely because their bodies convert more DXM into dextrorphan, which appears to be the metabolite most responsible for the drug’s abuse potential. This genetic variation helps explain why the same dose of cough syrup can feel barely noticeable to one person and strongly sedating to another.
Common Side Effects
At standard cough-suppressing doses, dextromethorphan is generally well tolerated. The side effects that do occur tend to be mild: dizziness, lightheadedness, drowsiness, nausea, vomiting, stomach pain, nervousness, and restlessness. Most of these resolve on their own and don’t require stopping the medication.
Dangerous Interactions With Other Medications
The most serious safety concern with DXM is serotonin syndrome, a potentially life-threatening reaction that happens when too much serotonin accumulates in the brain. This can occur because dextromethorphan inhibits the reuptake of serotonin, and combining it with other drugs that raise serotonin levels creates a compounding effect.
The highest-risk combinations involve MAO inhibitors, which should never be taken with DXM. But common antidepressants like SSRIs (such as escitalopram) also pose a real risk. Both DXM and SSRIs are metabolized by CYP2D6, meaning the SSRI can slow DXM’s breakdown while both drugs simultaneously boost serotonin. Tricyclic antidepressants and certain opioid medications have also been linked to serotonin syndrome when combined with dextromethorphan. If you take any medication that affects serotonin, check with a pharmacist before using an OTC cough product containing DXM.
Misuse and Abuse Risks
At the 20 mg doses found in normal cough medicine use, DXM is safe and non-intoxicating. But at recreational doses ranging from 300 to over 1,500 mg, the drug produces dissociative effects similar to ketamine or PCP. These effects are dose-dependent and are commonly described in four “plateaus.”
- Plateau 1 (100 to 200 mg): restlessness and mild euphoria.
- Plateau 2 (200 to 500 mg): exaggerated sounds and visuals, closed-eye hallucinations, loss of balance.
- Plateau 3 (500 to 1,000 mg): visual and auditory disturbances, altered consciousness, mania, panic, partial dissociation from reality.
- Plateau 4 (over 1,000 mg): full hallucinations, delusions, complete dissociation, severe loss of coordination.
High doses also cause dangerous physical effects. DXM blocks the reuptake of adrenaline-related chemicals at these levels, leading to high blood pressure and heavy sweating. Combined with the serotonin effects, this makes overdose a medical emergency, particularly when other substances are involved.
Because of these misuse risks, many U.S. states have passed laws restricting the sale of DXM-containing products to people 18 and older. Retailers in these states are required to check ID before completing a sale, unless the buyer clearly appears to be at least 25. These restrictions do not apply when DXM is prescribed by a doctor.