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Flexeril Side Effects

Generic name: cyclobenzaprine

Medically reviewed by Drugs.com. Last updated on Feb 14, 2024.

Note: This document contains side effect information about cyclobenzaprine. Some dosage forms listed on this page may not apply to the brand name Flexeril.

Applies to cyclobenzaprine: oral capsule extended release, oral suspension, oral tablet.

Serious side effects of Flexeril

Along with its needed effects, cyclobenzaprine (the active ingredient contained in Flexeril) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking cyclobenzaprine:

Rare

Get emergency help immediately if any of the following symptoms of overdose occur while taking cyclobenzaprine:

Symptoms of overdose

Other side effects of Flexeril

Some side effects of cyclobenzaprine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Less common or rare

For Healthcare Professionals

Applies to cyclobenzaprine: compounding powder, oral capsule extended release, oral tablet, oral and topical kit.

General

The most frequently occurring adverse reactions have included dry mouth, dizziness, fatigue, constipation, nausea, dyspepsia, and somnolence.[Ref]

Nervous system

Elderly patients may be particularly susceptible to the sedation and confusion which may accompany cyclobenzaprine (the active ingredient contained in Flexeril) therapy.[Ref]

Very common (10% or more): Drowsiness (up to 38%)

Common (1% to 10%): Dizziness, somnolence

Postmarketing reports: Headache, serotonin syndrome, seizures, ataxia, tremors, hypertonia, convulsions, abnormal sensations, paresthesia, ageusia[Ref]

Psychiatric

Common (1% to 10%): Irritability, mental acuity decreased, nervousness

Postmarketing reports: Nervousness, confusion, disorientation, insomnia, depressed mood, anxiety, agitation, psychosis, abnormal thinking and dreaming, hallucinations, excitement[Ref]

Hypersensitivity

Postmarketing reports: Anaphylaxis, angioedema, pruritus, facial edema, urticaria, rash[Ref]

Gastrointestinal

Very common (10% or more): Dry mouth (up to 32%)

Common (1% to 10%): Constipation, nausea, dyspepsia, abdominal pain, acid regurgitation, diarrhea

Postmarketing reports: Unpleasant taste, vomiting, anorexia, gastritis, thirst, flatulence, tongue edema[Ref]

Hepatic

Postmarketing reports: Abnormal liver function, hepatitis, jaundice, cholestasis[Ref]

Cardiovascular

Postmarketing reports: Syncope, tachycardia, arrhythmia, vasodilation, palpitation, hypotension[Ref]

Other

Common (1% to 10%): Fatigue

Postmarketing reports: Asthenia, malaise, vertigo[Ref]

Dermatologic

Postmarketing reports: Sweating[Ref]

Genitourinary

Postmarketing reports: Urinary frequency and/or retention[Ref]

Musculoskeletal

Postmarketing reports: Local weakness, dysarthria, muscle twitching[Ref]

Ocular

Postmarketing reports: Blurred vision, diplopia, tinnitus[Ref]

Respiratory

Common (1% to 10%): Upper respiratory infection, pharyngitis[Ref]

Frequently asked questions

References

1. Product Information. Amrix (cyclobenzaprine). A-S Medication Solutions. 2016.

2. Product Information. Flexeril (cyclobenzaprine). Merck & Co., Inc. 2001;PROD.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.