Interactions of Taking Flexeril

Medicines that interact with cyclobenzaprine may either decrease its effect, affect how long it works for, increase side effects, or have less of an effect when taken with cyclobenzaprine. 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 cyclobenzaprine include:

    • anti-anxiety medications
    • anticonvulsants
    • antidepressants, such as amitriptyline, imipramine, nortriptyline
    • antihistamines that cause sedation, such as diphenhydramine
    • duloxetine
    • 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 methocarbamol
    • sleeping pills, such as zolpidem
    • some chemotherapy treatments
    • some medications used to treat mental illness, such as clozapine and thioridazine
    • topiramate.

Alcohol may worsen the side effects of cyclobenzaprine such as drowsiness and dizziness.

Note that this list is not all-inclusive and includes only common medications that may interact with cyclobenzaprine. You should refer to the prescribing information for cyclobenzaprine for a complete list of interactions.

What is the Tips of Taking Flexeril ?

  • Cyclobenzaprine may be taken with or without food.
  • Cyclobenzaprine should be taken in addition to rest and physical therapy.
  • The effective dosage of cyclobenzaprine varies between individuals. Take cyclobenzaprine exactly as directed by your doctor. Talk with your doctor if you experience any worrying side effects or cyclobenzaprine is not effective.
  • Cyclobenzaprine 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.
  • Cyclobenzaprine is likely to make you sleepy or impair your judgment time. 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 cyclobenzaprine.
  • Talk to your doctor or pharmacist before taking any other medications while you are taking cyclobenzaprine. 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.

What is the Advantages and Disadvantages of Taking Flexeril ?

1. Advantages

  • Relieves muscle spasms associated with acute, painful, musculoskeletal conditions.
  • Improves pain, tenderness, and range of motion associated with muscle spasms and increases a person’s ability to perform their day-to-day activities.
  • Cyclobenzaprine is the most studied skeletal muscle relaxant.
  • Relieves skeletal muscle spasm without interfering with muscle function.
  • The sedative effects of cyclobenzaprine may help those experiencing insomnia as a result of muscle spasms.
  • Long-lasting effects.
  • Cyclobenzaprine has not been associated with addiction; however, abrupt discontinuation may produce symptoms such as nausea, headache, and a general feeling of discomfort. The dosage of cyclobenzaprine is best tapered off slowly on discontinuation.
  • Generic cyclobenzaprine is available.

2. Disadvantages

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. This is a major side effect and it may impair reaction skills and affect a person’s ability to drive or operate machinery. Avoid alcohol
  • Other common side effects include dry mouth, fatigue, difficulty with urination, an increase in eye pressure, headache, dizziness, blurred vision, or nausea
  • Should only be used short-term (for periods of up to two to three weeks only)
  • Not effective for muscle spasms occurring as a result of cerebral or spinal cord disease, or in children with cerebral palsy
  • Cyclobenzaprine 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)
  • Cyclobenzaprine 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 cyclobenzaprine should be reduced in people with mild liver disease. It should not be taken by people with moderate-to-severe liver disease
  • Cyclobenzaprine may 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 increase in eye pressure).
  • Ineffective for muscle spasms due to brain injury or disease.
  • Elderly people may be more sensitive to the effects of cyclobenzaprine, and the dosage should be kept low if the benefits of using it in seniors outweigh the risks.

How Cyclobenzaprine (Generic Flexeril) Works ?

  • Cyclobenzaprine may be used to relieve muscle spasms.
  • Cyclobenzaprine relaxes muscles by reducing muscle hyperactivity via 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.
  • Cyclobenzaprine will not reduce muscle spasms due to central nervous system (CNS) disease, such as cerebral palsy.
  • Cyclobenzaprine belongs to a class of drugs known as muscle relaxants.

Cyclobenzaprine Pregnancy Warnings

This drug should be used during pregnancy only if clearly needed.

US FDA pregnancy category: B

Embryofetal development in rats and rabbits given approximately 3 and 15 times, respectively, the maximum recommended human dose (MRHD) was not adversely effected. Dams receiving this drug at doses 3 times or more the MRHD during pregnancy and lactation, had pups with decreased body weight and survival. There are no adequate and controlled studies in pregnant women.

US FDA pregnancy category B: Animal reproduction studies have failed to demonstrate a risk to the fetus and there are no adequate and well-controlled studies in pregnant women.

Cyclobenzaprine Breastfeeding Warnings

This drug has been shown to be excreted in rat milk and achieve concentrations in the milk which are 50% of those in the rat maternal plasma. As this drug is closely related to the tricyclic antidepressants, some of which are known to be excreted in human milk, use caution especially when other drugs that cause sedation are used simultaneously.

Caution is recommended.

Excreted into human milk: Unknown
Excreted into animal milk: Yes

The effects in the nursing infant are unknown.


How long does Flexeril stay in your system?

As an estimate then , after taking a dose of Flexeril it should be out of your system within 5.5 days to 16.5 days.

Flexeril has a long half life of between 1 and 3 days. This is the time it takes for your body to reduce the plasma drug levels by half. Flexeril is eliminated slowly from the body.

It usually takes around 5.5 x half-life for a drug to be eliminated from your system.

This is (5.5 x 1) 5.5 days to (5.5 x 3) 16.5 days for Flexeril.

However other factors to consider include:

    •  How much and how often you have taken the drug.
    •  Your metabolic rate – a slower metabolism will increase the time a drug remains in your system.
    •  Your age and health – older age and poor health will generally increase the time the drug stays in your system.
    •  Body mass – generally the bigger you are the longer a drug will remain in your system.

What other drugs will affect Flexeril?

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.

This list is not complete. Other drugs may interact with cyclobenzaprine, including prescription and over-the-counter medicines, vitamins, and herbal products. Not all possible drug interactions are listed here.

What you should know before you take Flexeril ?

What is Flexeril?

Flexeril is a muscle relaxant. It works by blocking nerve impulses (or pain sensations) that are sent to your brain.


Flexeril is used together with rest and physical therapy to treat skeletal muscle conditions such as pain, injury, or spasms.

Flexeril may also be used for purposes not listed in this medication guide.


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.

Before taking this medicine

You should not use Flexeril if you are allergic to cyclobenzaprine, or if you have:

      • a thyroid disorder;
      • heart block, heart rhythm disorder, congestive heart failure;
      • or if you have recently had a heart attack.

Flexeril is not approved for use by anyone younger than 15 years old.

Do not use Flexeril if you have taken an MAO inhibitor in the past 14 days. A dangerous drug interaction could occur. MAO inhibitors include isocarboxazid, linezolid, phenelzine, rasagiline, selegiline, and tranylcypromine.

Some medicines can interact with cyclobenzaprine and cause a serious condition called serotonin syndrome.  Be sure your doctor knows if you also take stimulant medicine, opioid medicine, herbal products, or medicine for depression, mental illness, Parkinson’s disease, migraine headaches, serious infections, or prevention of nausea and vomiting. Ask your doctor before making any changes in how or when you take your medications.

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.

Older adults may be more sensitive to the effects of this medicine.

Flexeril Dosage

Generic name: cyclobenzaprine hydrochloride


Dosage form: Tablets

For most patients, the recommended dose of FLEXERIL is 5 mg three times a day. Based on individual patient response, the dose may be increased to 10 mg three times a day. Use of FLEXERIL for periods longer than two or three weeks is not recommended.

Less frequent dosing should be considered for hepatically impaired or elderly patients