Cyclobenzaprine

FLEXERIL

Open Cyclobenzaprine in the interactive console ↗

Pronunciation: sye-kloe-BEN-za-preen

Cyclobenzaprine ballicule: receptor binding, kinetics and half-life diagram — Mechanism of action: Cyclobenzaprine ballicule

Cyclobenzaprine FLEXERIL mascot mnemonic cartoon — Visual mnemonic: Cyclobenzaprine mascot
**“Flexible Cycle bending”**

What it isTricyclic-related central muscle relaxant with H1 and muscarinic antagonism; short-term treatment of acute muscle spasm.

Why this onePronounced sedation can make it useful when nighttime spasm dominates, unlike less sedating relaxants.

What limits itAnticholinergic effects, falls and next-day sedation limit it, especially in older adults. Avoid with MAOIs.

Cyclobenzaprine molecular structure (skeletal formula) — Molecular structure: Cyclobenzaprine

FDA-approved for

muscle spasm (1977)

Off-label

fibromyalgia
insomnia

FDA label

Read the full label on DailyMed ↗

FDA dosing	Population	Start	Target	Max
Muscle spasm, adjunct to rest/PT for acute musculoskeletal conditions	Adults	5 mg TID	5 mg TID	10 mg TID

Renal Undefined

Hepatic Use less frequent dosing in hepatic impairment

Instructions

Do not use for periods longer than 2–3 weeks
Use less frequent dosing in the elderly

Available strengths

tab 5, 7.5, 10 mg
ER cap 15, 30 mg
ODT 2.8 mg
SL tab 2.8 mg

Contraindications

MAOIs (concurrently or within 14 days) due to risk of hyperpyretic crises, severe convulsions, and death
Acute recovery phase of myocardial infarction
Arrhythmias, heart block or conduction disturbances, or congestive heart failure
Hyperthyroidism

Adverse reactions

Drowsiness
Dry mouth
Fatigue
Dizziness
Headache

Pregnancy Undefined

Lactation Undefined

Cost

Cyclobenzaprine (FLEXERIL)

What pharmacies pay · NADAC 9/30/26

Strength		#/mo	generic $/mo	CostPlus
5 mg	tab	90 TID	$1.98	offered
7.5 mg	tab	90 TID	$23.66	offered
10 mg	tab	90 TID	$1.54	offered

Generic entry1989

NO BOXED WARNINGS

Principal riskAnticholinergic burden and sedation

Classes and tags

Clinical profile

Therapeutic safety burden1 / 4

Overdose danger1 / 4

Weight-gain liability0 / 4

Sedation liability3 / 4

QT / Torsades0 / 4

Direct muscarinic antagonism2 / 4

Embryofetal risk1 / 4

Legacy pregnancy categoryUnknown / historical label unavailable

Defining liabilityGenerally tolerated at therapeutic doses; clinically important risks are agent-specific and increase with interactions or organ impairment.

Serotonicity

This drug is routinely called serotonergic. By Gillman’s human-effect criteria it does not raise serotonin in the synapse.

Named as a serotonergic muscle relaxant in the opioid labels, but Gillman places it with the drugs unlikely to be dangerous with an MAOI, alongside amitriptyline. The label still contraindicates MAOIs (concurrently or within 14 days).

Gillman’s four human testsA measurable SERT affinity that fails all four is not clinical serotonicity.