Amrix (Cyclobenzaprine) Oral: Uses, Side Effects, Dosages

What Is Amrix?

Amrix (cyclobenzaprine) is a prescription medication used to treat pain and tenderness caused by muscle spasms. 

Amrix belongs to a group of medications called skeletal muscle relaxants. These drugs work on receptors in the brain and nervous system, causing your muscles to relax. 

Because Amrix is available as an extended-release capsule, you'll only have to take your dose once per day.

Drug Facts

Generic Name: Cyclobenzaprine

Brand Name(s): Amrix, Fexmid, Flexeril, FusePaq Tabradol

Administration Route(s): Oral

Drug Availability: Prescription

Therapeutic Classification: Skeletal muscle relaxant

Available Generically: Yes

Controlled Substance: N/A

Active Ingredient: Cyclobenzaprine

Dosage Form(s): Tablet, suspension, extended-release capsule

What Is Amrix Used For?

The Food and Drug Administration (FDA) approved Amrix to treat muscle spasms caused by acute musculoskeletal conditions, including low back pain and neck pain.

Healthcare providers often prescribe Amrix after other treatments, such as Advil or Motrin (ibuprofen) or Aleve (naproxen), have failed. Amrix improves pain and tenderness, as well as your ability to move the affected area.

You should use Amrix along with rest and physical therapy, and only take it for short periods—up to two to three weeks.

Verywell / Zoe Hansen

How to Take Amrix

Take Amrix once a day at the same time each day. Follow your healthcare provider's instructions for how much to take. Because Amrix comes as an extended-release capsule, be sure to swallow the capsule whole without chewing—this could affect how quickly the medication is released into your body and cause side effects.

Storage

Store your Amrix prescription at room temperature in its original container. Keep all your medications in a safe location, out of the reach of children and pets.

Off-Label Uses

Healthcare providers may prescribe medications for off-label uses, meaning not approved for conditions by the FDA.

Off-label conditions Amrix is used to treat include:

How Long Does Amrix Take to Work?

Amrix begins to work the first day you start taking it, likely within a few hours. Most people experience the full effects of Amrix after two weeks of treatment.

What Are the Side Effects of Amrix?

This is not a complete list of side effects, and others may occur. A medical professional can advise you on side effects. If you experience other effects, contact your pharmacist or a medical professional. You may report side effects to the FDA at www.fda.gov/medwatch or 800-FDA-1088.

As with other medications, Amrix can cause side effects. Talk to your healthcare provider about any side effects you experience.

Common Side Effects

Watch out for these common side effects, and let your healthcare provider know if they don't go away:

Constipation (having trouble passing stool)
Dizziness 
Drowsiness 
Dry mouth
Fatigue 
Nausea 
Upset stomach

If you find that Amrix makes you tired, you may want to take your dose at night.

Severe Side Effects

In rare cases, Amrix may cause serious side effects. Call your healthcare provider right away if you think you are experiencing a serious reaction. Call 911 if your symptoms feel life-threatening or if you think you're having a medical emergency.

Serotonin Syndrome

Rarely, Amrix, when used in combination with certain other drugs, can cause serotonin syndrome. Serotonin syndrome involves a buildup of serotonin (a chemical messenger and key hormone stabilizing mood) in your body and can be life-threatening.

Call your healthcare provider at once if you experience any of the following symptoms:

Agitation or restlessness 
Big pupils or side-to-side eye movements 
Confusion, hallucinations, or other changes in mental status 
Fast heartbeat or quick breathing 
Muscle stiffness or muscle spasms 
Nausea, vomiting, or diarrhea 
Nervousness, insomnia, or tremor 
Sweating or fever 
Trouble with coordination or balance

Heart Problems

Although uncommon, Amrix can affect your heart and lead to heart attack (when blood flow to the heart is blocked) or stroke (when blood flow to the brain is interrupted or reduced). Seek medical care urgently if you experience:

Fast heartbeat (tachycardia) 
Irregular or abnormal heartbeats (arrhythmias)

Allergic Reaction

Stop taking Amrix and let your healthcare provider know right away if you develop any signs of an allergic reaction, including:

Difficulty breathing 
Hives 
Itching 
Swelling of the face or tongue

Report Side Effects

Amrix may cause other side effects. Call your healthcare provider if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your provider may send a report to the FDA's MedWatch Adverse Event Reporting Program or by phone (800-332-1088).

Dosage: How Much Amrix Should I Take?

The dose of this medicine will be different for different patients. Follow your doctor's orders or the directions on the label. The following information includes only the average doses of this medicine. If your dose is different, do not change it unless your doctor tells you to do so.

The amount of medicine that you take depends on the strength of the medicine. Also, the number of doses you take each day, the time allowed between doses, and the length of time you take the medicine depend on the medical problem for which you are using the medicine.

For relaxing stiff muscles:
- For oral dosage form (extended-release capsules):
  - Adults—15 milligrams (mg) once a day. Some patients may need 30 mg (one 30 mg capsule or two 15 mg capsules) per day.
  - Children—Use and dose must be determined by your doctor .
- For oral dosage form (tablets):
  - Adults and children 15 years of age and older—10 milligrams (mg) 3 times a day. The largest amount should be no more than 60 mg (six 10-mg tablets) a day.
  - Children younger than 15 years of age—Use and dose must be determined by your doctor.

 Modifications

If you have difficulty swallowing pills, you're not alone. Many adults have trouble with this, especially if the capsule is large. Fortunately, Amrix may be opened and sprinkled onto applesauce.

Follow these steps for safely taking your dose:

Fill a tablespoon with applesauce and set the spoon down on a clean paper towel. 
Hold your Amrix capsule in the upright position over the tablespoon.
Gently twist both ends of the capsule in opposite directions until the capsule opens. 
Carefully sprinkle the granules inside the capsule onto the applesauce. Check to make sure the capsule is empty, and then throw the capsule away. 
Swallow the applesauce immediately, being careful not to chew. Do not save the applesauce for later use.
Rinse with a sip of water and swallow to make sure no Amrix granules remain stuck in your mouth.

Missed Dose

If you forget to take your dose of Amrix, take it as soon as you remember. If it's almost time for your next dose, skip the missed dose. Do not double up or take extra. Taking more than your prescribed dose can cause side effects.

Overdose: What Happens If I Take Too Much Amrix?

Taking more than your recommended dose of Amrix can be dangerous. Overdosing on Amrix can cause serious symptoms, including death. If you or someone else has overdosed on Amrix, it is important to seek medical care immediately since symptoms can progress quickly.

Overdose symptoms include:

Abnormal heart rhythm 
Agitation
Changes in blood pressure (up or down) 
Chest pain 
Coma 
Confusion 
Dizziness 
Drowsiness 
Fast heartbeat
Fever
Hallucinations 
Muscle stiffness
Nausea and vomiting 
Problems with coordination or balance
Seizures 
Slurred speech
Sweating 
Tremors

What Happens If I Overdose on Amrix?

If you think you or someone else may have overdosed on Amrix, call a healthcare provider or the Poison Control Center (800-222-1222).

If someone collapses or isn't breathing after taking Amrix, call 911 immediately.

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.

What Are Reasons I Shouldn't Take Amrix?

Certain conditions increase your risk of developing complications from Amrix. Your healthcare provider will likely recommend a different treatment if any of the following apply to you:

You have or had recent heart problems, including a recent heart attack, heart rhythm problems (arrhythmias), heart block (slowing down of electrical signals in the heart), heart conduction problems, or heart failure.
You have hyperthyroidism (an overactive thyroid).
You take a monoamine oxidase inhibitor (MAOI) or have recently stopped taking an MAOI within the last 14 days. These medications are often used for depression and include Marplan (isocarboxazid), Nardil (phenelzine), Eldepryl or Zelapar (selegiline), and Parnate (tranylcypromine). 
You have had a previous allergic reaction to Amrix or any component of the product.

What Other Medications Interact With Amrix?

Many drugs may interact with Amrix, including over-the-counter (OTC) nonprescription products. Keep an updated list of all the medicines you take. Share this information with your healthcare providers and pharmacist any time there are changes.

Some common drug interactions to watch for include:

Medications That Increase the Risk of Serotonin Syndrome:

Most antidepressants, including selective serotonin reuptake inhibitors (SSRIs), serotonin-norepinephrine reuptake inhibitors (SNRIs), tricyclic antidepressants, and MAOIs
Cough and cold products containing dextromethorphan or chlorpheniramine 
Drugs of abuse, including ecstasy (also known as MDMA), amphetamine, and cocaine 
Pain medications like fentanyl, tramadol, Demerol (meperidine), and methadone 
Saint-John's-wort 
Zyvox (linezolid)—an antibiotic

Medications That Increase Sedation (Drowsiness):

Alcohol 
Barbiturates, such as phenobarbital 
Benzodiazepines like Xanax (alprazolam) or Klonopin (clonazepam) 
Opioid pain medications such as oxycodone or hydrocodone products
Sleep medicines like Ambien (zolpidem) or Lunesta (eszopiclone)

Medications That Increase Anticholinergic Side Effects (Dry Mouth, Difficulty Urinating, Blurred Vision, Constipation, and Confusion):

Allergy medications 
Antidepressants and antipsychotic medications 
Certain medications for chronic obstructive pulmonary disease (COPD, chronic inflammatory lung diseases causing obstructed air flow in the lungs) and asthma (condition causing narrowing of the airways) 
Drugs used to treat overactive bladder (frequent, sudden urges to urinate)
Medicines used for irritable bowel syndrome (IBS, inflammation of the large intestine) 
Parkinson's disease (progressive nervous system disease affecting movement) drugs

This is not a complete list of all the medications that may interact with Amrix. Always talk to your healthcare provider or pharmacist before starting anything new.

What Medications Are Similar?

Several other skeletal muscle relaxants are available and work similarly to Amrix. Studies comparing the effectiveness of one muscle relaxant to another are lacking. Amrix only needs to be taken once daily to provide 24-hour relief, unlike other skeletal muscle relaxants.

Other skeletal muscle relaxants include:

Lorzone (chlorzoxazone)
Norflex (orphenadrine)
Robaxin (methocarbamol)
Skelaxin (metaxalone)
Soma (carisoprodol) 
Zanaflex (tizanidine)

This is a list of drugs also prescribed to treat muscle spasms. It is not a list of drugs recommended to take with Amrix. In fact, you should not take these drugs together. Ask your pharmacist or doctor if you have any questions about your medications.

Frequently Asked Questions

Amrix is used for the short-term treatment of pain associated with musculoskeletal conditions, including back and neck pain. Amrix is often used after NSAIDs (nonsteroidal anti-inflammatory drugs) like ibuprofen or naproxen have failed. Amrix therapy should be combined with rest and physical therapy.
Amrix works by targeting receptors in the brain and nervous system, causing your muscles to relax. Amrix helps improve pain, tenderness, and your ability to move the affected area.
Never take MAOIs with Amrix. These include certain antidepressants and medications used to treat Parkinson's disease. Do not start Amrix within 14 days of stopping an MAOI. Many other drugs may interact with Amrix. Always talk to your healthcare provider or pharmacist before starting anything new.
The most common side effects of Amrix include constipation, dizziness, drowsiness, dry mouth, fatigue, nausea, and upset stomach. Let your healthcare provider know if any of these symptoms persist or affect your ability to take Amrix.
Let your healthcare provider know if the following conditions apply to you since they can affect your ability to take Amrix safely:
- You have hyperthyroidism.
- You take an MAOI medication or stopped taking an MAOI in the last 14 days.
- You've had a reaction to Amrix in the past.
- Recent heart attack or other heart problems.
Amrix is generally not recommended for older individuals since they are more likely to develop side effects.

How Can I Stay Healthy While Taking Amrix?

If you're struggling with muscle pain that won't go away, Amrix may be able to help—primarily if other treatments like Advil or Motrin or Aleve haven't worked. It's important to only take Amrix for the amount of time your healthcare provider has prescribed. The effectiveness and safety of using Amrix long term are unknown.

If your symptoms persist after a few weeks, talk with your provider. Together, you will come up with a plan to get you feeling better and back to doing the things you enjoy.

Medical Disclaimer

Verywell Health's drug information is meant for educational purposes only and not intended as a replacement for medical advice, diagnosis, or treatment from a healthcare professional. Consult your doctor before taking any new medication(s). IBM Watson Micromedex provides some of the drug content, as indicated on the page.

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