Flexeril: 7 things you should know
Medically reviewed by Carmen Fookes, BPharm. Last updated on Nov 6, 2020.
1. How it works
- Flexeril is a brand (trade) name for cyclobenzaprine. Cyclobenzaprine relaxes muscles by reducing muscle hyperactivity through an action on both gamma and alpha motor systems (these are nerve fibers that directly connect with skeletal muscle and are responsible for muscle contraction). Cyclobenzaprine acts primarily through the brain stem rather than the spinal cord and does not act directly on skeletal muscle.
- Flexeril will not reduce muscle spasm due to central nervous system (CNS) disease, such as cerebral palsy.
- Flexeril belongs to a class of drugs known as muscle relaxants.
- May be used for the short-term relief of muscle spasm associated with acute, painful, musculoskeletal conditions.
- Improves pain, tenderness, and range of motion associated with muscle spasm and increases a person's ability to perform their day-to-day activities.
- Relieves skeletal muscle spasm without interfering with muscle function.
- The sedative effects of Flexeril may help people sleep who are experiencing insomnia as a result of muscle spasm.
- Flexeril's effects are long-lasting.
- Flexeril has not been associated with addiction; however, abrupt discontinuation may produce symptoms such as nausea, a headache, and a general feeling of discomfort. The dosage of Flexeril is best tapered off slowly on discontinuation.
- Flexeril is available as a generic under the name cyclobenzaprine.
If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:
- Sedation is a major side effect that may impair reaction skills and affect a person's ability to drive or operate machinery. Alcohol should be avoided.
- Dry mouth, tiredness, dizziness, headache, difficulty with urination, nausea, an increase in eye pressure, and blurred vision have also been reported.
- Heart palpitations, seizures, and an increased risk of a heart attack have rarely been associated with Flexeril.
- Effects may be similar to those seen with tricyclic antidepressants (TCAs) as Flexeril is structurally related to TCAs.
- Abrupt cessation of Flexeril may cause sickness, headache, and tiredness; however, these are not indicative of addiction.
- Should only be used short-term (for periods of up to two to three weeks only).
- Not effective for muscle spasm occurring as a result of cerebral or spinal cord disease, or in children with cerebral palsy.
- Flexeril should never be given within 14 days of monoamine oxidase (MAO) inhibitor antidepressants, as the combination may be fatal.
- Interaction with other drugs that also increase serotonin (such as antidepressants, tramadol, St John's Wort, bupropion) may cause serotonin syndrome. Symptoms include mental status changes (such as agitation, hallucinations, coma, delirium), fast heart rate, dizziness, flushing, muscle tremor or rigidity, and stomach symptoms (including nausea, vomiting, and diarrhea).
- Flexeril may enhance the effects or side effects of tricyclic antidepressants (for example, amitriptyline and imipramine), alcohol, and other CNS depressants.
- May not be suitable for people with arrhythmias, heart block or conduction disturbances, heart failure, hyperthyroidism, or immediately following a heart attack.
- The dosage of Flexeril should be reduced in people with mild liver disease. It should not be taken by people with moderate-to-severe liver disease.
- Flexeril may also not be suitable for people with glaucoma or increased intraocular pressure, a history of urinary retention, or taking other drugs that also have anticholinergic side effects (anticholinergic side effects include constipation, blurred vision, and an increase in eye pressure).
- Elderly people may be more sensitive to the effects of Flexeril, and the dosage should be kept low if the benefits of using it in seniors outweigh the risks.
Notes: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. For a complete list of all side effects, click here.
- Flexeril may be taken with or without food.
- Flexeril should be taken in addition to rest and physical therapy.
- The effective dosage of Flexeril varies between individuals. Take Flexeril exactly as directed by your doctor. Talk with your doctor if you experience any worrying side effects or if Flexeril is not effective.
- Flexeril is usually only given for a maximum of two to three weeks. Your doctor may advise tapering off the dose slowly when it is time to discontinue it.
- Flexeril is likely to make you sleepy or impair your judgment time. This may be beneficial in aiding sleep; however, you should avoid operating machinery, driving, or performing tasks that require mental alertness while taking this medicine.
- Avoid alcohol while taking this medicine. Alcohol may potentiate the side effects of Flexeril.
- Talk to your doctor or pharmacist before taking any other medications while you are taking Flexeril. Contact your doctor urgently if you experience any mental status changes (such as agitation, hallucinations, coma, delirium), fast heart rate, dizziness, flushing, muscle tremor or rigidity, and stomach symptoms (including nausea, vomiting, and diarrhea).
- Tell your doctor if you have a heart condition, thyroid disease, liver disease, glaucoma, or a problem with urination before starting treatment.
6. Response and Effectiveness
- Some muscle-relaxing effects may be noted within 20 to 30 minutes of oral administration. The effects of Flexeril last for four to six hours. Flexeril is eliminated from the body relatively slowly (7 to 37 hours).
- 5mg of Flexeril is reportedly as effective as 10mg of Flexeril, with fewer side effects.
- Flexeril is ineffective in muscle spasm due to brain injury or disease.
Medicines that interact with Flexeril may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with Flexeril. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.
Common medications that may interact with Flexeril include:
- anti-anxiety medications
- antidepressants, such as amitriptyline, imipramine, nortriptyline
- antihistamines that cause sedation, such as diphenhydramine
- monoamine oxidase inhibitors, such as selegiline, isocarboxazid, or phenelzine (interaction may be life-threatening)
- opioid analgesics such as oxycodone and morphine
- other muscle relaxants such as cyclobenzaprine
- sleeping pills, such as zolpidem
- some chemotherapy treatments
- some medications used to treat mental illness, such as clozapine and thioridazine
Alcohol may worsen the side effects of Flexeril such as drowsiness and dizziness.
Note that this list is not all-inclusive and includes only common medications that may interact with Flexeril. You should refer to the prescribing information for Flexeril for a complete list of interactions.
Flexeril (cyclobenzaprine hydrochloride) [Package Insert]. Revised 10/2020. McNeil Consumer and Specialty Pharmaceuticals https://www.drugs.com/pro/flexeril.html
Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use Flexeril only for the indication prescribed.
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More about Flexeril (cyclobenzaprine)
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- Support Group
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- Drug class: skeletal muscle relaxants
- FDA Alerts (1)