Is Flexeril Addictive? + Uses, Drug Interactions, Side Effects

Flexeril is the brand name of a drug called cyclobenzaprine that is part of a class of drugs called skeletal muscle relaxants.

This medication works by blocking nerve impulses that are sent to the brain. It does not have any activity on the central nervous system nor does it have any action within the neuromuscular junctions (a synapse between a skeletal muscle and a motor neuron).


It is typically used (along with rest and physical therapy) to relieve muscle spasms. This helps reduce stiffness, pain, or discomfort caused by injuries or strains to the muscles.

Note – this medication is not designed for long-term use, and sufferers should follow the regimen provided by their physician.

Additionally, it is prescribed off-label to treat fibromyalgia, a common and complex chronic pain disorder that causes widespread pain. In addition to widespread pain, individuals with fibromyalgia may experience:

  • headaches;
  • increased sensitivity to pain;
  • a digestive condition which causes stomach bloating and pain (irritable bowel syndrome);
  • problems with mental processes, like – problems with concentration and memory;
  • difficulty sleeping (insomnia);
  • muscle stiffness;
  • extreme tiredness (fatigue).

It is not known exactly why some individuals develop fibromyalgia, but it is likely that a number of factors are involved. They include:

  • emotional stress – it can create long-reaching effects the body deals with for years. Also, it has been strongly associated with post-traumatic stress disorder;
  • trauma – individuals who experience physical trauma may develop fibromyalgia;
  • genetics – according to some studies, genetic mutations may play a role in developing this condition;
  • infections – prior illnesses may make some symptoms of this condition worse.


This medication comes as an extended-release capsule and a tablet to take by mouth. The extended-release capsule is typically taken without or with food once per day. The tablet is typically taken without or with food 3 times per day.

Important note – do not take this medication for more than 21 days without talking to your healthcare provider.

Side Effects And Precautions Of Cyclobenzaprine

Common side effects may include:

  • tired feeling;
  • dry throat;
  • dry mouth;
  • gas;
  • blurred vision;
  • muscle weakness;
  • constipation;
  • diarrhea;
  • nausea;
  • stomach pain;
  • loss of appetite;
  • dizziness;
  • drowsiness.

Rare side effects may include:

  • fainting;
  • uneven heartbeats;
  • sudden and severe headaches;
  • feeling light-headed;
  • fast heartbeat;
  • balance problems;
  • confusion;
  • weakness on one side of the body;
  • vision problems;
  • lack of coordination;
  • problems with speech;
  • weakness;
  • pain spreading to the shoulder or arm;
  • yellowing of the skin or eyes;
  • sweating;
  • clay-colored stools;
  • chest pain;
  • seizure (convulsions);
  • hallucinations (seeing things);
  • dark urine;
  • unusual thoughts;
  • low fever;
  • easy bruising or bleeding.

It can also cause a life-threatening condition called serotonin syndrome. This happens when drugs cause too much serotonin (a monoamine neurotransmitter) to build up in the human body. Symptoms of serotonin syndrome usually start within hours of taking a new drug which affects serotonin levels. They may include:

  • headaches;
  • confusion;
  • tremor;
  • restlessness;
  • rapid heart rate;
  • agitation;
  • heavy sweating;
  • dilated pupils;
  • diarrhea;
  • goosebumps;
  • shivering;
  • twitching muscles or loss of muscle coordination;
  • vomiting;
  • nausea;
  • changes in blood pressure.

Milder forms of serotonin syndrome may go away within a day of stopping the drugs which cause symptoms and, occasionally, by taking medicines which block serotonin.


Due to the fact that there are no adequate and well-controlled studies in pregnant women, talk to your healthcare provider before using this medicine. Also, it is not known whether it passes into breast milk or if it could harm your baby.

Alcohol Interaction

This drug may boost the effects of alcohol and will increase the sedative effects of both, causing dizziness and sleepiness. In addition, the side effects are increased for adults over 65 years because aging slows down the body’s capacity to metabolize alcohol, hence, it stays in a person’s body longer.

Moreover, individuals with hepatic impairment are usually more susceptible to medicines with potentially sedating effects.

Drug Interactions

Many drugs can interact with this medication. Therefore, tell your healthcare professional if you are using:

  • glycopyrrolate, a medication of the muscarinic anticholinergic group;
  • scopolamine, a medication used to treat postoperative nausea and motion sickness;
  • guanethidine, an antihypertensive medicine that reduces the release of catecholamines;
  • methscopolamine, a medicine that is used with other medication drugs to treat a peptic ulcer;
  • mepenzolate, a post-ganglionic parasympathetic inhibitor;
  • dimenhydrinate, an over-the-counter drug used to treat nausea and motion sickness;
  • tramadol (Ultram);
  • benztropine, an anti-Parkinson’s agent and anticholinergic;
  • atropine (Donnatal);
  • irritable bowel medications, like – propantheline (Pro-Banthine), hyoscyamine (Cystospaz, Anaspaz, Levsin), or dicyclomine (Bentyl);
  • a bronchodilator, like – tiotropium (Spiriva) or ipratropium (Atrovent);
  • urinary drugs, like – solifenacin (Vesicare), tolterodine (Detrol), oxybutynin (Oxytrol, Ditropan), flavoxate (Urispas), or darifenacin (Enablex).

Also, do not take this medicine if you have used a monoamine oxidase inhibitors within the past 2 weeks because life-threatening side effects can occur. Monoamine oxidase inhibitors include – selegiline (Emsam, Eldepryl), phenelzine (Nardil), tranylcypromine (Parnate), or isocarboxazid (Marplan). Other medicine may interact with this drug, including herbal and vitamin products.

Is Flexeril Addictive?

This medication is not considered to be physically addictive in the way that narcotic painkillers are. However, it is possible to become psychologically dependent on this medicine. This actually means that you may feel like you need to use this medicine to feel pain-free, particularly if you have been using it for over a month.


At higher doses, this medicine may cause a neurologic condition in which the patients lose control of their muscle movements, called ataxia. Also, when it is abused, it can induce moderate anticholinergic effects, meaning that it leads to an increased parasympathetic activity in the body. This can lead to mental and physical impairment.


It is recommended to store this medicine at 25°C (77°F).

Image credit – Shutterstock & Getty

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