[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [Skeletal muscle relaxants and spasmolytics](https://durgical.com/en/pharmacology/classes/skeletal-muscle-relaxants-and-spasmolytics/) › Cyclobenzaprine

# 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.

Updated Nov 1, 2026

## Quick facts

**Group**
[Skeletal muscle relaxants and spasmolytics](https://durgical.com/en/pharmacology/classes/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.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## 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 →](https://durgical.com/en/conditions/mechanical-low-back-pain/)

## Adverse effects

### Common

- Drowsiness and dizziness
- Dry mouth, constipation and blurred vision (anticholinergic)
- Fatigue and headache

### Serious (rare, important)

- Serotonin syndrome when combined with other serotonergic drugs
- Arrhythmias, tachycardia and conduction delay (tricyclic-like)
- Urinary retention and angle-closure glaucoma attacks
- More adverse effects in older adults, whose blood levels are higher

## 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

## Memory aid

«Cyclobenzaprine = a tricyclic in disguise»: same anticholinergic effects, same MAOI ban, same heart cautions.

## 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).

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/cyclobenzaprine/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 4

- [Amitriptyline](https://durgical.com/en/pharmacology/amitriptyline/)
- [Methocarbamol](https://durgical.com/en/pharmacology/methocarbamol/)
- [Tizanidine](https://durgical.com/en/pharmacology/tizanidine/)
- [Tramadol](https://durgical.com/en/pharmacology/tramadol/)

## Related conditions 1

- [Mechanical low back pain](https://durgical.com/en/conditions/mechanical-low-back-pain/)

[← Back to the class: Skeletal muscle relaxants and spasmolytics](https://durgical.com/en/pharmacology/classes/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](https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=84c306bf-f34d-4cd6-ae22-5f6488cb3153) (DailyMed (U.S. National Library of Medicine), 2026); [Cyclobenzaprine: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a682514.html) (MedlinePlus (U.S. National Library of Medicine), 2026).

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Representative model, for educational purposes only.

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