Flexeril treats muscle spasms. It works by relaxing your muscles, which reduces muscle stiffness. It belongs to a group of medications called muscle relaxants. Flexeril is used together with rest and physical therapy to treat skeletal muscle conditions such as pain, injury, or spasms.

Dosage and direction
Flexeril is usually taken once daily for only 2 or 3 weeks. Follow all directions on your prescription label and read all medication guides or instruction sheets. Your doctor may occasionally change your dose. Take the medicine at the same time each day.

Precautions
To make sure Flexeril is safe for you, tell your doctor if you have ever had: liver disease; glaucoma; enlarged prostate; or problems with urination.
It is not known whether cyclobenzaprine will harm an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant.
It may not be safe to breast-feed while using this medicine. Ask your doctor about any risk.

Contraindications
You should not use Flexeril if you have a thyroid disorder, heart block, congestive heart failure, a heart rhythm disorder, or you have recently had a heart attack.
Do not use cyclobenzaprine if you have taken an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, or tranylcypromine.

Possible side effect
Get emergency medical help if you have signs of an allergic reaction to Flexeril: hives; difficult breathing; swelling of your face, lips, tongue, or throat.
Stop using Flexeril and call your doctor at once if you have: fast or irregular heartbeats; chest pain or pressure, pain spreading to your jaw or shoulder; or sudden numbness or weakness (especially on one side of the body), slurred speech, balance problems.
Seek medical attention right away if you have symptoms of serotonin syndrome, such as: agitation, hallucinations, fever, sweating, shivering, fast heart rate, muscle stiffness, twitching, loss of coordination, nausea, vomiting, or diarrhea.
Common Flexeril side effects may include: drowsiness, tiredness; headache, dizziness; dry mouth; or upset stomach, nausea, constipation.

Drug interaction
Using Flexeril with other drugs that make you drowsy can worsen this effect. Ask your doctor before using opioid medication, a sleeping pill, a muscle relaxer, or medicine for anxiety or seizures.
Tell your doctor about all your other medicines, especially: bupropion (Zyban, for smoking cessation); meperidine; tramadol; verapamil; narcotics; cold or allergy medicine that contains an antihistamine (Benadryl and others); medicine to treat Parkinson's disease; medicine to treat excess stomach acid, stomach ulcer, motion sickness, or irritable bowel syndrome; medicine to treat overactive bladder; or bronchodilator asthma medication.

Missed dose
Take the medicine as soon as you can, but skip the missed dose if it is almost time for your next dose. Do not take two doses at one time.

Overdose
Overdose symptoms may include severe drowsiness, vomiting, fast heartbeats, tremors, agitation, or hallucinations. Seek emergency medical attention. An overdose of cyclobenzaprine can be fatal.

Storage
Keep out of the reach of children. Store at room temperature between 15 and 30 degrees C (59 and 86 degrees F). Keep container tightly closed. Throw away any unused medication after the expiration date.