Cyclobenzaprine

What is cyclobenzaprine?

Cyclobenzaprine is an oral medication available by prescription only and is sold under its generic name and the brand name Amrix.

As a muscle relaxant, cyclobenzaprine reduces the affected muscles’ hyperactivity, allowing them to relax, and reduces the nerve pain signals to the brain. This medication is used in conjunction with rest and physical therapy to treat and manage the pain, spasms, and discomfort that often accompany musculoskeletal injuries or conditions.¹

Doctors sometimes prescribe cyclobenzaprine off-label for other conditions, such as temporomandibular disorders and fibromyalgia, but the drug is not indicated by the US Food and Drug Administration (FDA) for these uses.²

What is cyclobenzaprine used to treat?

Cyclobenzaprine is commonly prescribed after injuries affecting the muscles in the body, such as sprains and strains, varying in severity. While the medicine does not reduce inflammation or heal the injury directly, it relieves discomfort and pain and reduces spasms during the healing process, allowing the patient to focus on rest and recovery. Cyclobenzaprine is only prescribed as short-term treatment and is intended for acute musculoskeletal conditions.³ ⁴

Dosage forms and strengths

Cyclobenzaprine is available in oral tablet and extended-release capsule forms in the following strengths:⁵ ⁶

• Tablets (generic): 5mg, 7.5mg, 10mg

• Extended-release capsules (generic, Amrix): 15mg, 30mg 

Patients taking the tablet form usually take 5mg every eight hours. However, if necessary, the prescribing doctor may increase the dose to 7.5mg or 10mg every eight hours.

Those taking the extended-release capsule form of cyclobenzaprine may take a single 15mg or 30mg dose daily. This form is not recommended for elderly patients.

How do you take cyclobenzaprine?

Take cyclobenzaprine precisely as prescribed by your doctor. You should swallow each tablet or capsule whole without chewing, crushing, or splitting it. However, if you struggle with swallowing pills, you can carefully break open the extended-release capsule, mix its contents into a spoonful of applesauce, and swallow the entire mixture immediately without chewing. If you choose this route, follow the applesauce mixture with a glass of water.⁷

You can take this drug with or without food. Take it exactly as prescribed, do not change your dose or schedule without consulting your doctor. Cyclobenzaprine should not be used for longer than three weeks. If you feel you need treatment beyond that, ask your doctor about appropriate treatment options.⁸

Seeing results

How soon you see results will depend on the form of cyclobenzaprine you take. The immediate-release tablets can take effect within 30–60 minutes. The extended-release tablets take a little longer to work, but the effects will last longer.

Who should not take cyclobenzaprine?

Cyclobenzaprine is not suitable for everyone. The drug is not recommended for elderly patients or children under 15 years, and it is contraindicated in the following groups:⁹

• People who are hypersensitive to any of the drug’s active or inactive ingredients

• Those who are taking monoamine oxidase inhibitors (MAOIs) or have taken them within the past 14 days

• People with certain heart conditions (myocardial infarction, heart block or conduction disturbances, arrhythmias, or congestive heart failure)

• Individuals diagnosed with hyperthyroidism

The drug is not recommended for people who:

• Are taking any other serotonergic drugs (see Drug interactions)

• Have been diagnosed with hyperthyroidism

• Have liver disease

Additionally, cyclobenzaprine should be prescribed cautiously in people with a history of urine retention, increased intraocular pressure, angle-closure glaucoma, and those currently taking anticholinergic drugs.

Potential side effects of cyclobenzaprine

The most common side effects reported by patients taking cyclobenzaprine include the following:¹⁰

• Dizziness

• Drowsiness, fatigue, or lack of energy

• Feeling weak

• Dry mouth

• Nausea

• Constipation

• Indigestion

• Unpleasant taste

• Headache

• Blurred vision

• Confusion

If these symptoms become severe or persist beyond a few days of starting the drug, you should consult your doctor.

Less common and potentially severe side effects include:

• Whole body effects, such as malaise, fainting, chest pain, and edema (swelling)

• Digestive effects, including gastrointestinal pain or inflammation, vomiting, abnormal liver functions, inflammation of the liver, or tongue edema

• Cardiovascular effects, such as a fast or irregular heart rate, palpitations, arrhythmia, high or low blood pressure, heart attack, and stroke 

• Endocrine effects, particularly antidiuretic hormone syndrome, a condition in which the body makes too much of this hormone, leading to water retention and edema

• Metabolic, nutritional, or immune effects, including blood sugar and weight changes

• Blood and lymphatic system effects, such as leukopenia (too few leukocytes in the blood) and low platelet count

• Musculoskeletal effects, including unexplained muscle aches and pains

• Respiratory effects, particularly shortness of breath

• Urogenital effects, including changes in urinary frequency, difficulty urinating, impotence, swelling of the testis, and gynecomastia (increased breast size in men)

• Skin effects, particularly increased sensitivity to UV light, increased sweating, and hair loss

• Nervous system and psychiatric effects, including seizures, tremors, serotonin syndrome, Bell’s palsy, disorientation, hallucinations, psychosis, depressed mood, changes in libido, and anxiety

• Other effects, including loss of taste and tinnitus (ringing in the ears)

Note that these lists of side effects are not exhaustive. If you experience anything unusual while taking cyclobenzaprine, consult your doctor. If you experience any severe side effects, seek immediate medical attention.

People who take cyclobenzaprine outside the parameters of treatment set out by their doctor face an increased risk of developing severe, potentially fatal side effects.

Overdose

If you experience any symptoms of an overdose or believe you or someone else may have taken too much cyclobenzaprine, call 911 or go to your nearest emergency room. An overdose of cyclobenzaprine could be fatal.

Possible signs and symptoms of an overdose include:¹¹

• Severe drowsiness

• Rapid heartbeat

• Agitated state

• Hallucinations

• Confusion

• Altered speech

• Seizure or convulsions

• Nausea or vomiting

• High blood pressure

• Coma

Allergy information

Anaphylaxis is a rare but life-threatening allergic reaction that can occur if you are allergic to cyclobenzaprine or any of the medication’s contents. If you experience symptoms of anaphylaxis, such as the closing of the throat, rapid heartbeat, tongue or face swelling, chest pain, or wheezing, call 911 immediately.

Long-term use of cyclobenzaprine

Cyclobenzaprine should only be taken for short periods, up to a maximum of three weeks. There is little research and evidence that using this medication beyond that period is effective or safe. In most cases, the muscle sprains or injuries for which cyclobenzaprine was prescribed will heal during this period. If you feel you need treatment beyond three weeks, ask your doctor which treatment options are suitable.

Cyclobenzaprine in pregnancy and breastfeeding

The US FDA designated cyclobenzaprine as a category B drug.¹²

Studies in humans using cyclobenzaprine in pregnancy have not identified a drug-associated risk of major congenital disorders, miscarriage, or adverse maternal or fetal outcomes. However, in animal studies, taking cyclobenzaprine during pregnancy or lactation in doses three times the maximum human doses lead to decreased fetal body weight and survival.¹³

It is not known if cyclobenzaprine passes through breast milk, but similar drugs, such as tricyclic antidepressants, are excreted in human breast milk, so caution must be taken if breastfeeding while taking this medication. It is essential to inform your doctor if you plan to breastfeed while taking cyclobenzaprine, so they can weigh the benefits of taking this drug against any potential risks.¹⁴

Missed doses

If you miss a dose of cyclobenzaprine, take it as soon as you remember unless it’s nearly time for your next scheduled dose. If you’re scheduled to take another dose soon, skip the missed dose and continue your regimen as prescribed. Never double your dose to make up for a mixed one, as doing so could increase your risk of an overdose or other severe adverse effects.¹⁵

Drug interactions

Do not take cyclobenzaprine if you are taking MAOIs, which are commonly used to treat depression. The interaction between MAOIs and cyclobenzaprine can be fatal.¹⁶

Other drugs known to interact with cyclobenzaprine include:

• Selective serotonin reuptake inhibitors (SSRIs)

• Selective norepinephrine reuptake inhibitors (SNRIs)

• Tricyclic antidepressants (TCAs)

• Tramadol

• Meperidine

• Verapamil

• Bupropion

Other interactions may occur. Before taking cyclobenzaprine, speak with your doctor about all medications (prescribed and over-the-counter), supplements, and herbs you take regularly or occasionally.

Can I drink alcohol while taking cyclobenzaprine?

You should not drink alcohol while taking cyclobenzaprine. Taking cyclobenzaprine in combination with alcohol can exacerbate the effects of both substances, potentially leading to severe side effects.

What to discuss with your doctor before starting cyclobenzaprine?

A number of factors contribute to the safety and effectiveness of medications. Before starting treatment with cyclobenzaprine, discuss the following topics with your doctor. Your doctor will let you know if the drug is appropriate for you and can monitor your progress if necessary. Inform your doctor of the following:

• All medications (prescribed or over-the-counter) and supplements you take regularly or occasionally

• Any current or past mental health issues

• Any history of drug abuse, including prescription drug misuse

• Your medical history and any conditions you have, including cardiovascular, neuromuscular, liver, kidney, thyroid, prostate, or eye health concerns

• Current or planned pregnancies or plans to breastfeed

• Your alcohol consumption

Stopping cyclobenzaprine

Unless your planned treatment course has ended or you need to stop taking cyclobenzaprine due to severe side effects or an allergic reaction, speak with your doctor before stopping. Most people who stop taking the drug as prescribed will experience little to no effects. It is not necessary to taper the dosage as the medication is used for short periods. Some people have reported symptoms, such as headache and nausea when discontinuing the drug after taking it for an extended time. These symptoms typically resolve over time without intervention.

If cyclobenzaprine is misused, taken longer than prescribed, or taken in combination with other drugs causing an interaction, withdrawal symptoms are possible. Speak with your doctor or a substance abuse counselor if you believe you’re suffering from withdrawal after discontinuing cyclobenzaprine.

Drug approval history

1977: Cyclobenzaprine earns US FDA approval¹⁷

2007: The extended-release capsule form is approved¹⁸

Tips for taking cyclobenzaprine

• Set alarms to help you remember your next dose.

• Keep a log of all medications and supplements you take.

• Do not add a new prescription or over-the-counter medicines without asking your doctor about potential interactions.

• Avoid storing your medication near sources of extreme cold or heat.

Frequently asked questions

Should you drive while taking cyclobenzaprine?

Some people feel drowsy, dizzy, or confused while taking cyclobenzaprine, especially when starting treatment or increasing the dose. Assess your body’s handling of the drug before you engage in potentially dangerous activities that demand alertness.

How does cyclobenzaprine make you feel?

Due to its effects on the brain and central nervous system, cyclobenzaprine can make you feel relaxed. Some may describe the feeling when taking cyclobenzaprine as similar to a sedative.

Can you overdose on cyclobenzaprine?

It is possible to overdose on cyclobenzaprine. Accidental overdoses can occur if doses are combined or if the medication is taken in conjunction with other substances with similar properties and ingredients. A cyclobenzaprine overdose is a medical emergency. If you suspect you or someone else has taken too much cyclobenzaprine, seek urgent medical care.