Relaxants

Relaxants are drugs that reduce nervous system activity to promote relaxation, relieve muscle tension, or lessen spasms. They include centrally acting agents that depress CNS activity and peripheral agents that reduce muscle contraction. The term is often used in clinical contexts to describe muscle relaxants and certain sedative medications.

Commonly used categories include central nervous system–acting muscle relaxants such as cyclobenzaprine, methocarbamol, orphenadrine, tizanidine, and baclofen; benzodiazepines such as diazepam when used for muscle spasm or anxiety; and peripherally acting agents such as dantrolene and botulinum toxin injections. Some medicines serve both roles, providing anxiolysis and muscle relaxation.

Mechanisms vary: benzodiazepines enhance GABA-A receptor signaling producing sedation and relaxation; baclofen activates GABA-B receptors to reduce spinal reflexes; tizanidine is an alpha-2 adrenergic agonist that lowers muscle tone; dantrolene interferes with calcium release in skeletal muscle; botulinum toxin blocks acetylcholine release at the neuromuscular junction; nonprescription options like ethanol act as CNS depressants but are not recommended for medical use.

Medical uses include relief of acute musculoskeletal pain with spasms, management of chronic spasticity due to neurological disorders, and, for some benzodiazepines, treatment of anxiety or insomnia under medical supervision. Botulinum toxin injections provide targeted relaxation of overactive muscles in focal dystonias or spasticity.

Potential adverse effects include drowsiness, dizziness, cognitive impairment, and impaired coordination. Dependence and withdrawal can occur with benzodiazepines and some sedatives. Interactions with alcohol or other depressants can markedly increase sedation and respiratory depression. Certain muscle relaxants may cause dry mouth, constipation, or liver or kidney effects, especially with prolonged use.

Safety considerations include avoiding use in severe respiratory insufficiency, acute narrow-angle glaucoma, and severe liver disease (for some agents). Elderly patients are at higher risk of falls and confusion. Therapy should be individualized and periodically reassessed to minimize exposure and dependence.