Amrix Side Effects

Generic name: cyclobenzaprine

Medically reviewed by Drugs.com. Last updated on Feb 14, 2025.

Note: This document provides detailed information about Amrix Side Effects associated with cyclobenzaprine. Some dosage forms listed on this page may not apply specifically to the brand name Amrix.

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

Precautions

It is very important that your doctor check your progress at regular visits. This will allow your doctor to see if the medicine is working properly and to decide if you should continue to take it.

If your condition does not improve within 2 or 3 weeks, or if it becomes worse, check with your doctor.

Do not use the extended-release capsules if you have used an MAO inhibitor (MAOI) such as Eldepryl®, Marplan®, Nardil®, or Parnate® within 14 days of each other.

Check with your doctor right away if you have anxiety, restlessness, a fast heartbeat, fever, sweating, muscle spasms, twitching, nausea, vomiting, diarrhea, or see or hear things that are not there. These may be symptoms of a serious condition called serotonin syndrome. Your risk may be higher if you also take certain other medicines that affect serotonin levels in your body.

This medicine will add to the effects of alcohol and other CNS depressants (medicines that slow down the nervous system, possibly causing drowsiness). Some examples of CNS depressants are antihistamines or medicine for hay fever, other allergies, or colds, sedatives, tranquilizers, or sleeping medicine, prescription pain medicine or narcotics, medicine for seizures or barbiturates, other muscle relaxants, or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using this medicine.

This medicine may cause some people to have blurred vision or to become drowsy, dizzy, or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are dizzy or are not alert and able to see well.

Cyclobenzaprine may cause dryness of the mouth. For temporary relief, use sugarless candy or gum, melt bits of ice in your mouth, or use a saliva substitute. However, if your mouth continues to feel dry for more than 2 weeks, check with your medical doctor or dentist. Continuing dryness of the mouth may increase the chance of dental disease, including tooth decay, gum disease, and fungus infections.

Common side effects of Amrix

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:

Serious side effects of Amrix

Along with its needed effects, cyclobenzaprine (the active ingredient contained in Amrix) 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:

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

Symptoms of overdose

• convulsions (seizures)
• drowsiness (severe)
• dry, hot, flushed skin
• fast or irregular heartbeat
• hallucinations (seeing, hearing, or feeling things that are not there)
• increase or decrease in body temperature
• troubled breathing
• unexplained muscle stiffness
• unusual nervousness or restlessness (severe)
• vomiting (occurring together with other symptoms of overdose)

For healthcare professionals

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

General adverse events

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

Nervous system

• 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]

Elderly patients may be particularly susceptible to the sedation and confusion which may accompany cyclobenzaprine therapy.^[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]

See also:

Frequently asked questions

• How much cyclobenzaprine can I take?
• How long does it take for Flexeril to work?
• Is cyclobenzaprine a controlled substance or addictive?
• How long does Flexeril stay in your system?
• Can I take cyclobenzaprine and Tylenol together?

Further information

Amrix side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer