How Long Does Flexeril Stay in Your System?

Published August 1st, 2020 by Bridget Reed
Fact Checked by
Erik Rivera
Medically Reviewed:
Dr. Angel Rivera
Updated Date: May 17th, 2021

As much as we might try to avoid them, nearly everyone suffers from some type of muscular injury during their lifetime even before their half-life milestone, whether it is a muscle sprain, and strain, or chronic back pain caused by an injury. Muscle relaxers are commonly prescribed in these situations in order to help patients go about their daily activities and gently exercise the injured area in order to treat the source of the pain. One of the most popular muscle relaxers, Flexeril, can be taken for up to three weeks in the event of injury to the musculoskeletal system, but how long does Flexeril stay in your system

What is Flexeril?

Flexeril, also known under the generic name cyclobenzaprine, was first approved by the DEA and the U.S. Food and Drug Administration (FDA) in 1977. The medication belongs to a class of drugs called skeletal muscle relaxants, and the drug works on the central nervous system to relax the muscles. Although Flexeril is classified as a skeletal muscle relaxant, it works in a fashion similar to antidepressants, specifically tricyclic antidepressants, because it acts on the central nervous system. Flexeril is intended for short term use of two to three weeks and is available only in the generic form of the drug at this time, as all brand names of the medication have been discontinued. However, most people still refer to cyclobenzaprine as Flexeril.

What is Flexeril used to treat?

Flexeril is predominantly used to relieve pain, discomfort, detox, and stiffness that is caused by acute injury, including sprains, and strains, to the muscles. Flexeril relaxes the muscles that are tense and painful due to injury, which allows the patient to perform rehabilitative exercises that treat the injury. Additionally, Flexeril helps patients perform normal activities, such as sleeping and working, without the pain caused by their injury. Flexeril is used in conjunction with rest and physical therapy, because taking the medication on its own will not resolve the root cause of the muscle spasms and pain. The medication is generally intended for short term use of two to three weeks during the healing process. 

How does Flexeril work?

The main effect of Flexeril is relaxation of the muscles to prevent spasms and reduce pain. The medication works by reducing muscle hyperactivity that causes spasms by working on the alpha and gamma motor systems in the body. These two systems are made up of nerve fibers that connect directly to the muscles in the body and direct them to contract. Flexeril directs the brain, and to a lesser extent, the spinal cord,  to relax the muscles, and does not work directly on the muscles themselves.

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How long does Flexeril stay in your system?

After taking Flexeril, you’ll begin to notice the effects of the medication within approximately 20 to 30 minutes. Levels of Flexeril in your system peak approximately three to four hours after taking the medication, after which time the effects begin to diminish. Most people feel the effects of Flexeril for about four to six hours. However, just because you stop feeling the effects of Flexeril does not mean that the medication has left your system. Flexeril is detected in a urine sample for anywhere from three to eight days after taking your last dose, and it appears in a blood test and drug test for up to 3.75 days after it is last ingested. Flexeril stays in your saliva for 36 hours after use, and it is unknown how long it stays in your hair. However, there are no hair tests or hair follicle tests currently on the market for Flexeril.

How much does Flexeril cost?

Flexeril has been on the market since 1977, and the generic form of the medication, cyclobenzaprine, is available from a number of different manufacturers, which helps to keep prices low. A prescription of 30 10-mg tablets of the generic form of the medication can be purchased for less than 9 dollars, and most people do not take the medication for more than 2 to 3 weeks. Cyclobenzaprine is covered by most types of health insurance, including Medicare and Medicaid; no brand name forms of the medication are still being manufactured. Pharmacy discount programs like USA Rx offer discounts on all FDA-approved prescription medications, including both brand name and generic versions of the medication. These programs are free to register and do not have any eligibility requirements, so everyone can save on their prescriptions regardless of their insured status. 

What are the side effects of Flexeril?

Most side effects associated with Flexeril do not require medical attention, but you should tell your doctor about any side effect that is particularly bothersome, gets worse, or does not go away after a few days. The most common side effects associated with Flexeril include:

  • Drowsiness
  • Headache
  • Dry mouth
  • Nausea
  • Tiredness
  • Dizziness
  • Upset stomach
  • Constipation

Serious side effects that require immediate medical attention include:

  • Fast or irregular heartbeat 
  • Pain spreading to the jaw or shoulder
  • Slurred speech
  • Chest pain or pressure
  • Sudden numbness or weakness, particularly on one side of the body
  • Balance problems

How do I use Flexeril?

Flexeril should be taken at the same time every day and should not be taken for more than three weeks because of its extended-release. Because Flexeril does not heal any injuries or conditions and simply causes the muscles to relax, the medication is usually prescribed in conjunction with physical therapy or other addiction treatment that helps address the cause of the condition. In order to avoid the risk of dependency, patients should take only the dosage prescribed. Your doctor may change the dose of your medication as your symptoms improve. 

What risks are associated with Flexeril?

Flexeril is helpful for many people trying to overcome musculoskeletal conditions, but it is not right for everyone. If you are under the age of 15 or you have a history of any of the following medical conditions, you should not take Flexeril:

  • Allergy to cyclobenzaprine
  • Thyroid disorder
  • Heart block, congestive heart failure, or heart rhythm disorder
  • Recent heart attack

Flexeril may interact with certain prescription drugs and cause a dangerous reaction. People taking any of the following types of medication should speak to their doctors before taking Flexeril:

  • MAO inhibitors, including:
    • Isocarboxazid
    • Linezolid
    • Phenelzine
    • Rasagiline
    • Selegiline
    • Tranylcypromine
  • Stimulant medication
  • Opioid medication
  • Herbal products
  • Medication for depression
  • Medication for mental illness
  • Medication for Parkinson’s disease
  • Medication for migraine headaches
  • Medication for serious infections
  • Medication for the prevention of nausea or vomiting

People with certain medical conditions may be able to take Flexeril but may need to take it at a lower dose or certain time of day. These medical conditions include:

  • Liver disease
  • Enlarged prostate
  • Glaucoma
  • Problems with urination

Can women who are pregnant or breastfeeding take Flexeril?

Flexeril is categorized by the FDA as a Category B medication for pregnant women, meaning that existing studies performed on animals have not indicated any evidence that taking the medication while pregnant results in harm to the fetus or impaired fertility. No studies have been performed on humans, so patients should take the medication only when benefits clearly outweigh the risks. The use of Flexeril in nursing women has not been conclusively studied. However, other similar medications, including tricyclic antidepressants, have been shown to secrete into breastmilk. Therefore, nursing mothers should speak to their doctors about taking Flexeril while nursing in order to determine if the benefits outweigh the risks. 

Is it possible to overdose on Flexeril?

Flexeril works on the central nervous system in a way that is similar to a class of drugs called tricyclic antidepressants. Although the medication does not provide a high or euphoric feeling, some people do abuse the medication due to the relaxing effects it produces. Some people begin to take more Flexeril than is prescribed to increase the feeling of relaxation provided by Flexeril, which can lead to overdose. Signs of Flexeril overdose include:

  • Chest pain
  • Hallucinations
  • Slurred speech
  • Rapid heartbeat
  • Vomiting
  • Difficulty breathing
  • Extreme drowsiness

People are more likely to overdose on Flexeril when the medication is combined with other drugs, particularly those that depress the central nervous system, such as alcohol or benzodiazepines. Although Flexeril was previously considered non-addictive, it is now believed that Flexeril addiction is possible. Signs of Flexeril addiction include:

  • Taking Flexeril for longer than prescribed or after the need for the medication has been resolved
  • Spending a large part of the day thinking about Flexeril and how to get more or when to use it
  • Faking symptoms or injury to get more Flexeril prescriptions
  • Taking more of the medication to produce the same effects
  • Taking Flexeril constantly and being unable to stop
  • Sudden changes in behavior, physical appearance, or hygiene
  • Combining Flexeril with another medication or substance in order to enhance its effects. 

People who are addicted to Flexeril may experience slight withdrawal symptoms when they stop taking the drug, although these are typically not severe. Withdrawal symptoms include nausea, headache, fatigue, and cravings for the medication. 


Published August 1st, 2020 by Bridget Reed
Fact Checked by
Erik Rivera
Medically Reviewed:
Dr. Angel Rivera
Updated Date: May 17th, 2021

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