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Cyclobenzaprine (Flexeril): How to Safely Use This Muscle Relaxant

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Feb 23, 2022.

Lower back and neck pain: It's all too common

Chances are that you've pulled your lower back, strained your neck or twisted some other distant muscle in your body at one time or another - most of us have. If you sit at a desk on a daily basis, you may be all too familiar with this pain. Acute muscle injuries often result in a painful, constant spasm and interrupt work, daily activities, and especially sleep.

Luckily, over time, most of these acute injuries heal on their own and life goes on. But how do we survive until the pain subsides?

  • Here, we'll review cyclobenzaprine - Flexeril (brand discontinued), Amrix, and Fexmid - one option that might help you in the short-term.
  • The generic name for Flexeril is cyclobenzaprine, a frequently prescribed skeletal muscle relaxant used for a few weeks or less to help quiet the spasm and ease the pain.
  • However, the brand Flexeril has been discontinued from the US market, so you might most frequently receive this drug by its generic name "cyclobenzaprine" from the pharmacy. It should be very affordable.
  • Using cyclobenzaprine for acute back pain (a "pulled muscle" in your back) is one of its most common uses.

What is cyclobenzaprine used for?

Cyclobenzaprine is a muscle relaxant used in addition to rest and physical therapy for short-term relief of muscle spasm associated with acute, painful musculoskeletal conditions. It is structurally related to the tricyclic antidepressants drug class.

Cyclobenzaprine works by blocking nerve impulses that you recognize as pain and is often combined with over-the-counter (OTC) pain medications like:

Treatment with cyclobenzaprine usually lasts no more than 2 to 3 weeks.

How does cyclobenzaprine come?

There are two different forms of cyclobenzaprine: immediate-release tablets and extended-release capsules. The brand Flexeril is no longer available in the U.S., but your doctor and many consumers may still say "Flexeril" because this common name of cyclobenzaprine is so well-known.

The generic immediate-release cyclobenzaprine tablets come in a 5, 7.5, and 10 milligram (mg) strength. You may find that the 7.5 mg tablet is more expensive, and it may save you money to split the 5 mg tablet in half to achieve a 7.5 mg dose (a 5 mg tablet + 2.5 mg). Ask your doctor and pharmacist about this option.

Most strengths of generic cyclobenzaprine are very affordable, typically costing about $6 to $10 for a bottle of 30 tablets, although some pharmacies may have it for less or you can use a coupon.

Related: Price Guide

The extended-release form of cyclobenzaprine (Amrix) comes as a capsule in a 15 and 30 mg strength. Be sure to check with your insurance if you receive a prescription for Amrix to see if it is covered; many insurance companies have stopped paying for this brand. Also check with the manufacturer for any patient assistance if you are unable to pay. A generic option for Amrix is now available, as well, but may be very expensive, even with a discount coupon.

Typical dosing for cyclobenzaprine

Cyclobenzaprine is used in addition to rest and physical therapy, often with NSAIDs, and treatment duration usually does not exceed 2 to 3 weeks.

Immediate-release tablets: (cyclobenzaprine)

  • Adults and children 15 years of age and older: Initial dose 5 milligrams (mg) orally 3 times a day. If needed, the dose may be increased to 10 mg orally 3 times a day. Start with 5 mg per day in older patients. Use in children under 15 years must be determined by a doctor. Less frequent dosing should be considered in the elderly due to higher blood levels. Use in the elderly not recommended per the Beers Criteria.
  • Liver disease: In mild hepatic impairment the initial dose is 5 mg and is slowly increased. Immediate-release cyclobenzaprine is not recommended in moderate or severe liver disease.

Extended-release capsules: (Amrix)

  • Adults: Initial dose is 15 milligrams (mg) orally once a day; take at the same time each day. If needed, the dose may be increased to 30 mg once a day if needed. Do not crush or chew contents of the capsule. May sprinkle capsule content onto applesauce and consume without chewing; rinse mouth after swallowing applesauce. Use of the extended-release form in children < 18 years has not been approved. Do not use this form in the elderly due to higher blood levels that may cause side effects.
  • Liver disease: The extended-release form of cyclobenzaprine is not recommended for use with any level of liver disease.

Side effects like drowsiness are common

Side effects with cyclobenzaprine can be frequent, bothersome, and sometimes dangerous. Cyclobenzaprine can impair your thinking or how quickly you can react.

Don't drive or do any dangerous activity. Also, avoid combining cyclobenzaprine and alcohol which can worsen these side effects.

  • Drowsiness, fatigue and sedation (up to 40% of patients) is the most common side effect; do not drive or drink alcohol while taking this medication and always check for drug interactions.
  • Dizziness (11%) and confusion (1 to 3%) might increase the risk for a fall, especially in the elderly.
  • Dry mouth (30%) and blurred vision (1 to 3%)
  • Headache (1 to 5%)
  • Constipation (1 to 3%)

Be sure to review the information that comes with your prescription to understand all of the side effects.

How does cyclobenzaprine work?

Acute muscle spasms in the neck or back can be very painful. However, over time the pain should lessen. It is thought cyclobenzaprine, which acts in the brain, boosts levels of norepinephrine and binds to serotonin receptors to reduce spasm and lessen pain.

Muscle relaxants like cyclobenzaprine are usually used with a combination of rest, ice and/or heat, physical therapy, OTC pain relievers -- and time. You might like to join the Muscle Spasm support group to learn about experiences of others.

There's a catch with use of this drug: laying in bed and lack of activity may actually be worse for low back pain or other types of muscle pain and may increase your time to full recovery. Using cyclobenzaprine may make you very drowsy and you may not feel like moving at all. But eventually you should get back to movement.

  • Ask your doctor how you should approach your exercise and movement as you heal from your muscle strain.
  • Two or three sessions of physical therapy, and at-home exercises may speed recovery.
  • Yoga and meditation have been shown to be helpful for some patients, too.
  • You can determine how well your therapy is working based on your relief of muscle spasm and pain, decreasing tenderness, and increased ability to move around more easily.
  • If you don't start to feel relief in a week or two, contact your doctor.

Warnings and precautions

There may be reasons why you shouldn't use cyclobenzaprine at all.

Many skeletal muscle relaxants like cyclobenzaprine can cause "anticholinergic" side effects.

  • Anticholinergic activity blocks the action of the neurotransmitter acetylcholine and can lead to wide range of side effects.
  • Because of this, cyclobenzaprine should be used cautiously if you have certain forms of glaucoma and high blood pressure in the eye, urinary frequency/hesitancy, or if you take other medications that also have anticholinergic effects.
  • If you aren't sure if your medicines have anticholinergic effects, be sure to ask your pharmacist.

You should NOT use cyclobenzaprine during or within 14 days of taking a monoamine oxidase inhibitor (MAOI). MAOIs are used for depression or Parkinson's disease, and include agents such as:

  • isocarboxazid
  • tranylcypromine
  • phenelzine
  • selegeline

Also tell your doctor if you have any thyroid gland or heart problems.

Use in the elderly: Is it safe?

Cyclobenzaprine use in individuals older than 65 should be avoided in most circumstances as there is a higher risk for dangerous side effects.

  • Experts have developed the Beers Criteria, a widely known set of guidelines that lists medications to avoid in the elderly due to the potential for serious side effects.

  • Cyclobenzaprine, a strongly anticholinergic agent, is listed in the Beers Criteria as a potentially inappropriate medication for the elderly 65 years and older.

In general, muscle relaxants like cyclobenzaprine are poorly tolerated in older patients due to anticholinergic effects which can lead to a high risk of:

  • drowsiness, sedation
  • confusion
  • dizziness
  • problems with urination
  • constipation
  • an elevated risk for falls, possibly leading to bone fractures.

Serotonin syndrome and drug interactions

A potentially serious and life-threatening, but uncommon, side effect with cyclobenzaprine is known as serotonin syndrome.

Serotonin syndrome may result in behavioral changes like agitation, confusion, seizures or hallucinations, high blood pressure, excessive sweating, muscle tremors or stiffness, and stomach problems like nausea, vomiting, or diarrhea.

Drug interactions with cyclobenzaprine can boost this risk, too, so always have a pharmacist run a drug interaction screen any time you start or even stop a medication, over-the-counter drug, vitamin, or herbal drug.

Common drugs that could increase this risk include:

Lower back pain treatment

Lower back pain is one of the most common ailments that doctors see in the U.S. However, studies have shown that short-term use of opioid pain killers like hydrocodone or oxycodone is no more effective than using an NSAID like ibuprofen or naproxen alone.

  • Therefore, many doctors are reluctant to prescribe controlled substances like opioids for back pain due to addiction risk and lack of any real added effectiveness over an NSAID.
  • Muscle relaxants have not been shown to add any real benefit over NSAIDs alone.

However, for some patients, short-term use of a muscle relaxant plus an NSAID may help to take the edge off of the pain in the short-run and allow for some much needed sleep. Since drowsiness is a common side effect with muscle relaxants, some doctors may recommend the use of an anti-inflammatory NSAID like ibuprofen or naproxen in the daytime, and add the muscle relaxant just at bedtime.

Flexeril for fibromyalgia

Cyclobenzaprine may be used "off-label" for fibromyalgia, meaning it may be prescribed by your doctor for a generally accepted use not specifically approved by the FDA or listed in package labeling.

For fibromyalgia, cyclobenzaprine has been shown to help with sleep and pain for some patients, but not provide relief for fatigue or tender points.

"Off-label" uses for cyclobenzaprine include:

Your doctor can help guide you to determine if these "off-label" uses are right for you.

List of Muscle Relaxers

In addition to cyclobenzaprine, many other muscle relaxant-type drugs are available:

In the US, diazepam (classified as a benzodiazepine but also used as a muscle relaxant), and carisoprodol are both scheduled as controlled substances and can become habit-forming.

Most skeletal muscle relaxants are available as cost-saving generics in the US.

Finished: Cyclobenzaprine (Flexeril): How to Safely Use This Muscle Relaxant

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  • 2019 Updated AGS Beers Criteria for Potentially Inappropriate Medication Use in Older Adults. American Geriatrics Society Beers Criteria Update Expert Panel. J Am Geriatr Soc 67:674–694, 2019. Accessed Feb. 23, 2022 at
  • Prescription Naproxen as Good as Narcotic Painkillers for Low Back Pain: Study. Accessed Feb. 18, 2020.
  • Flexeril product labeling. McNeil Consumer; Specialty Pharmaceuticals. Accessed Feb. 23, 2022 at
  • Cyclobenzaprine dosage. Accessed Feb. 23, 2022 at

Further information

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