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Side Effects of Flexeril

author image Susan Landis-Steward
Susan Landis-Steward has been a print journalist and editor since 1985, writing for "The Reflector," "The Multnomah Village Post," "The Evergreen Messenger" and "The Oregonian." She has won numerous awards for her reporting and has been published in top academic journals. Landis-Steward has a Master of Science in writing from Portland State University.
Side Effects of Flexeril
A father sits with his son, who has cerebral palsy byt the side of the lake. Photo Credit jarenwicklund/iStock/Getty Images

Flexeril, or cyclobenzaprine, is commonly used as a muscle relaxant and to help alleviate pain from sprains, muscle injuries and other conditions that cause muscle stiffness and pain. It relieves muscle spasms and allows relaxation and sleep.

Flexeril has also been found helpful in treating spasticity from cerebral palsy and other cerebral and spinal cord conditions. It does, however, have several side effects.


Flexeril works by blocking pain signals sent from your nerves to your brain. It is used in conjunction with rest and physical therapy. Flexeril is closely related to amitriptyline and imipramine, both tricyclic antidepressants.

Minor Side Effects

Dry mouth, blurred vision, daytime drowsiness, loss of appetite, nausea or stomach pain, muscle weakness, diarrhea or constipation, and dizziness are some of the common symptoms of Flexeril. Contact your physician if these are troublesome.

Drowsiness, dry mouth, dizziness, fatigue and headaches are the most commonly reported side effects, according to the website RxList.

Many patients also experience a morning "hangover" if they only take this medication at bedtime. Avoid driving a car or operating heavy machinery, and be aware that your mental focus may be impaired.

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Serious Side Effects

Flexeril can cause serious side effects requiring emergency intervention, according to Drugs.com. Symptoms include a racing or pounding heartbeat, chest pain, numbness or weakness, confusion with weakness and lack of coordination. Other symptoms include severe nausea, stomach pain, jaundice and seizures. Hallucinations and unusual thoughts or behavior are possible. Contact your physician or advice nurse immediately if you experience any of these problems.

Allergic Reactions and Overdose

Hives, problems breathing or swelling of your face or mouth or throat are symptoms of a serious allergic reaction. If you are having problems breathing or if symptoms are worsening rapidly, call 911.

Symptoms of overdose include severe drowsiness, racing heartbeat, hallucinations, chest pain, seizures, slurred speech or muscle stiffness with fever and sweating. Contact poison control or emergency room if you suspect an overdose.

Drug Interactions

Flexeril has numerous drug interactions, according to Drugs.com. Make sure your doctor is aware of all medications you are taking. Among the drugs with known interactions with Flexeril are atropine, benztropine, Dramamine, Atrovent, tramadol, and many medications used to treat bladder and urinary conditions. Medications used for irritable bowel syndrome also often interact negatively with Flexeril.


Flexeril enhances the effects of alcohol, barbiturates and central nervous system depressants, according to RxList.

Patients taking MAO inhibitors should not take Flexeril as it may have life-threatening interactions.

Discuss this drug with your physician before taking if you had a recent heart attack or have liver disease, congestive heart failure, glaucoma or hyperthyroidism.


Flexeril is usually prescribed as a short-term medication and should not be taken for longer than three weeks unless your physician recommends it.

Flexeril passes into breast milk so you should discuss its use with your pediatrician before breastfeeding.

Because this drug causes drowsiness which can be extreme in some patients, discuss its use with your doctor if you take anti-anxiety drugs, sleep sedatives, narcotic pain relievers, tranquilizers or psychiatric medications.

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