Which adverse effect is commonly seen with CNS-acting muscle relaxants?

• A. Euphoria
• B. Drowsiness
• C. Headache
• D. Nausea

Answer: (B)

Central nervous system–acting muscle relaxants work by dampening neuronal activity in the brain and spinal cord to reduce muscle tone. That CNS depressant effect commonly appears as drowsiness, making somnolence the most characteristic adverse effect. This sedation reflects the same mechanism that relaxes muscles, so patients often feel sleepier, especially when starting treatment or increasing the dose. Because of this, it’s important to avoid driving or operating heavy machinery until you know how the medication affects you, and to steer clear of alcohol or other sedatives that can amplify drowsiness.

Other adverse effects like dizziness or fatigue can occur, and some drugs may cause dry mouth or, in certain cases, low blood pressure. Euphoria and headache or nausea can happen, but they are not the hallmark effects of CNS‑acting muscle relaxants—the prominent, most common one is drowsiness.