Cyclobenzaprine
Skeletal muscle relaxants and spasmolytics
Skeletal muscle relaxants and spasmolytics
A centrally acting muscle relaxant related to tricyclic antidepressants, used for a short time for painful muscle spasm after an acute injury.
Quick facts
- Group
- Skeletal muscle relaxants and spasmolytics
- Target
- Brainstem serotonin and noradrenaline pathways (5-HT2 receptors; exact target uncertain)
- Used for
- Short-term relief of muscle spasm
- Key effects
- Drowsiness and dizziness · Dry mouth
- Monitor
- Duration of use · Sedation
- ATC
- M03BX08
No doses: the clinician sets them by the current guideline.
Mechanism of action
Cyclobenzaprine does not act on muscle or the neuromuscular junction. It works in the central nervous system, mainly the brainstem, reducing tonic somatic motor activity; activity at 5-HT2 receptors is a proposed mechanism. Being structurally a tricyclic, it also has strong anticholinergic, sedative and noradrenaline-potentiating effects, which explain most adverse effects and interactions.
- Acts in the brainstem, not on the muscle
- Tonic somatic motor activity is reduced
- Painful local spasm eases
- Tricyclic effects: sedation and anticholinergic signs
Indications
- Short-term relief of muscle spasm in acute, painful musculoskeletal conditions (e.g., acute low back pain), with rest and physical therapy Mechanical low back pain →
Adverse effects
Common
- Drowsiness and dizziness
- Dry mouth, constipation and blurred vision (anticholinergic)
- Fatigue and headache
Contraindications
- MAO inhibitors now or within the last 14 days
- Acute recovery phase of myocardial infarction; arrhythmias, heart block, conduction disturbances or heart failure
- Hyperthyroidism
- Hypersensitivity
Key interactions
- MAO inhibitors
- Hyperpyretic crisis, seizures and death; contraindicated
- SSRIs, SNRIs, tricyclics, tramadol, bupropion, meperidine, verapamil
- Serotonin syndrome
- Alcohol, barbiturates and other CNS depressants
- More sedation
- Tramadol
- Higher seizure risk
What is monitored
- Duration of use: only for short periods (up to two or three weeks)
- Sedation, confusion and falls, especially in older adults
- Signs of serotonin syndrome with serotonergic co-medication
Pregnancy and breastfeeding
Animal studies showed no harm, but there are no adequate studies in pregnant women; it is used only if clearly needed.
Nursing care
- Ask about MAO inhibitors, antidepressants, tramadol and heart disease before the first dose
- Warn about drowsiness, alcohol and driving
- Check for urinary retention and constipation
- Remind that it complements rest and physiotherapy; it does not treat spasticity of neurological origin
Pharmacokinetics
- Absorption
- Oral; bioavailability about a third to a half
- Metabolism
- Liver (CYP3A4, CYP1A2, some CYP2D6); enterohepatic circulation
- Elimination
- Slow; levels are higher in older adults and in liver impairment
Test yourself
Think of the answer, then tap the question to see it.
Which drug class is cyclobenzaprine structurally related to?
Tricyclic antidepressants (e.g., amitriptyline).
Is cyclobenzaprine useful for spasticity from multiple sclerosis?
No; it is for short-term musculoskeletal spasm, not spasticity of central origin.
Which two contraindications of cyclobenzaprine can you name?
Recent MAO inhibitor use and the recovery phase of myocardial infarction (also arrhythmias, heart failure, hyperthyroidism).
Connections
← Back to the class: Skeletal muscle relaxants and spasmolytics
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - CYCLOBENZAPRINE HYDROCHLORIDE tablet, film coated (DailyMed (U.S. National Library of Medicine), 2026); Cyclobenzaprine: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.