Flexeril (cyclobenzaprine hydrochloride) is a muscle relaxant and pain relief medication. It is often used to manage muscle spasms, sprains, tears, or aches. Flexeril should only be used for up to two or three weeks, as longer use can result in adverse effects. Understanding the potential side effects of Flexeril can help ensure safe use.
- Flexeril (cyclobenzaprine) is a medication commonly used as a muscle relaxant and for pain relief.
- Flexeril should be used for up to two to three weeks. Longer treatments are not recommended and can increase the risk of side effects.
- Flexeril can cause serious side effects and a risk of overdose, particularly if combined with other substances.
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Common or mild side effects of cyclobenzaprine (Flexeril)
Common side effects of Flexeril (cyclobenzaprine) include: [1][2]
- Dizziness
- Confusion
- Weakness
- Fatigue
- Dry mouth
- Constipation
- Increased heart rate
- Pupil dilation
- Acid reflux
- Diarrhea
- Nausea
- Nervousness
Less common side effects that can occur with Flexeril, which are typically mild and do not require intervention, include: [1]
- Blurred vision
- Unpleasant taste
- Headache
- Indigestion and bloating
Serious side effects to watch for
Serious side effects are rare but can occur when using Flexeril alone or alongside additional medications or substances. Serious side effects might also be more likely if high doses are used. Serious side effects of Flexeril can include: [1][2][3]
- Significant changes in heart rate
- Palpitations
- Rash or hives
- Tremors
- Irregular heartbeat
- Heart attack
- Stroke
- Seizures
- Extreme changes in mood and behavior
- Difficulty urinating
- Prolonged constipation
- Hallucinations
- Psychotic symptoms
- Muscle twitches
- Involuntary movements
- Muscle contraction and twisting, leading to abnormal postures
- Delirium
If any of these side effects occur, a professional should be contacted, as it may be necessary to change medication or receive urgent treatment.
Serotonin syndrome: Signs & urgency
Flexeril (cyclobenzaprine) is structurally similar to tricyclic antidepressants and impacts serotonin levels and activity. Because of this, there is a risk of serotonin syndrome when using Flexeril, particularly if it is combined with another serotonergic medication such as antidepressants or certain opioids. [2][3]
Serotonin syndrome can be life-threatening and should be treated urgently to prevent serious harm. Signs of serotonin syndrome can include:
- Nausea, vomiting, diarrhea
- Uncontrollable shaking
- Agitation
- Involuntary muscle movements, twitches, or spasms
- Fever, shivering, sweating
- Severe confusion and disorientation
- Fainting
- Seizures
- Irregular or rapid heart rate
Cyclobenzaprine and mental health considerations
Flexeril use can impact mood, cognition, and behavior. This can include: [1][3][4]
- Psychotic symptoms: Hallucinations, delusions, paranoia
- Mood changes: Low mood, anxiety, nervousness, mania
- Behavioral changes: Agitation, aggression, hyperactivity, talkativeness
- Cognition: Disorientation, confusion, abnormal thoughts, nightmares, or strange dreams
Some people may be more at risk of behavioral and mood changes when taking cyclobenzaprine, such as people with a history of bipolar disorder or other mood disorders. [4]
Precautions
Flexeril should be used with caution in: [1][2]
- People with a history of angle-closure glaucoma
- People with a history of urinary retention
- People with a history of heart issues
- People with impaired liver or kidney functioning
- Pregnant or breastfeeding people
- Children under 15
- Adults over the age of 65
- People with a history of mental health conditions, especially mood disorders or psychosis
Interactions
Flexeril can interact with certain medications and substances, which can impact the effectiveness of the medication or increase the risk of adverse effects. This includes: [1][2]
- Antidepressants and other serotonergic medications can interact with Flexeril, increasing the risk of serotonin syndrome. In particular, monoamine oxidase inhibitors (MAOIs), a type of antidepressant, can have life-threatening effects if used alongside Flexeril. It is recommended to wait 14 days between using MAOIs and Flexeril.
- Central nervous system (CNS) depressant substances, such as opioids, alcohol, or benzodiazepines, can interact with Flexeril, causing increased CNS depressant effects and risk of overdose.
- People taking Tramadol should avoid Flexeril as it may increase the risk of seizures.
Addiction and overdose risks
Flexeril is not considered an addictive substance. However, due to its CNS depressant effects, Flexeril is sometimes misused to enhance the effects of other substances such as opioids or benzodiazepines. As such, it is linked to risks of abuse and addiction, although this risk is considered to be low, so it is not listed as a controlled substance. [5] Flexeril is unlikely to cause physical dependence, although some withdrawal symptoms can occur with abrupt cessation after prolonged use, such as nausea and headaches. [1]
Flexeril overdose
Flexeril overdose is unlikely to be fatal, although a combination of Flexeril and other substances, particularly in large doses, can cause life-threatening effects. Flexeril overdose causes symptoms such as: [1][2]
- Extreme sedation
- Changes in heart rate
- Shaking
- Confusion
- Nausea
Because Flexeril causes CNS depressant effects, using it with other CNS depressant substances, such as opioids, can lead to dangerous or life-threatening overdose symptoms such as: [1]
- Chest pain
- Heart attack
- Severe change in blood pressure
- Seizures
Managing and minimizing side effects
Side effects are more likely to occur and be more severe if large doses are used. As such, using the lowest effective dose possible can help reduce the risk of side effects. Similarly, serious effects may be more likely to occur with prolonged use, so it is advised to use Flexeril for the shortest possible time to manage symptoms.
Misusing or abusing Flexeril, including using large or frequent doses, using it for a prolonged period, or using it alongside illicit substances, can increase the risk of side effects and overdose and should be avoided.
Some side effects require medical advice and intervention, as they could be dangerous or life-threatening. Mild side effects tend not to require professional intervention and could be managed with lifestyle or dietary changes.
- Ensuring adequate hydration can help reduce the severity of some side effects, particularly gastrointestinal issues, headaches, and fatigue. Similarly, consuming a healthy and balanced diet can also help manage these symptoms.
- Flexeril can cause drowsiness, dizziness, and fatigue. If so, it may be helpful to take the medication in the evening to prevent daytime tiredness. It is also advisable not to drive or operate heavy machinery if it impacts alertness and ability to concentrate. [1]
- Sometimes, medications such as antinausea medications, non-opioid pain relief, or antacids can help with the side effects of Flexeril. However, it is important to discuss this with the prescribing doctor first, to ensure safe use.
When to contact your medical provider
Cyclobenzaprine is typically prescribed for only two or three weeks to manage acute symptoms. During this time, people may need to contact their medical provider immediately if they notice any serious side effects to review treatment and provide appropriate care.
People who are misusing or abusing Flexeril, such as taking it when not prescribed, using large doses, or administering it in an unintended manner, may benefit from professional support in reducing and stopping use. Medical professionals can help make appropriate referrals to substance use specialists if required.
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