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Back Pain & Osteoporosis Library


Brand Name: Flexeril
Drug Class: Tricyclic antidepressant
Available in: Tablets
Available OTC? No
As Generic? Yes

Side Effects

Serious: Unusual heartbeat (racing, pounding, or fluttering), confusion, seizures, hallucinations.

Common: Drowsiness, dry mouth, dizziness.

Less Common: Fatigue or excessive tiredness, weakness, nausea, constipation, heartburn, unpleasant bitter or metallic taste in mouth, vision problems, headache, restlessness, nervousness, difficulty urinating, unusual bleeding or bruising.

Principal Uses

To relieve painful, temporary muscle stiffness and spasms. It is not used for stiffness and spasms due to serious, chronic illnesses of the nervous system and muscles, such as spinal cord injury or cerebral palsy.

How the Drug Works

Cyclobenzaprine appears to work by decreasing nerve impulses from the brain and spinal cord that lead to tensing or tightening of muscle fibers.


Adults and teenagers 15 years of age and older: Usual dose is 10 mg, 3 times a day, which may be increased by your doctor to a maximum total dose of no more than 60 mg per day. Children and teenagers up to 15 years of age: Consult pediatrician.

Onset of Effect

Within 1 hour. The maximum effect may require 1 to 2 weeks of therapy.

Duration of Action

12 to 24 hours following a single dose.

Dietary Advice

Dry mouth is a common complaint with muscle relaxants; maintain adequate fluid intake and suck on ice chips if desired.


Store in a tightly sealed container away from heat and direct light. Keep it away from moisture and extremes in temperature.

If You Miss a Dose

Take it as soon as you remember. If it is near the time for the next dose, skip the missed dose and resume your regular dosage schedule. Do not double the next dose.

Stopping the Drug

You should take it as prescribed for the full treatment period, but you may stop if you are feeling better before the scheduled end of therapy.

Prolonged Use

Therapy with cyclobenzaprine is usually completed within 14 to 21 days. Do not take cyclobenzaprine for a longer period without your doctor's approval. Muscle pain and stiffness that does not improve within 14 to 21 days may require a more thorough evaluation.


Over 60: Adverse reactions may be more likely and more severe in older patients.

Driving and Hazardous Work: The use of cyclobenzaprine may impair your ability to perform such tasks safely; use caution.

Alcohol: Avoid alcohol.

Pregnancy: Adequate studies of cyclobenzaprine use during pregnancy have not been done; discuss the relative risks and benefits with your doctor.

Breast Feeding: Cyclobenzaprine may pass into breast milk; caution is advised. Consult your doctor for advice.

Infants and Children: Cyclobenzaprine is not recommended for use by children under the age of 15.

Special Concerns: Cyclobenzaprine is not meant to be used as the only treatment for sore or stiff muscles. It should be accompanied by bed rest, physical therapy, and other measures to relieve discomfort, such as the application of heat or ice packs (as suggested by your physician).


Symptoms: Severe mental confusion, agitation, impaired concentration, difficulty walking or standing, dilated pupils, severe drowsiness, coma.

What to Do: Call emergency medical services (EMS), your doctor, or the nearest poison control center immediately.

Drug Interactions

Consult your doctor for specific advice if you are taking sedatives, tranquilizers, or other medications that cause drowsiness (including alcohol); tricyclic antidepressants; or MAO inhibitors.

Food Interactions

No known food interactions.

Disease Interactions

Consult your doctor if you have a history of any of the following: glaucoma, difficult urination, prostate problems, heart disease, or overactive thyroid.

From The Johns Hopkins Consumer Guide to Drugs. You can order this book now on our secure server.


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