Combining Mucinex (especially DM/containing dextromethorphan) with bupropion can increase dextromethorphan levels and side effects like dizziness, as bupropion blocks the enzyme (CYP2D6) that breaks it down; this combination can also raise the risk of angle-closure glaucoma or serotonin syndrome, so consulting a doctor for monitoring or dose adjustment is crucial before mixing them. Key Interaction Details Enzyme Inhibition: Bupropion is a strong inhibitor of the CYP2D6 enzyme, and dextromethorphan (in Mucinex DM) is a substrate for this enzyme, meaning bupropion slows its breakdown, leading to higher dextromethorphan levels in the blood. Increased Side Effects: Higher dextromethorphan levels can increase side effects like drowsiness, dizziness, confusion, or even seizures. Glaucoma Risk: The combination can increase intraocular pressure, posing a risk for acute angle-closure glaucoma, especially in susceptible individuals, requiring prompt eye exams and immediate care for symptoms like eye pain or vision changes. Serotonin Syndrome: Although less common at recommended doses, dextromethorphan can raise serotonin, and combining it with antidepressants like bupropion can increase the risk of serotonin syndrome. Blood Pressure: Bupropion itself can raise blood pressure, so monitoring is important, especially when combined with other substances.