CYCLOBENZAPRINE (Flexeril): What is used for?

What is Cyclobenzaprine?

Cyclobenzaprine is a drug used to treat muscle spams. The product ingredient is Cyclobenzaprine hydrochloride (hcl).
The brand names of Cyclobenzaprine in the United States are: Flexeril, Fexmid, Amrix.

Mechanism of Action (MOA)

Muscle relaxant, structurally and pharmacologically related to tricyclic antidepressants.

Relieves muscle spasms through a central effect, mainly in the brainstem while it lacks activity at the level of the neuromuscular junction and has no direct effect on skeletal muscle, nor is it a peripheral muscle blocker.

Therapeutic Indications, Uses and Benefits of Cyclobenzaprine

Relief of muscle spasms associated with acute painful musculoskeletal conditions.

Dosage of Cyclobenzaprine

Oral dose. 10 mg/8 h.

The dose varies between 20-40 mg/day, in fractional doses, max. 60 mg/day.
Do not exceed 3 weeks of treatment.

Mode of administration

Oral use. Administer with a little liquid (water, juice, milk, etc.).


Hypersensitivity to cyclobenzaprine, arrhythmias, cardiac conduction disturbances, CHF, recent myocardial infarction, hyperthyroidism, concomitant with MAOIs or has been taking MAOIs in the last 14 days before starting treatment with this active ingredient.

Warnings and Cautions

Moderate or severe liver failure, high blood pressure, epilepsy, elderly, urinary retention, closed-angle glaucoma, concomitant with other CNS depressants.

Liver failure

Caution in moderate or severe liver failure. With moderate or severe hepatic insufficiency should be used with caution for the possible increase of plasma concentrations.

Interactions with Cyclobenzaprine

  • Hypertensive crises or severe seizures with: antiparkinsonians, MAO B inhibitors (rasagiline, selegiline); antidepressants, MAO A inhibitors (tranylcypromine, moclobemide), analgesics (tramadol), antibacterials (linezolid).
  • Simultaneous use with substances that also prolong the QT interval, such as, is not recommended: antiarrhythmics (dronedarone, amiodarone, disopyramide, flecainide, ranolazine), antianginoses (ivabradine) and beta-blockers (sotalol), antineoplastics (arsenic trioxide), lapatinib, nilotinib, pazopanib, sunitinib, vemurafenib, vinflunine), macrolide antibiotics (clarithromycin, erythromycin, telithromycin), quinolones (levofloxacin), moxifloxacin), antifungals (fluconazole, voriconazole), antipsychotics (pimozide, asenapine, clozapine, droperidol, paliperidone, ziprasidone), antidepressants (fluoxetine), other substances acting in the CNS (methadone, tetrabenazine, pasireotida), sodium phosphate, anti-asthmatics (formoterol), antimalarials (lumefantrine).
  • Increased toxicity with: CNS depressants and anticholinergics.Increased risk of s. serotonergic with: antineoplastics (procarbazine), anti-migraines (amylotryptan), antidepressants (duloxetine, hydroxytryptophan, trazodone, desvenlafaxine, escitalopram).
  • Decreases antihypertensive action of: guanetidine.
  • Increases the depressant effect of: alcohol, other CNS depressants.


Cyclobenzaprine should not be used during pregnancy unless the potential benefit over the potential risk justifies it.


It is not known whether cyclobenzaprine is excreted in breast milk.

Because this active ingredient is similar to tricyclic antidepressants, some of which are excreted in breast milk, caution and vigilance are advised when given to breastfeeding women.

Effects on driving ability

Cyclobenzaprine may cause drowsiness, dizziness, blurred vision in some patients.

Caution is advised in the use of dangerous vehicles or machinery and in the performance of other activities that require a special state of alertness.

Adverse reactions and side effects of Cyclobenzaprine

Drowsiness, dry mouth and dizziness.


Source: The content of this active ingredient has been written taking into account the clinical and molecular information of all medicines authorised and marketed in the United States under the Unique Ingredient Identifier (UNII) by the Substance Registration System (SRS) of the Food and Drug Administration (FDA) and the United States Pharmacopeia (USP).

In order to know in detail the information authorized by the FDA for each drug, you should consult the corresponding medication guide authorized by the FDA.


PubChem CID: 2895
NCI Thesaurus: C28947

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