Cyclobenzaprine belongs to the family of medications known as muscle relaxants. It is used along with rest and physical therapy for the relief of muscle spasm associated with acute (sudden and short-term) painful conditions. Muscle relaxants work in the central nervous system (CNS) to modify signals from the brain that cause the muscles to tighten. When used in combination with rest and physical therapy, muscle relaxants help to relieve the pain and stiffness caused by muscle spasm.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The usual adult dose of cyclobenzaprine is 10 mg 3 times a day, with a range of 20 mg to 40 mg a day (given in divided doses). The total dose should not exceed 60 mg daily. Use of this medication is not recommended for periods longer than 2 or 3 weeks.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the reach of children.

Do not take this medication if you:

• are allergic to cyclobenzaprine or any ingredients of this medication
• are in the acute recovery phase of heart attack
• are taking MAO inhibitors (such as phenelzine or tranylcypromine) or have taken them in the past 14 days
• have abnormal heart rhythms
• have an overactive thyroid gland (hyperthyroidism)
• have congestive heart failure
• have heart block or conduction disturbances

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• dizziness
• drowsiness
• dry mouth
• fatigue
• indigestion
• nausea

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• constipation
• increased heart rate or fast heartbeat
• symptoms of glaucoma (e.g., blurred vision, seeing halos of bright colours around lights, red eyes, increased pressure in your eyes, eye pain or discomfort)

Stop taking the medication and seek immediate medical attention if any of the following occur:

• symptoms of overdose
• dry, hot, flushed skin
• fast or irregular heartbeat
• hallucinations
• increase or decrease in body temperature
• seizures
• severe decrease in blood pressure
• severe drowsiness
• troubled breathing
• unexplained muscle stiffness
• vomiting occurring together with other symptoms of overdose
• symptoms of serious allergic reaction
• changes in the skin colour of the face
• fast or irregular breathing
• large swellings that look like hives on the face, eyelids, mouth, lips, and/or tongue
• puffiness or swelling of the eyelids or the area around the eyes
• shortness of breath
• skin rash, hives, or itching
• tightness in chest
• trouble breathing
• wheezing
• symptoms of serotonin syndrome
• confusion
• fast heartbeat
• hallucinations
• restlessness
• shaking
• shivering
• sudden jerking of muscles
• sweating

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Drowsiness/reduced alertness: Cyclobenzaprine may impair the ability to perform hazardous tasks such as operating machinery or driving a vehicle. Do not drive or engage in other activities requiring alertness until you determine how the medication affects you.

Glaucoma: This medication may cause increased pressure in the eye, triggering symptoms of glaucoma. If you have glaucoma or elevated pressure in your eye(s), discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Heart rhythm: Cyclobenzaprine can cause changes to the normal rhythm of the heart. If you are at risk for heart rhythm problems (e.g., people with heart failure, angina, low potassium or magnesium levels), discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Length of treatment: The use of cyclobenzaprine for periods longer than 2 or 3 weeks is not recommended.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Serotonin syndrome: Severe reactions are possible when cyclobenzaprine is combined with other medications that act on serotonin, such as certain antidepressants and certain medications for migraine headache. Symptoms of a reaction may include muscle rigidity and spasms, difficulty moving, changes in mental state including delirium and agitation. Coma and death are possible.

If you are taking other medications, discuss with your doctor how these medications may affect your medical condition, how your medical condition may affect the dosing and effectiveness of these medications, and whether any special monitoring is needed.

Urinary problems: Cyclobenzaprine can make urination difficult. People who have difficulty starting urine flow may find that this becomes worse while taking this medication. If you have a history of urinary retention, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Pregnancy: This medication should not be used during pregnancy unless the benefits outweigh the risks. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: This medication may pass into breast milk. If you are breast-feeding and taking cyclobenzaprine, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of cyclobenzaprine for children below the age of 15 have not been established.

Seniors: Due to the increased likelihood of reduced liver function or heart conditions, older adults are at an increased risk of side effects. Doses for seniors are likely to be lower than those for younger adults.

There may be an interaction between cyclobenzaprine and any of the following:

• acetylcholinesterase inhibitors (e.g., donepezil, galantamine, rivastigmine)
• aclidinium
• alcohol
• amantadine
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• antihistamines (e.g., azelastine, cetirizine, doxylamine, diphenhydramine, hydroxyzine, loratadine, rupatadine)
• antipsychotics (e.g., cariprazine, chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• atropine
• barbiturates (e.g., butalbital, phenobarbital)
• benzodiazepines (e.g., alprazolam, diazepam, lorazepam)
• benztropine
• botulinum toxin
• brimonidine
• buprenorphine
• butorphanol
• cannabis
• chloral hydrate
• clidinium
• clonidine
• darifenacin
• diphenoxylate
• disopyramide
• domperidone
• efavirenz
• entacapone
• esketamine
• fesoterodine
• flibanserin
• flunarizine
• gabapentin
• general anesthetics (medications used to put people to sleep before surgery)
• glucagon
• glycopyrrolate
• guanfacine
• ipratropium
• kava kava
• ketamine
• lemborexant
• linezolid
• lithium
• magnesium sulphate
• methylene blue
• metoclopramide
• mirabegron
• mirtazapine
• monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, rasagiline, selegiline, tranylcypromine)
• narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone)
• nabilone
• nitroglycerin
• other muscle relaxants (e.g., baclofen, methocarbamol, orphenadrine)
• oxybutynin
• perampanel
• pizotifen
• pomalidomide
• potassium chloride
• pramipexole
• pregabalin
• propiverine
• prucalopride
• ropinirole
• rotigotine
• St. John's wort
• scopolamine
• seizure medications (e.g., clobazam, levetiracetam, primidone, topiramate, valproic acid)
• serotonin/norepinephrine reuptake inhibitors (SNRIs; e.g., desvenlafaxine, duloxetine, venlafaxine)
• selective serotonin reuptake inhibitors (SSRIs; e.g., citalopram, fluoxetine, paroxetine, sertraline, vortioxetine)
• sodium oxybate
• solifenacin
• tetrabenazine
• thiazide diuretics (water pills; e.g., hydrochlorothiazide, indapamide, metolazone)
• tiotropium
• tizanidine
• tolterodine
• trazodone
• tricyclic antidepressants (e.g., amitriptyline, doxepin, imipramine, nortriptyline)
• trihexyphenidyl
• trospium
• tryptophan
• umeclidinium
• valerian
• verapamil
• zolpidem
• zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.