Can someone faint from taking muscle relaxers, such as cyclobenzaprine?

From the Guidelines

Yes, someone can faint from taking muscle relaxers like cyclobenzaprine, as they can cause dizziness, drowsiness, and a drop in blood pressure, which may lead to fainting, especially when standing up quickly. Cyclobenzaprine (commonly sold as Flexeril) is a skeletal muscle relaxant that can affect the central nervous system, leading to adverse events such as dizziness and drowsiness, as reported in a systematic review of skeletal muscle relaxants for acute and chronic low back pain 1. The review found that skeletal muscle relaxants, including cyclobenzaprine, were associated with a higher total number of adverse events (RR, 1.50 [CI, 1.14 to 1.98]) and central nervous system adverse events (RR, 2.04 [CI, 1.23 to 3.37]) compared with placebo.

Some key points to consider when taking cyclobenzaprine include:

• Taking the medication as directed, typically in 5-10 mg tablets up to three times daily, with a maximum recommended dose of 30 mg per day
• Being aware of the potential for dizziness and drowsiness, and taking steps to mitigate these effects, such as sitting or lying down immediately if lightheadedness or dizziness occurs
• Avoiding sudden position changes, staying hydrated, and not combining the medication with alcohol or other central nervous system depressants
• Contacting a healthcare provider promptly if fainting occurs while taking the medication, as dosage adjustment or medication change may be necessary.

It's also important to note that the evidence for the efficacy and safety of cyclobenzaprine for low back pain is limited, with only one lower-quality trial evaluating its use for chronic low back pain 1. However, the potential risks associated with cyclobenzaprine, including the risk of fainting, highlight the need for careful consideration and monitoring when prescribing this medication.

From the FDA Drug Label

The FDA drug label does not answer the question.

From the Research

Muscle Relaxers and Fainting

• Fainting, also known as syncope, is a sudden loss of consciousness caused by a lack of blood flow to the brain.
• While the provided studies do not directly address fainting as a side effect of muscle relaxers like cyclobenzaprine, they do mention drowsiness, sedation, and dizziness as common adverse effects 2, 3, 4, 5, 6.
• These side effects could potentially increase the risk of fainting, especially if the individual is prone to dizziness or lightheadedness when standing up or changing positions.
• Cyclobenzaprine, in particular, has been shown to cause sedative effects via off-target antagonism of central histamine H1 receptors, which could contribute to an increased risk of fainting 4.

Adverse Effects of Muscle Relaxers

• The studies highlight the importance of considering the potential adverse effects of muscle relaxers, including:
  • Drowsiness and sedation 2, 3, 4
  • Dizziness and lightheadedness 3, 5, 6
  • Dry mouth 2, 6
  • Anticholinergic side effects (e.g., blurred vision, constipation) 5
• These adverse effects can vary depending on the specific muscle relaxer used, with some agents like metaxalone having fewer reported side effects 5.
• Carisoprodol, on the other hand, has been associated with a higher risk of physical and psychological dependence, as well as toxicity 5.

Efficacy and Safety of Muscle Relaxers

• The studies demonstrate the efficacy of various muscle relaxers, including cyclobenzaprine, metaxalone, and carisoprodol, in treating muscle spasm and musculoskeletal conditions 2, 5, 6.
• However, the safety profiles of these agents differ, with some having a higher risk of adverse effects or toxicity 5, 6.
• Cyclobenzaprine, in particular, has been shown to be effective in reducing muscle spasm and pain, but its use is associated with a higher risk of sedation and drowsiness 2, 4.