How Long Do the Effects of Cyclobenzaprine Last?
Medically reviewed by Femi Aremu, PharmD
Cyclobenzaprine is a generic prescription medication classified as a skeletal muscle relaxant or muscle relaxant. It is used along with other measures like rest and physical therapy to relax the muscles and relieve pain and discomfort due to sprains, strains, and other muscle injuries.
Cyclobenzaprine is often referred to by the brand names Flexeril (which is no longer available in the United States as a brand-name drug) and Amrix.
If your healthcare provider prescribes cyclobenzaprine, you may be feeling a lot of discomfort and wonder how long the effects of this will medication last. The short answer is that a dose of cyclobenzaprine can last up to six or 24 hours, depending on the formulation, although it may take one or two days initially to start working.
This in-depth article will cover the effects of cyclobenzaprine and provide other important information about this medicine.
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What Is Cyclobenzaprine and How Does It Work?
Cyclobenzaprine is approved by the U.S. Food and Drug Administration (FDA) to relieve muscle spasms associated with acute (short-term) painful musculoskeletal conditions (conditions that involve bones, joints, tendons, and muscles). It is used along with other measures like rest and physical therapy.
Cyclobenzaprine is a skeletal muscle relaxant. It works in the brain (not directly on muscles) to help relieve muscle spasms.
Cyclobenzaprine is taken by mouth and is available as:
An oral immediate-release tablet (in generic form only; many healthcare providers still prescribe this medicine as Flexeril, but the pharmacist will dispense generic cyclobenzaprine). This formulation is approved for use in individuals 15 years and older.
An oral extended-release capsule (available by its brand name, Amrix, and in its generic form). This formulation is only approved in adults 18 years and older.
This medication should only be used for a short time, generally up to three weeks. Though cyclobenzaprine can help symptoms associated with musculoskeletal conditions, it is not effective in treating spasms associated with conditions of the nervous system, like cerebral palsy.
Sometimes, healthcare providers prescribe medication for a use that is not approved by the FDA. This is called off-label prescribing. Cyclobenzaprine is sometimes prescribed off-label for fibromyalgia in adults.
Dosing Cyclobenzaprine
Cyclobenzaprine dosing is as follows:
In adults and adolescents 15 years and older, the starting dose of cyclobenzaprine (immediate-release) is 5 milligrams (mg) by mouth, three times daily. If necessary, the healthcare provider may increase the dose to 7.5 or 10 mg by mouth three times daily.
In adults ages 18 to 64, the starting dose of Amrix (extended-release cyclobenzaprine) is 15 mg by mouth once daily. The healthcare provider may increase the dose to 30 mg by mouth daily if necessary.
Amrix is only approved for people aged 18 years and older, while immediate-release cyclobenzaprine is approved for use in people ages 15 years and older.
Treatment with cyclobenzaprine should generally not be extended beyond two or three weeks.
Cyclobenzaprine is generally not used in older adults (65 years of age and older) due to the risk of side effects like hallucinations, confusion, and heart problems, as well as potential drug interactions. If it is prescribed to someone in this age group, a lower dose will be used, and the person will be closely monitored.
For How Long Is Cyclobenzaprine Effective?
Immediate-release cyclobenzaprine starts working quickly (within about one hour) and reaches its maximum effect within about four hours. However, noticing the full benefit of this medicine may take one or two days.
A dose of immediate-release cyclobenzaprine may be effective in four to six hours. Therefore, it can be prescribed to take three times daily (or about once every eight hours).
A dose of extended-release cyclobenzaprine reaches its maximum effect within about seven to eight hours. Because this formulation is designed to release over time, one dose can last up to 24 hours. This formulation is taken once daily or about once every 24 hours.
Cyclobenzaprine Leaving the Body
Cyclobenzaprine is broken down by enzymes in the body and eliminated by the kidneys in the urine. This takes longer in older people and people with impaired liver function.
The half-life of a drug is the time it takes for one-half of a dose of the drug to be eliminated from the body. It takes about five half-lives for a drug to be mostly eliminated from the body if you stop taking it.
The average half-life of immediate-release cyclobenzaprine is 18 hours but can range from 8 to 37 hours.
This means that, on average, when you stop taking cyclobenzaprine, it will be mostly out of the body within 90 (18 x 5) hours but could range from 40 hours (about 1.5 days; 8 hours x 5 half-lives) to 185 hours (almost 8 days; 37 hours x 5 half-lives).
If you take Amrix (extended-release cyclobenzaprine), however, the average half-life is 32 hours (a little more than one day), and it would take about 160 hours (almost 7 days) for it to completely leave the body.
Side Effects
Common side effects of cyclobenzaprine include:
Dry mouth
Dizziness
Drowsiness
Extreme tiredness
Stomach problems like nausea, heartburn, and constipation
Headache
Call your healthcare provider right away if you experience serious side effects. Call 911 if your symptoms feel life-threatening or if you think you have a medical emergency. Serious side effects can include the following:
Anaphylaxis (serious allergic reaction): Get emergency medical help if you have urticaria (hives), difficulty breathing, or swelling of the face, lips, tongue, or throat.
Safely Taking Cyclobenzaprine
Before taking cyclobenzaprine, tell your healthcare provider about all of your medical conditions and all the medications you take, including:
Prescription drugs
Over-the-counter (OTC) medicines
Vitamins
Dietary supplements
Avoid alcohol while taking cyclobenzaprine. Do not drive until you know how cyclobenzaprine affects you.
Serotonin syndrome is a life-threatening condition caused by the buildup of too much serotonin. It can be life-threatening or cause death if not treated. If you take cyclobenzaprine, the risk of serotonin syndrome is higher if you take other medications that increase serotonin levels. This is one reason your healthcare provider must know all the medicines you take.
Some examples of interacting drugs include:
Selective serotonin reuptake inhibitor (SSRI) antidepressants such as Prozac (fluoxetine)
Serotonin-norepinephrine reuptake inhibitor (SNRI) antidepressants such as Effexor (venlafaxine)
Tricyclic antidepressants such as amitriptyline
Opioid pain medications such as Conzip (tramadol)
Others
You should not take cyclobenzaprine if:
You are allergic to cyclobenzaprine or any ingredient in the medication.
You have taken a drug in the monoamine oxidase inhibitor (MAOI) drug class in the past 14 days.
You have hyperthyroidism (overactive thyroid).
You have certain heart or heart rhythm problems or have recently had a heart attack.
You have moderate to severe liver problems.
Also, in some instances, cyclobenzaprine should be taken with caution, such as in individuals:
With urinary problems
With glaucoma
Who take other medications that cause similar side effects like dry mouth and sedation (these are called anticholinergic effects)
Older adults, for whom sedation leads to further risks, such as injury
If you take extended-release cyclobenzaprine, swallow the capsule whole. Do not chew or crush it. You can also sprinkle the contents of the capsule on 1 tablespoon of applesauce and swallow right away without chewing the mixture.
If you think you took too much cyclobenzaprine, call Poison Control at 1-800-222-1222 right away or call 911 and go to the emergency room. Overdose symptoms may include:
Extreme drowsiness
Vomiting
Fast heartbeat
Shaking
Agitation
How Effective Is It?
One review of many studies found cyclobenzaprine to be more effective than placebo (inactive medicine) in managing back pain but noted that the effect was modest and associated with greater side effects. The researchers found that cyclobenzaprine was most effective in the first four days of treatment.
However, whether any muscle relaxant is better than only using nonsteroidal anti-inflammatory drugs (NSAIDs) for treating acute lower back pain has come into question.
A review published in 2022 found no significant improvement in people treated in the emergency room for low back pain with an NSAID and cyclobenzaprine or any of six other skeletal muscle relaxants compared to treatment with an NSAID and a placebo.
Experts note that cyclobenzaprine is the most studied muscle relaxant, and studies have found it effective for musculoskeletal conditions.
Additionally, the side effect of sedation may help people who have trouble sleeping but could be a concern for older adults who may have an increased risk of injury due to sedation.
The findings among various clinical studies show that cyclobenzaprine is most effective in the first few days of taking it.
Cyclobenzaprine and other muscle relaxants lack evidence of effectiveness for longer-term use and are generally recommended for a maximum of two to three weeks.
Because everyone is different, it's best to consult your healthcare provider for more information about cyclobenzaprine. Your provider can weigh the risks and benefits, taking your specific medical history into consideration and determining whether it is appropriate for you.
Managing Muscle Injuries
In terms of treatment for strains or sprains, a severe injury may require surgery or immobilization (such as with a brace) followed by physical therapy. Your healthcare provider will also likely recommend rest, ice, compression, and elevation (RICE), which help pain and swelling and speed healing. Practicing RICE effectively consists of:
Rest: Try to rest the injured area. This may require a brace or other type of support.
Ice: Applying ice right away helps decrease swelling. Experts recommend icing the area for up to 20 minutes three or four times daily.
Compression: A pressure bandage, such as an elastic bandage or a brace, can help with swelling.
Elevation: Keeping the injured area raised or elevated above the level of your heart.
Pain and discomfort from strains or sprains are generally treated with over-the-counter or prescription oral or topically applied nonsteroidal anti-inflammatory drugs (NSAIDs) and/or muscle relaxants. Note that Tylenol (acetaminophen) is not an NSAID and does not help with symptoms of inflammation.
You can help prevent muscle injuries with these practices:
Include cardiovascular exercise, strength training, and flexibility/stretching into your exercise routine. Incorporating these components will help reduce your chance of injury.
Take turns exercising different muscle groups. Do not exercise the same muscle group on back-to-back days.
Cool down after sports or exercise. Do gentle stretching exercises, holding each stretch for up to 20 seconds.
Drink plenty of water.
Wear the correct equipment or gear along with supportive shoes.
Learn the proper techniques for your sport or exercise.
Rest when you are tired.
If you have an injury, make sure you are completely healed before resuming activity.
Summary
Cyclobenzaprine is a muscle relaxant used for short-term (up to three weeks) treatment of sprains, strains, and other muscle injuries. This medication should be taken along with other measures, like rest and physical therapy.
Immediate-release cyclobenzaprine starts to work within an hour and lasts for four to six hours. Because of this, it can be taken up to three times daily. Extended-release cyclobenzaprine works over time, with one dose lasting up to 24 hours. Because of this, it is taken only once per day.
You can consult your healthcare provider for more information about muscle injuries and which treatment is appropriate for you. It carries a risk of sedation, so exercise caution when taking this medication.
Frequently Asked Questions
How should cyclobenzaprine be stored?
Store cyclobenzaprine at room temperature away from direct light, heat, and moisture. Do not store it in the bathroom. As with all medications, keep out of reach and sight of children and pets. Keep the bottle tightly closed when not in use.
Can I take cyclobenzaprine and Tylenol together?
These drugs do not interact and can be taken together. However, although Tylenol can help with pain, it does not help with swelling and inflammation. If you have inflammation, an NSAID may be more helpful than Tylenol. Check with your healthcare provider or pharmacist to see whether you can take an NSAID with any medical conditions you have and medications you take.
When should I use ice versus heat to treat a muscle injury?
Experts recommend using ice for acute injuries like sprains and strains. Especially during the first few days, ice can help with swelling and bruising. Heat can actually make an acute injury worse. Heat is best for chronic pain (pain lasting longer than four weeks or an older injury) or after swelling has decreased.
Read the original article on Verywell Health.
