Amrix

Introduction

Written by Patricia Weiser, PharmD
Medically reviewed by Brittany A. Duke, PharmD, RPh
Updated on September 20, 2023

Cyclobenzaprine (sye kloe BEN za preen) is a generic medication prescribed to help relieve muscle spasms in adults and some children. It’s a short-term treatment used along with rest and physical therapy. Cyclobenzaprine belongs to a group of drugs called muscle relaxants.

This article doesn’t provide coupons for all forms of cyclobenzaprine. To find coupons for cyclobenzaprine extended-release* oral capsule, see this article.

* “Extended release” means the drug is slowly released into your body over a long period of time.

Side effects of cyclobenzaprine

Cyclobenzaprine may cause mild or serious side effects. More common mild side effects of cyclobenzaprine and its serious side effects are listed below. This article doesn’t include all possible side effects of the drug. Side effects can vary based on your age, overall health, and any other medications you take.

To learn more about cyclobenzaprine’s side effects, see this article or ask your doctor or pharmacist. You can also refer to the prescribing information for cyclobenzaprine listed in the “Resources” section.

Mild side effects

More common mild side effects reported with cyclobenzaprine are listed below.

This article doesn’t include all possible mild side effects of the drug. To learn more about cyclobenzaprine’s side effects based on the form, refer to the prescribing information for cyclobenzaprine listed in the “Resources” section.

With many drugs, mild side effects may go away within a few days or a couple of weeks. If the side effects are bothersome, tell your doctor or pharmacist. They may be able to suggest ways to manage them.

Mild side effects of cyclobenzaprine oral tablet and cyclobenzaprine extended-release* oral capsule commonly include:

• dry mouth
• dizziness
• fatigue (low energy)
• constipation
• mild allergic reaction†

* “Extended release” means the drug is slowly released into your body over a long period of time.
† For details about this side effect, see the “Interactions and warnings for cyclobenzaprine” section.

Serious side effects

Serious side effects of cyclobenzaprine are listed below.

This article doesn’t include all possible serious side effects of the drug. To learn more about cyclobenzaprine’s side effects based on the form, refer to the prescribing information for cyclobenzaprine listed in the “Resources” section.

With many drugs, serious side effects are possible but not common. If you have serious side effects from this drug, call your doctor right away. If you’re having severe symptoms or a medical emergency, call 911 or a local emergency number.

In general, cyclobenzaprine’s serious side effects include:

• heart problems, such as heart rhythm changes or rapid heart rate
• blood pressure changes
• fainting
• liver problems
• confusion
• risk of serotonin syndrome (life threatening reaction due to high levels of serotonin in the body) if taken with certain other medications or supplements
• severe allergic reaction*

* For details about this side effect, see the “Interactions and warnings for cyclobenzaprine” section.

Interactions and warnings for cyclobenzaprine

Below, you’ll find information about cyclobenzaprine’s possible interactions and warnings.

Interactions of cyclobenzaprine

Certain things may affect how a drug works. These include getting vaccines, consuming alcohol or certain foods, or taking the drug with other medications. This effect is called a drug interaction.

Before you take cyclobenzaprine, ask your doctor to check for possible interactions. Be sure to tell them about any of the following you take or use:

• prescription or over-the-counter drugs
• vitamins, herbs, or supplements

To learn about drug-condition interactions, see the “Warnings for cyclobenzaprine” section below.

Warnings for cyclobenzaprine

Some people should not take cyclobenzaprine, and others should take it cautiously.

Cyclobenzaprine could cause harm to people with certain health conditions. This effect is called a drug-condition interaction. Other factors can also affect whether cyclobenzaprine is a safe option for you. These warnings may differ based on the form of cyclobenzaprine you take.

Ask your doctor about specific warnings for cyclobenzaprine, and be sure to tell your doctor about your:

• current health, including any allergies to medications
• past health conditions or surgeries

Allergic reaction

Cyclobenzaprine can cause an allergic reaction in some people. Severe allergic reactions are rare but possible.

If you’ve had an allergic reaction to cyclobenzaprine or any of its ingredients, your doctor will likely not prescribe cyclobenzaprine. They can tell you about medications that are safer options for you.

A mild allergic reaction may cause the following symptoms:

• skin rash
• itchiness
• flushing (temporary warmth, redness, or deepening of skin color)

A severe allergic reaction may cause the following symptoms:

• swelling under your skin, usually in your hands, feet, eyelids, or lips
• swelling of your mouth, throat, or tongue, which can cause breathing problems

If you have an allergic reaction to cyclobenzaprine, call your doctor right away. If you have severe symptoms, call 911 or a local emergency number.

Overdose of cyclobenzaprine

You should not take more cyclobenzaprine than your doctor prescribes. For some drugs, doing so may lead to harmful effects or overdose.

If you think you’ve taken too much cyclobenzaprine, call your doctor or pharmacist right away. Or you could call 800-222-1222 to speak with someone at America’s Poison Centers. You can also use its online resource. If you have concerning symptoms, call 911 or a local emergency number immediately. You can also go to the closest emergency room.

Pregnancy or breastfeeding and cyclobenzaprine

Information about cyclobenzaprine and pregnancy and breastfeeding is described below.

Cyclobenzaprine and pregnancy

It’s not known whether cyclobenzaprine should be taken during pregnancy. If you’re planning a pregnancy or can become pregnant, talk with your doctor before taking this medication.

Cyclobenzaprine and breastfeeding

It’s not known whether cyclobenzaprine should be taken while breastfeeding. If you’re currently breastfeeding or planning to do so, talk with your doctor before taking this medication.

Common questions about cyclobenzaprine

Below you’ll find answers to a few commonly asked questions about cyclobenzaprine.

What brand names are available for cyclobenzaprine?

Cyclobenzaprine is a generic medication. A generic medication is an identical copy of the active drug in a brand-name medication. (An active drug is the ingredient that makes a medication work.) Generic drugs are believed to be as effective and safe as brand-name drugs. And generic drugs typically cost less compared to brand-name drugs.

Currently, Amrix is the brand-name version of cyclobenzaprine extended-release* capsule. Flexeril was the brand-name version of cyclobenzaprine oral tablet in the past. However, Flexeril is no longer available.

If you’d like to know more about Amrix, talk with your doctor or pharmacist.

* “Extended release” means the drug is slowly released into your body over a long period of time.

How does cyclobenzaprine work? And how long does it take to start working?

Cyclobenzaprine works by blocking signals between the central nervous system (CNS) and muscles that result in muscle spasms. It does this by working in the brain and, to a lesser extent, the spinal cord. By acting on the parts of the CNS that control muscles, cyclobenzaprine helps to relax tightened or tense muscles. It’s meant to be used for short-term relief, along with rest and physical therapy.

The timing and duration of cyclobenzaprine’s effects depend on which form of the drug you take. Cyclobenzaprine oral tablet starts working to relax muscles shortly after you take a dose. Its muscle-relaxing effects usually last up to 8 hours.

Cyclobenzaprine oral capsules are extended release (this means the drug is slowly released into your body over a period of time). It takes about 7–8 hours to reach its full muscle-relaxing effects after you take a dose. But these effects usually last for 24 hours.

If you’d like to know more about this, talk with your doctor or pharmacist.

Is withdrawal possible with cyclobenzaprine?

If you suddenly stop taking cyclobenzaprine after you’ve been taking it for a long time, it’s possible to experience withdrawal symptoms. But this isn’t likely because cyclobenzaprine is usually prescribed for short-term use.

Withdrawal symptoms are uncomfortable side effects that can occur when you stop taking a drug your body is used to. After long-term use of cyclobenzaprine, stopping it may rarely cause nausea, headache, or generally not feeling well.

Talk with your doctor to find out how long you should continue taking cyclobenzaprine. They can also give you advice on how to manage any side effects while taking the drug or after stopping it.

Uses of cyclobenzaprine

The Food and Drug Administration (FDA) approves prescription drugs such as cyclobenzaprine for certain conditions. Approved uses for cyclobenzaprine are described below.

Use for muscle spasms

Doctors may prescribe cyclobenzaprine to help relieve muscle spasms. It’s usually prescribed as a short-term treatment. For this purpose, the oral tablet form of cyclobenzaprine is used in people ages 15 years and older. And the oral capsule form is used in adults (people ages 18 years and older).

After an injury, pain signals between the nervous system and muscles may result in spasms (unwanted muscle tension or tightening). Symptoms of muscle spasms include pain and stiffness in the affected muscles. These symptoms may make it difficult to move, work, or even find a comfortable sleeping position.

Cyclobenzaprine is usually prescribed together with physical therapy and rest for short-term muscle spasms.

Cyclobenzaprine only works short term to relieve muscle spasms, for up to 2–3 weeks. Doctors will not prescribe cyclobenzaprine for muscle spasms caused by a nervous system disorder, such as cerebral palsy.

What to ask your doctor

Let your doctor know if you have questions about cyclobenzaprine or would like more details about it.

Here’s a list of some possible questions you may want to ask your doctor:

• Do any of my medications or supplements interact with cyclobenzaprine?
• How often can I take cyclobenzaprine as needed for muscle spasms?
• How long should I wait to drive after taking a dose of cyclobenzaprine extended-release capsule?

Resources

• Cyclobenzaprine hydrochloride extended-release capsules, for oral use. (2020). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/2169667d-4f4b-472d-929b-8a0bcbddbe9c/spl-doc
• Cyclobenzaprine hydrochloride tablets, USP. (2023). https://nctr-crs.fda.gov/fdalabel/services/spl/set-ids/84c306bf-f34d-4cd6-ae22-5f6488cb3153/spl-doc
• Food and Drug Administration. (2023). Orange Book: Approved drug products with therapeutic equivalence evaluations. https://www.accessdata.fda.gov/scripts/cder/ob/index.cfm

Disclaimer: Optum Perks has made every effort to make certain that all information is factually correct, comprehensive, and up to date. However, this article should not be used as a substitute for the knowledge and expertise of a licensed healthcare professional. You should always consult your doctor or another healthcare professional before taking any medication. The drug information contained herein is subject to change and is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. The absence of warnings or other information for a given drug does not indicate that the drug or drug combination is safe, effective, or appropriate for all patients or all specific uses.