Cyclobenzaprine (Flexeril) Overview?
Cyclobenzaprine, once widely available under the trade name Flexeril and still available as the branded, extended-release formulation Amrix—is a muscle relaxant that is primarily used for the short-term treatment of muscle spasm and certain other painful musculoskeletal conditions.
As a skeletal muscle relaxant, cyclobenzaprine is ineffective for people with muscle spasticity of spinal cord or cerebral disease origin.1
Cyclobenzaprine is intended for relatively short-term use (in general, 2-3 weeks). Spasticity associated with acute musculoskeletal conditions is not typically long-lasting, and cyclobenzaprine has not been proven effective for periods longer than 2 weeks. The drug is most commonly used in conjunction with other forms of treatment, particularly physical therapy.1
The recommended dose of immediate-release cyclobenzaprine is 5 to 10mg, three times a day, while that for extended-release versions is 15 to 30 mg, once a day. Maximum daily dose for either form is 30 mg over the course of 24 hours. Taking more than recommended may result in adverse effects or overdose.
Can You Overdose on Cyclobenzaprine?
Yes, you can overdose on cyclobenzaprine, which is also called Flexeril. Some skeletal muscle relaxants (e.g., carisoprodol) have sedative properties so people may attempt to abuse a drug like cyclobenzaprine thinking that it will have similar sedating effects.
Cyclobenzaprine does make some users somewhat drowsy, and may be used in combination with other drugs to modify the subjective high that would be experienced with that substance alone. In fact, most abuse of this substance occurs in combination with other substances such as benzodiazepines, alcohol, or opioids.2
Abuse of muscle relaxants alone is uncommon; often, it involves other substances. The drug may be used to potentiate (intensify) the effects of alcohol, benzodiazepines, or opioids.3 This is concerning because, while rare, deadly overdose from cyclobenzaprine is more common when other substances like alcohol are involved.
If you’re taking Flexeril nonmedically for a high—with or without other drugs—treatment for substance abuse can prevent you from suffering a dangerous overdose.
What are the Signs of a Cyclobenzaprine Overdose?
The signs and symptoms of flexeril overdose can develop quickly and may include:6
- Rapid heart rate.
- High blood pressure.
- Slurred speech.
Rare but serious effects of a flexeril overdose may include:
- Abnormal heart rhythms.
- Chest pain.
- Cardiac arrest.
- Significant drop in blood pressure.
In overdose, there is also the slight potential for the development of a severe syndrome known as neuroleptic malignant syndrome.1 The symptoms associated with this syndrome include:4
- Severe rigidity of the muscles.
- Elevated body temperature.
- Pale or flushed skin.
- Rapid heart rate.
- High blood pressure, or rapidly changing blood pressure.
- Trouble swallowing.
- Inability to speak.
- Increasing numbers of white cells in the blood.
- Changing levels of consciousness.
The syndrome is also sometimes associated with rhabdomyolysis, a very serious condition that involves the breakdown of muscle tissues and the release of large protein molecules into the bloodstream.
The spilling of proteins (myoglobin) associated with rhabdomyolysis can lead to kidney injury.5 Neuroleptic malignant syndrome can be fatal if not treated quickly.4
Risk in the Elderly
Cyclobenzaprine’s plasma concentrations average 40% higher in the elderly, making these patients more at risk of the drug’s harmful effects. The drug is also eliminated more slowly in this age group.
Older adults may be more likely to experience confusion, hallucinations, adverse cardiac events, and to injure themselves (e.g., from falls). Physicians are often advised to avoid use of this drug in the elderly unless it is absolutely necessary and, if use is initiated, to start them on a lower dose.1,6,7
Treatment for Substance Abuse
Abuse of cyclobenzaprine is relatively rare but most often occurs in the context of other substance use. Polydrug abuse can cause serious harm, especially when the combination includes CNS depressing substances such as benzodiazepines and alcohol.
Severe CNS depression may result in significantly slowed breathing, oversedation, coma, and death.3 If you are unable to stop abusing one or more substance, it’s time to seek help. Admitting your substance use has gotten out of control can save your life.
Cyclobenzaprine withdrawal alone is not likely to be significantly distressing; symptoms include headache, nausea, and malaise.1 However, for those who are dependent on other drugs such as alcohol or benzodiazepines, withdrawal symptoms may be severe enough to warrant inpatient medical care.
Many treatment programs offer medical detoxification to address physical dependence in a safe environment with caring physicians and nurses who will work to alleviate symptoms and increase your comfort.
Post-detox, treatment will center around counseling and behavioral therapy (both individual and group) to uncover the maladaptive beliefs and behaviors that promote substance use and to develop new coping mechanisms that support recovery.
There is also a slight risk that abuse of Cyclobenzaprine or Flexeril can lead to serotonin syndrome. Serotonin syndrome occurs when you take medications that cause an excess of serotonin in your system. Since cyclobenzaprine is commonly prescribed for short term use to aid patients with muscle spasms or musculoskeletal conditions, those who are already using medication to manage separate conditions are at a higher risk of this condition.
Serotonin syndrome symptoms typically start to manifest within several hours of taking a new drug or increasing the dose of a drug you’re already taking. Symptoms of serotonin syndrome include:
- Muscle rigidity
- Heavy sweating
- Agitation or restlessness
- Rapid heart rate and high blood pressure
- Dilated pupils
- Loss of muscle coordination or twitching muscles
Signs of severe serotonin symptoms include:
- High fever
- Irregular heartbeat
If you are prescribed Cyclobenzaprine or Flexeril, make sure to discuss any current medications you are taking with your doctor and monitor yourself for any symptoms of serotonin syndrome.
- U.S. Food and Drug Administration. (2013). Amrix, Highlights of Prescribing Information.
- Maxwell, Jane. (2015). Trends in the Abuse of Prescription Drugs.
- Elder, N. (1991). Abuse of skeletal muscle relaxants.
- Berman B. D. (2011). Neuroleptic malignant syndrome: a review for neurohospitalists. The Neurohospitalist, 1(1), 41-7.
- U.S. National Library of Medicine. (2018). Rhabdomyolysis.
- U.S. National Library of Medicine, ToxNet. (2016). Cyclobenzaprine.
- Prescribers’ Digital Reference. (n.d.). Cyclobenzaprine hydrochloride – Drug Summary.