The potential side effects of muscle relaxers are related to their action of slowing activity within the nervous system (central nervous system depression). 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 --> - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
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Some individuals experience dizziness after taking a muscle relaxant.
The side effects are usually well-tolerated when used short-term at recommended doses, and include 11 Cashin AG, Folly T, Bagg MK, et al. Efficacy, acceptability, and safety of muscle relaxants for adults with non-specific low back pain: systematic review and meta-analysis. BMJ. 2021;374:n1446. Published 2021 Jul 7. doi:10.1136/bmj.n1446 :
Most people will experience mild to moderate sedation, which can impact daily activities like driving.
Urinary incontinence is a potential side effect of muscle relaxants.
The following table lists the additional side effects associated with certain muscle relaxers.
| Potential Side Effects 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023 | Muscle Relaxer(s) |
|---|---|
| Nervous system side effects | |
| Weakness | Baclofen, tizanidine, orphenadrine |
| Confusion | Baclofen, cyclobenzaprine |
| Over-stimulation | Chlorzoxazone |
| Seizure | Baclofen |
| Tremor | Orphenadrine |
| Psychiatric side effects | |
| Insomnia | Baclofen |
| Nervousness | Cyclobenzaprine, metaxalone |
| Irritability/agitation | Metaxalone, orphenadrine |
| Hallucinations | Orphenadrine |
| Drug abuse or dependence | Carisoprodol, diazepam |
| Gastrointestinal side effects | |
| Diarrhea (severe) | Dantrolene |
| Acid reflux | Cyclobenzaprine |
| Unpleasant taste | Cyclobenzaprine |
| Upset stomach | Metaxalone, orphenadrine |
| Genitourinary side effects | |
| Urine discoloration | Chlorzoxazone |
| Urinary frequency | Baclofen |
| Urinary retention | Baclofen, orphenadrine |
| Urinary tract infection | Tizanidine |
| Other potential side effects | |
| Blurred vision | Cyclobenzaprine, methocarbamol, orphenadrine |
| Increased ocular pressure | Orphenadrine |
| Low blood pressure | Baclofen |
| Increased heart rate | Orphenadrine |
| Increased liver enzymes | Tizanidine |
Muscle relaxers impact each person differently, and while some people may experience more side effects, others may have fewer or no side effects. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
advertisementSerious adverse events are rare, but the presence of certain underlying conditions or the use of concomitant medications increases the risk of these events. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
Drowsiness and sedation can be severe enough to impair the mental and physical abilities of some people, especially older adults or people who take other sedating medications. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
Using muscle relaxers with alcohol or cannabis increases the risk of sedation and impairment. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
Some muscle relaxers cause damage to the liver, and the extent of this damage varies depending on the medication. Liver injury can range from an increase in the levels of liver enzymes to severe liver toxicity and is associated with the following medications 2 Tizanidine. Package Insert. Advagen Pharma Limited; 2020 , 5 Chlorzoxazone. Package Insert. Aurobindo Pharma Limited; 2022 , 9 Dantrolene. Package Insert. Amneal Pharmaceuticals of New York LLC; 2022 :
In most cases, liver function returns to normal when the drug is stopped. 2 Tizanidine. Package Insert. Advagen Pharma Limited; 2020 , 5 Chlorzoxazone. Package Insert. Aurobindo Pharma Limited; 2022 , 9 Dantrolene. Package Insert. Amneal Pharmaceuticals of New York LLC; 2022
Withdrawal effects are possible when abruptly stopping certain muscle relaxers, and these effects are associated with long-term use and/or high doses of the following medications 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 , 7 Soma. Package Insert. Meda Pharmaceuticals Inc; 2023 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023 :
To prevent withdrawal symptoms, these medications are gradually tapered under the supervision of a doctor. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 , 7 Soma. Package Insert. Meda Pharmaceuticals Inc; 2023 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023
advertisementThe following table lists the medical conditions in which certain muscle relaxers have a higher risk of adverse events.
| Medical Condition 2 Tizanidine. Package Insert. Advagen Pharma Limited; 2020 - 4 Cyclobenzaprine. Package Insert. Rising Health, LLC; 2020 , 6 Metaxalone. Package Insert. Amneal Pharmaceuticals LLC; 2022 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023 - 10 | Muscle Relaxers to Avoid |
|---|---|
| Endocrine conditions | |
| Hyperthyroidism | Cyclobenzaprine |
| Cardiovascular conditions | |
| Heart failure | Cyclobenzaprine |
| Abnormal heart rhythm | Cyclobenzaprine |
| Heart block | Cyclobenzaprine |
| Recent heart attack | Cyclobenzaprine |
| Cardiospasm | Orphenadrine |
| Hepatic conditions | |
| Active liver disease (mild to severe) | Dantrolene, tizanidine |
| Severe liver disease | Cyclobenzaprine, dantrolene, diazepam, metaxalone |
| Renal conditions | |
| Impaired kidney function | Metaxalone, methocarbamol (injection) |
| Ocular conditions | |
| Acute narrow-angle glaucoma | Diazepam, orphenadrine |
| Glaucoma (all types) | Orphenadrine |
| Gastrointestinal (GI) conditions | |
| GI obstruction | Orphenadrine |
| Stomach ulcers | Orphenadrine |
| Autoimmune conditions | |
| Myasthenia gravis | Diazepam, orphenadrine |
| Neurologic conditions | |
| Seizure | Methocarbamol (injection) |
| Respiratory conditions | |
| Sleep apnea | Diazepam |
| Respiratory depression | Diazepam |
| Genitourinary conditions | |
| Bladder obstruction | Orphenadrine |
| Enlarged prostate | Orphenadrine |
| Hematologic conditions | |
| Known tendency for anemia | Metaxalone |
Close monitoring for adverse events is advisable if muscle relaxers are used in the conditions listed above. 2 Tizanidine. Package Insert. Advagen Pharma Limited; 2020 - 4 Cyclobenzaprine. Package Insert. Rising Health, LLC; 2020 , 6 Metaxalone. Package Insert. Amneal Pharmaceuticals LLC; 2022 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023 Doctors will gather a detailed medical history before prescribing a muscle relaxer.
The use of muscle relaxers in older adults carries a higher risk for side effects, such as sedation, confusion, urinary retention, or memory problems due to 12 2023 American Geriatrics Society Beers Criteria Update Expert Panel. American Geriatrics Society 2023 updated AGS Beers Criteria for potentially inappropriate medication use in older adults. J Am Geriatr Soc. 2023;71(7):2052-2081. doi:10.1111/jgs.18372 :
It is advisable to discuss these risks with a doctor and consider non-drug therapies, such as massage therapy or strength training, if possible, before prescribing a muscle relaxer for this age group. 12 2023 American Geriatrics Society Beers Criteria Update Expert Panel. American Geriatrics Society 2023 updated AGS Beers Criteria for potentially inappropriate medication use in older adults. J Am Geriatr Soc. 2023;71(7):2052-2081. doi:10.1111/jgs.18372
Muscle relaxers have not been well-researched in pregnant or lactating women, and the effects of these medications on the developing fetus or infant are largely unknown. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
These medications should be used with caution and under the supervision of a doctor in cases of pregnancy or in women who are breastfeeding. Generally, alternative therapies are preferred due to the unknown safety risks of muscle relaxers in these individuals. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
Some muscle relaxers have the potential to be abused because of their calming, sedating, or even euphoric effects. Using the medication for purposes other than the intended use or taking it in excessive amounts can lead to both physical and psychological addiction or dependence. 13 Horsfall JT, Sprague JE. The Pharmacology and Toxicology of the 'Holy Trinity'. Basic Clin Pharmacol Toxicol. 2017;120(2):115-119. doi:10.1111/bcpt.12655
Even when used at regular dose, the body can develop tolerance to certain muscle relaxers and eventually need a higher dose to have the original effect. 7 Soma. Package Insert. Meda Pharmaceuticals Inc; 2023 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023
Muscle relaxers that are commonly associated with the risk of abuse and/or dependence include 7 Soma. Package Insert. Meda Pharmaceuticals Inc; 2023 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023 :
Tolerance to these medications is more likely to develop when used for periods longer than 2-3 weeks. 7 Soma. Package Insert. Meda Pharmaceuticals Inc; 2023 , 8 Diazepam. Package Insert. Mayne Pharma Commercial LLC; 2023
advertisementDue to the significantly increased risk of central nervous system depression, it is strongly advised to avoid combining muscle relaxers with opioid medication such as oxycodone or morphine. Research suggests that there is no improvement in pain relief when combining these medications, and the risks do not outweigh the benefits in most cases. 13 Horsfall JT, Sprague JE. The Pharmacology and Toxicology of the 'Holy Trinity'. Basic Clin Pharmacol Toxicol. 2017;120(2):115-119. doi:10.1111/bcpt.12655
Additionally, benzodiazepines, carisoprodol, and opioids (commonly referred to as the “Holy Trinity”) are avoided within the same prescription due to concerns about safety and the potential for abuse. 13 Horsfall JT, Sprague JE. The Pharmacology and Toxicology of the 'Holy Trinity'. Basic Clin Pharmacol Toxicol. 2017;120(2):115-119. doi:10.1111/bcpt.12655
Muscle relaxers are not recommended for long-term use (more than 3 months). Research suggests that there is little to no improvement when used for long periods, and the risk of side effects or serious adverse events typically outweighs the potential benefit in the long term. 11 Cashin AG, Folly T, Bagg MK, et al. Efficacy, acceptability, and safety of muscle relaxants for adults with non-specific low back pain: systematic review and meta-analysis. BMJ. 2021;374:n1446. Published 2021 Jul 7. doi:10.1136/bmj.n1446
When taking muscle relaxers, it is advisable to report any of the following side effects to a doctor 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023 :
These side effects could be signs of a more serious reaction. 1 Baclofen. Package Insert. Advagen Pharma Limited; 2023 - 10 Methocarbamol. Package Insert. Granules Pharmaceuticals Inc.; 2023
When used as directed, muscle relaxers can provide much-needed relief for several muscle-related conditions. With responsible use and careful monitoring, the benefits of muscle relaxers may be maximized while minimizing potential harm.
Dr. Kathee de Falla is a licensed and certified pharmacist. She has more than a decade of experience providing medical advice and supplying prescription medications in a retail setting. Dr. de Falla spent several years developing drugs at Abbott Laboratories, a pharmaceutical company where she holds a patent for a drug formulation.
