Methocarbamol is a prescription muscle relaxant used to treat muscle pain and spasms related to musculoskeletal conditions. Methocarbamol can be safe and effective when used as prescribed. However, it can interact with other medications and substances, which may lead to dangerous effects.
- Methocarbamol, a muscle relaxant, has depressant effects on the central nervous system.
- If methocarbamol is combined with other central nervous system depressants, dangerous effects can occur, including extreme sedation and respiratory depression.
- Some medications are safe to use alongside methocarbamol. Always check with the prescribing doctor before commencing a new medication to find out if it is safe.
How methocarbamol works and why drug interactions occur
Methocarbamol is a skeletal muscle relaxant used to treat acute painful musculoskeletal conditions. Its exact mechanism of action is not fully understood, although it is known to act as a central nervous system (CNS) depressant. [1] In typically prescribed doses, methocarbamol does not cause high levels of sedation. However, it is known to enhance the sedating effects of alcohol or other CNS depressants. [2]
Similarly, methocarbamol is known to enhance or increase analgesic effects when combined with pain-relieving medications, thus indicating an interaction with these types of medications. [2]
Because of its effects, methocarbamol interacts with other CNS depressants to create increased depressant effects. This can lead to dangerous effects, including extreme sedation and impaired breathing. [1] As such, using potent CNS depressant medications alongside methocarbamol is typically not recommended and can result in dangerous effects. If a combination of analgesic medications is prescribed, it may be necessary to reduce the dosages to prevent adverse outcomes.
Major methocarbamol drug interactions
Methocarbamol can interact with various drugs, most commonly those that also cause CNS depressant effects, which can result in dangerous effects. Alcohol, opioids, and benzodiazepines are examples of other CNS depressants that are dangerous to combine with methocarbamol. Other drug interactions with methocarbamol can include anticholinergic medications and medications that lower seizure threshold.
CNS depressants
Methocarbamol can have dangerous interactions when combined with CNS depressants, such as: [1][3][4][5]
- Alcohol: Combining alcohol with methocarbamol can be particularly dangerous, as this can impair cognitive and motor function, thus causing an increased risk of accidental harm. It can also increase the risk of CNS depressant effects, including severe sedation and breathing issues, and an increased risk of overdose.
- Other muscle relaxants: Using methocarbamol alongside other muscle relaxants can increase the risk of CNS depressant effects.
- Opioid medications and illicit opioids: Prescribed opioids, such as hydrocodone and codeine, as well as illicit opioids, such as heroin or street fentanyl, can cause severe CNS depressant effects when combined with methocarbamol, which can lead to overdose and fatality.
- Benzodiazepines, sleep medications, and barbiturates: These medications cause sedating effects, which can be significantly increased when combined with methocarbamol. This can cause significant impairments in functioning and a high risk of CNS depressant effects, such as respiratory depression.
Anticholinergic medications
Methocarbamol can interact with anticholinergic medications, such as: [6][7]
- Antihistamines, such as diphenhydramine
- Parkinson’s medications, such as benztropine
- Antipsychotics and tricyclic antidepressants
Methocarbamol can enhance the anticholinergic effects of these medications, which can increase the risk of side effects, especially in older adults. [6]
Medications that can lower seizure threshold
As a CNS depressant, methocarbamol can lower the seizure threshold. When combined with other medications that lower seizure threshold, the risk of seizures can be significantly increased. This can include medications such as: [8]
- Antihistamines, such as diphenhydramine
- Other muscle relaxants
- Some antidepressants, including bupropion and amitriptyline
- Some antipsychotics, such as clozapine and chlorpromazineÂ
- Stimulants, such as medications for attention-deficit/hyperactivity disorder (ADHD)
Methocarbamol and polysubstance use
Methocarbamol is considered non-addictive and is not typically abused for recreational reasons, except in combination with alcohol or other drugs. Methocarbamol and polysubstance use can result in dangerous effects. In particular, this can increase the risk of abuse and addiction, due to the enhanced sedation or ‘high’. This can occur when methocarbamol is used with prescribed medications or with illicit substances. [6]
Similarly, polysubstance use can increase the risk of unpleasant or dangerous side effects and drug interactions. These effects can result in dangerous or fatal outcomes and can increase the risk of accidental injury and harm due to increased drowsiness and impaired coordination.Â
This may be particularly risky for older adults, as this age group may be more likely to experience impaired coordination and cognitive function and a higher risk of falls.Â
People with a history of substance abuse and addiction can also experience an increase in these risks and may be advised to use methocarbamol with caution, reduced doses, or not at all. [6]
Signs of dangerous drug interactions
Medications, alcohol, or illicit substances that interact with methocarbamol can cause dangerous effects, which may require medical intervention. Signs of dangerous interactions that should be reported to a physician immediately include: [3][4][6]
- Severe sedation
- Difficulty breathing and chest pain
- Blue lips or fingers
- Respiratory depression
- Severely impaired coordination or cognitive ability
- Extreme dizzinessÂ
- Loss of consciousness
- SeizuresÂ
What to do during an emergency
If a dangerous drug interaction is suspected or signs of overdose are observed, call 911 immediately, as urgent medical care may be required, particularly if the individual has stopped breathing, lost consciousness, or is experiencing seizures.
If possible, try to gather information about the individual, their prescription medications, and what, if any, other substances have been used alongside methocarbamol. This can help inform treatment.
Prevention and safe medication use
Some medications can be safely used alongside methocarbamol. The prescribing physician can assess each individual and their treatment needs, and determine which medications are safe and appropriate. For example, methocarbamol may be used alongside certain pain medications to enhance analgesic effects. [6]
To use methocarbamol safely, always:
- Inform the prescribing doctor of any other medications or illicit substances that are being used, as this can impact methocarbamol doses and safe use.
- Inform the doctor of any physical health conditions, including liver or kidney issues, as these may impact the safety of methocarbamol use.
- Take methocarbamol exactly as prescribed, at the correct time and in the correct dose. Never take more than prescribed or take a double dose to make up for a missed dose.
- Stop methocarbamol treatment when advised to by the prescribing doctor, using reduced doses if recommended.
- Avoid alcohol and illicit substances while taking methocarbamol.
- Avoid commencing new medications while taking methocarbamol unless expressly advised to by a licensed physician.
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