From the Guidelines
Yes, muscle relaxants can cause weakness as a side effect, as they work by depressing the central nervous system or directly affecting muscle fibers, leading to generalized muscle weakness beyond the targeted area. This is supported by studies such as 1, which found that skeletal muscle relaxants were associated with a higher total number of adverse events, including central nervous system adverse events, compared to placebo. The weakness typically occurs because these medications don't selectively target only painful or spasming muscles but affect the entire muscular system to some degree.
Some key points to consider when prescribing muscle relaxants include:
- The weakness is usually dose-dependent, with higher doses causing more pronounced effects 1
- Elderly patients and those with certain medical conditions may experience more significant weakness 1
- Other common side effects include drowsiness, dizziness, and dry mouth, which can compound the feeling of weakness 1
- The side effect is usually temporary and resolves when the medication is discontinued or the dose is reduced
It's essential to weigh the potential benefits and harms of muscle relaxants before starting therapy, especially in patients with a history of substance abuse or those who are vulnerable to addiction 1. If you experience concerning weakness while taking muscle relaxants, contact your healthcare provider, as dosage adjustment may be necessary.
From the FDA Drug Label
Cyclobenzaprine HCl relieves skeletal muscle spasm of local origin without interfering with muscle function. The FDA drug label does not answer the question.
From the Research
Muscle Relaxants and Muscle Weakness
- Muscle relaxants can cause muscle weakness as a side effect, as reported in a study on the toxic effects of muscle relaxants 2.
- The study found that persistent muscle weakness can occur after long-term administration of non-depolarizing muscle relaxants 2.
- Another study compared the efficacy and safety of different skeletal muscle relaxants and found that baclofen is associated with more weakness compared to tizanidine 3.
- A review of three commonly prescribed skeletal muscle relaxants found that carisoprodol, cyclobenzaprine, and metaxalone have varying side effects, but muscle weakness is not specifically mentioned as a common side effect of these medications 4.
- A double-blind comparative trial of tizanidine and baclofen found that muscle weakness was a more frequent side-effect of baclofen compared to tizanidine 5.
Side Effects of Muscle Relaxants
- Muscle relaxants can cause a range of side effects, including ataxia, sedation, and impairment of voluntary motor functions 6.
- The side effects of muscle relaxants can vary depending on the specific medication and the individual patient 3.
- Some muscle relaxants, such as carisoprodol, have a higher potential for physical and psychological dependence and toxicity compared to others 4.
- Tizanidine and baclofen have been found to have similar efficacy in treating spasticity, but with different side effect profiles 5.