Cyclobenzaprine Stats & Data
Pharmacology
DrugBankDescription
Cyclobenzaprine, a centrally-acting muscle relaxant, was first synthesized in 1961 and has been available for human use since 1977. It was initially studied for use as antidepressant given its structural similarity to tricyclic antidepressants - it differs from Amitriptyline by only a single double bond. Since its approval, it has remained relatively popular as an adjunctive, short-term treatment for acute skeletal muscle spasms secondary to musculoskeletal injury.
Mechanism of Action
The exact mechanism of action of cyclobenzaprine has not been fully elucidated in humans, and much of the information available regarding its mechanism has been ascertained from early animal studies. There is some evidence that cyclobenzaprine exerts its effects at the supraspinal level, specifically within the locus coeruleus of the brainstem, with little-to-no action at neuromuscular junctions or directly on skeletal musculature. Action on the brainstem is thought to result in diminished activity of efferent alpha and gamma motor neurons, likely mediated by inhibition of coeruleus-spinal or reticulospinal pathways, and ultimately depressed spinal cord interneuron activity. More recently it has been suggested that inhibition of descending serotonergic pathways in the spinal cord via action on 5-HT2 receptors may contribute to cyclobenzaprine’s observed effects.
Pharmacodynamics
Cyclobenzaprine is a skeletal muscle relaxant that works on areas of the brainstem to reduce skeletal muscle spasm, though its exact pharmacodynamic behaviour is currently unclear. Despite its long half-life, it is relatively short-acting with a typical duration of action of 4-6 hours. Cyclobenzaprine has been reported to contribute to the development of serotonin syndrome when used in combination with other serotonergic medications. Symptoms of serotonin syndrome may include autonomic instability, changes to mental status, neuromuscular abnormalities, or gastrointestinal symptoms - treatment with cyclobenzaprine should be discontinued immediately if any of these reactions occur during therapy.
Metabolism
Cyclobenzaprine is extensively metabolized in the liver via both oxidative and conjugative pathways. Oxidative metabolism, mainly N-demethylation, is catalyzed primarily by CYP3A4 and CYP1A2 (with CYP2D6 implicated to a lesser extent) and is responsible for the major metabolite desmethylcyclobenzaprine. Cyclobenzaprine also undergoes N-glucuronidation in the liver catalyzed by UGT1A4 and UGT2B10, and has been shown to undergo enterohepatic circulation.
Absorption
The oral bioavailability of cyclobenzaprine has been estimated to be between 0.33 and 0.55. Cmax is between 5-35 ng/mL and is achieved after 4 hours (Tmax). AUC over an 8 hour dosing interval was reported to be approximately 177 ng.hr/mL.
Toxicity
The oral LD50 of cyclobenzaprine in mice and rats is 338 mg/kg and 425 mg/kg, respectively. Signs of overdose may develop rapidly after ingestion and commonly include significant drowsiness and tachycardia, with less common manifestations including tremor, agitation, ataxia, GI upset, and other CNS effects such as confusion and hallucinations. Potentially critical manifestations, though rare, include cardiac arrest or dysrhythmias, severe hypotension, seizures, and neuroleptic malignant syndrome. As the management of cyclobenzaprine overdose is complex and ever-changing, it is recommended that a poison control center be consulted prior to treatment. Typical management involves gastrointestinal decontamination, close cardiac monitoring, and monitoring for signs of CNS or respiratory depression. As cyclobenzaprine exists in relatively low concentrations in plasma, monitoring of drug plasma levels should not guide management and dialysis is likely of no value.
Indication
Cyclobenzaprine is indicated as a short-term (2-3 weeks) adjunct therapy, along with rest and physical therapy, for relief of muscle spasm associated with acute, painful musculoskeletal conditions. It has not been found effective in the treatment of spasticity originating from cerebral or spinal cord disease, or spasticity in children with cerebral palsy. Cyclobenzaprine is also occasionally used off-label for reducing pain and sleep disturbances in patients with fibromyalgia.
Half-life
The effective half-life of cyclobenzaprine in young healthy subjects is approximately 18 hours. These values are extended in the elderly and those with hepatic insufficiency, with a mean effective half-life of 33.4 hours and 46.2 hours in these groups, respectively.
Protein Binding
Cyclobenzaprine is approximately 93% protein bound in plasma. It has been identified as specifically having a high affinity for human serum albumin.
Elimination
After administration of a radio-labeled dose of cyclobenzaprine, 38-51% of radioactivity was excreted in the urine while 14-15% was excreted in the feces. Cyclobenzaprine is highly metabolized, with only approximately 1% of this same radio-labeled dose recovered in the urine as unchanged drug. Metabolites excreted in the urine are likely water-soluble glucuronide conjugates.
Volume of Distribution
The volume of distribution of cyclobenzaprine is approximately 146 L. The combination of high plasma clearance despite a relatively long half-life observed with cyclobenzaprine is suggestive of extensive tissue distribution.
Clearance
The approximate plasma clearance of cyclobenzaprine is 0.7 L/min.
Tolerance & Pharmacokinetics
drugs.wikiTolerance Decay
Tolerance to daytime sedation can develop over several days of repeated use. Given sparse formal data, these values are approximate and based on class inferences and user reports rather than controlled studies.
Cross-Tolerances
Experience Report Analysis
ErowidDemographics
Gender Distribution
Age Distribution
Reports Over Time
Effect Analysis
ErowidEffects aggregated from 61 experience reports (61 Erowid)
Effect Sentiment Distribution
Confidence Distribution
Positive Effects 9
Adverse Effects 4
Dose-Response Correlation
How effect frequency changes across dose levels
View data table
| Effect | Strong (n=11) | Heavy (n=23) |
|---|---|---|
| Sedation | 63.6% | 56.5% |
| Music Enhancement | 45.5% | 21.7% |
| Euphoria | 36.4% | 13.0% |
| Stimulation | 36.4% | 34.8% |
| Anxiety Suppression | 18.2% | 17.4% |
| Tactile Enhancement | 18.2% | 0% |
| Confusion | 0% | 13.0% |
| Auditory Effects | 0% | 13.0% |
| Visual Distortions | 0% | 13.0% |
| Open-Eye Visuals | 0% | 8.7% |
| Nausea | 0% | 8.7% |
| Empathy | 0% | 8.7% |
| Dissociation | 0% | 8.7% |
| Hospital | 0% | 8.7% |
| Headache | 0% | 8.7% |
Dose–Effect Mapping
Experience ReportsHow reported effects shift across dose tiers, based on 61 experience reports.
Limited tier coverage — most reports fall within the Strong / Heavy range. Effects at other dose levels may not be represented.
| Effect | Strong (n=11) | Heavy (n=23) | |
|---|---|---|---|
| sedation | → | ||
| music enhancement | ↓ | ||
| euphoria | ↓ | ||
| stimulation | → | ||
| anxiety suppression | → | ||
| tactile enhancement | — | → | |
| confusion | — | → | |
| auditory effects | — | → | |
| visual distortions | — | → | |
| open-eye visuals | — | → | |
| nausea | — | → | |
| empathy | — | → | |
| dissociation | — | → | |
| hospital | — | → | |
| headache | — | → |
Risk Escalation
Sentiment AnalysisAverage frequency of positive vs adverse effects across dose tiers
View effect breakdown
Adverse Effects
| Effect | Strong (n=11) | Heavy (n=23) | Change |
|---|---|---|---|
| Anxiety Suppression | -4% | ||
| Confusion | — | 0% | |
| Nausea | — | 0% | |
| Headache | — | 0% |
Positive Effects
| Effect | Strong (n=11) | Heavy (n=23) | Change |
|---|---|---|---|
| Music Enhancement | -52% | ||
| Euphoria | -64% | ||
| Stimulation | -4% | ||
| Tactile Enhancement | — | 0% | |
| Empathy | — | 0% |
Dosage Distribution
Dose distribution from experience reports
Real-World Dose Distribution
62K DosesFrom 101 individual dose entries
Oral (n=83)
Insufflated (n=7)
Common Combinations
Most co-occurring substances in experience reports
Form / Preparation
Most common forms and preparations reported
Body-Weight Dosing
Dose relative to body weight from reports with weight data
Redose Patterns
Redosing behavior across 51 reports
Harm Reduction
drugs.wikiCyclobenzaprine has a long effective half-life (about 18 hours IR; ~32 hours ER) and effects can persist into the next day, so plan for next‑day drowsiness and do not drive or operate machinery until fully alert. It is intended for short‑term use (generally ≤ 2–3 weeks) alongside rest and physical therapy; prolonged use lacks strong evidence and increases adverse effects. It is contraindicated in hyperthyroidism, during the acute recovery phase of myocardial infarction, and in patients with arrhythmias, heart block/conduction disturbances, or heart failure. Combining with serotonergic drugs (e.g., SSRIs/SNRIs/MAOIs) has produced case‑reported serotonin syndrome; discontinue and seek care if agitation, hyperreflexia, clonus, or autonomic instability occur. Additive CNS depression occurs with alcohol, opioids, benzodiazepines, and Z‑hypnotics; avoid mixing or use minimal doses with extended spacing if medically unavoidable. Potent anticholinergic properties can cause dry mouth, blurred vision, constipation, urinary retention, confusion, and at high doses anticholinergic delirium; avoid dehydration and hot environments and monitor for urinary retention, especially in males with BPH. Overdose shares tricyclic‑like cardiotoxicity (QRS widening, arrhythmias) and seizure risk; emergent care should include ECG monitoring and serum alkalinization with sodium bicarbonate when QRS is prolonged. Extended‑release capsules must not be chewed or crushed; if swallowing is difficult, contents may be sprinkled on applesauce and swallowed without chewing, then rinse the mouth to avoid retained granules. Hepatic impairment and older age substantially prolong half‑life and raise exposure, warranting lower starting doses (e.g., 5 mg) or avoidance in moderate–severe hepatic disease. Although euphoria is occasionally reported anecdotally at high doses, sedation, dysphoria, and delirium are more common outcomes; deliberate recreational escalation is therefore high‑risk and not recommended.