Do Muscle Relaxers Affect Oxygen Levels? A Guide to Respiratory Risks

October 10, 2025 •

4 min read

A 2018 study in The Lancet Respiratory Medicine found that neuromuscular blockers used during general anesthesia were associated with a significantly increased risk of respiratory complications after surgery. This raises the important question: Do muscle relaxers affect oxygen levels in broader, non-surgical contexts, and what precautions should patients be aware of?

Quick Summary

Muscle relaxers can cause respiratory depression, potentially affecting oxygen levels by slowing breathing, especially in high doses or when combined with other central nervous system depressants. This risk is heightened for patients with pre-existing respiratory conditions like COPD or sleep apnea.

Key Points

CNS Depression is the Key Cause: Most muscle relaxers slow down brain activity, which can suppress the respiratory control centers in the brainstem.
Risk Amplified by Other Depressants: Combining muscle relaxers with alcohol, opioids, or benzodiazepines significantly increases the risk of dangerous respiratory depression.
Vulnerability for Respiratory Conditions: Patients with pre-existing respiratory diseases like COPD, asthma, or sleep apnea are at a higher risk of breathing problems from muscle relaxers.
Dosage Matters: The higher the dose of a muscle relaxer, the greater the potential for a dose-dependent respiratory depression side effect.
Look for Overdose Signs: Severe drowsiness, slow or shallow breathing, and confusion are all signs of a potential overdose and require immediate medical attention.
Not Just Brain Effects: Certain muscle relaxers, like baclofen and carisoprodol, can directly weaken the muscles involved in breathing, worsening respiratory function.
Postoperative Concerns: Neuromuscular blockers used during surgery are linked to an increased risk of respiratory complications, including low oxygen levels, after the procedure.

The Pharmacological Mechanism Behind Respiratory Effects

The primary reason that muscle relaxers can impact oxygen levels is their effect on the central nervous system (CNS). Most common muscle relaxers, such as cyclobenzaprine and baclofen, are centrally acting agents, meaning they work by depressing CNS activity. They increase the activity of gamma-aminobutyric acid (GABA), a neurotransmitter that slows down brain function. In doing so, these medications can inadvertently suppress the respiratory control centers located in the brain's medulla oblongata, which regulate the rate and depth of breathing.

When these control centers are sufficiently depressed, breathing becomes slower and shallower, a condition known as respiratory depression. This can lead to a decrease in the amount of oxygen taken into the lungs, resulting in lower oxygen levels in the blood. This effect is dose-dependent, meaning a higher dose increases the risk and severity of respiratory depression.

Weakening of Respiratory Muscles

In addition to the central effect on the brain, some muscle relaxers, such as baclofen and carisoprodol, can also have a peripheral effect by weakening the skeletal muscles, including the diaphragm and intercostal muscles that assist with breathing. For patients with underlying respiratory issues, this muscular weakening can further compromise their ability to breathe effectively, contributing to dangerously low oxygen saturation.

How Different Types of Muscle Relaxers Impact Respiration

The effect on oxygen levels can vary depending on the specific type of muscle relaxant, its dosage, and the presence of other medications.

Centrally-Acting Skeletal Muscle Relaxants

This class of drugs includes many commonly prescribed medications like cyclobenzaprine (Flexeril) and methocarbamol (Robaxin). Research has indicated a link between the use of these muscle relaxants and an increased risk of chronic obstructive pulmonary disease (COPD) exacerbations. In cases of overdose, particularly when combined with other CNS depressants, these medications can lead to profound respiratory depression.

Neuromuscular Blocking Agents (NMBAs)

NMBAs are a different type of muscle relaxant used primarily in surgical settings to induce temporary paralysis. These drugs act at the neuromuscular junction, blocking nerve impulses to skeletal muscles. Postoperative studies have shown a connection between the use of NMBAs during surgery and a higher incidence of respiratory complications, including decreased oxygen saturation and re-intubation. The risk is particularly elevated in shorter operations and in patients with residual neuromuscular block after the procedure.

Factors That Increase the Risk of Low Oxygen Levels

Several factors can increase the likelihood of experiencing respiratory problems while taking muscle relaxers:

Combination with other CNS depressants: This is one of the most dangerous risk factors. Combining muscle relaxers with substances like alcohol, opioids, or benzodiazepines can significantly amplify their sedative effects and the risk of respiratory arrest.
Pre-existing respiratory conditions: Individuals with conditions such as Chronic Obstructive Pulmonary Disease (COPD), asthma, or sleep apnea are particularly vulnerable. Muscle relaxers can worsen symptoms and increase the risk of exacerbations or airway obstruction.
High dosage: The risk of respiratory depression increases with higher doses of muscle relaxers. An overdose can be fatal.
Age: Elderly individuals are more sensitive to the CNS-depressant effects of these drugs, increasing their risk of side effects like drowsiness, impaired coordination, and falls.

Comparison of Common Muscle Relaxers and Their Respiratory Impact


Muscle Relaxer	Primary Mechanism	Respiratory Risk	Special Considerations
Cyclobenzaprine (Flexeril)	Centrally-acting CNS depressant	Moderate; increased risk of respiratory depression with high doses or other depressants. Linked to increased COPD exacerbation risk.	Also has anticholinergic effects, which can cause other side effects.
Baclofen	Centrally-acting CNS depressant that also weakens respiratory muscles.	Moderate to High; overdose can cause severe respiratory depression.	Must be tapered off gradually to avoid withdrawal symptoms.
Methocarbamol (Robaxin)	Centrally-acting CNS depressant.	Moderate; generally considered less sedating, but still poses a risk, particularly in high doses. Linked to increased COPD exacerbation risk.	Less expensive and potentially less sedating than other options.
Carisoprodol (Soma)	Centrally-acting CNS depressant; also has muscle-weakening effects.	High; significant abuse potential and risk for severe respiratory depression, especially when combined with other CNS depressants.	Can be habit-forming; often used for short-term relief only.
Tizanidine	Centrally-acting alpha-2 adrenergic agonist.	Moderate; can cause sedation and respiratory depression, particularly with other sedatives.	Can cause significant drowsiness and dry mouth.

Recognizing the Signs of Respiratory Distress

Monitoring for signs of respiratory distress is crucial when taking muscle relaxers. You should seek immediate medical attention if you or someone else exhibits any of the following symptoms:

Slow or shallow breathing
Shortness of breath or difficulty breathing
Feeling faint, dizzy, or unusually tired
Confusion or difficulty speaking clearly
Blue or purple-colored lips or fingernails
Extreme drowsiness or inability to stay awake
Chest tightness or pain

Conclusion: Using Muscle Relaxers Safely

Muscle relaxers can be effective for managing pain and spasms, but the potential to affect oxygen levels through respiratory depression must be taken seriously. The risk is elevated by higher doses, mixing with other CNS depressants, and having pre-existing respiratory conditions like COPD or sleep apnea. To ensure safe use, it is critical to follow your doctor's exact instructions, avoid alcohol and other sedatives, and be aware of the signs of respiratory distress. For most conditions, muscle relaxers are intended for short-term use, and prolonged use should be managed carefully with a healthcare provider. Always discuss any concerns or changes to your medication regimen with a healthcare professional.

For more information on the appropriate use of muscle relaxants for back pain, you can visit Spine-health.

Frequently Asked Questions

Yes, in rare and severe cases, a muscle relaxer can cause a person to stop breathing, particularly in an overdose situation or when combined with other CNS depressants like alcohol or opioids. This is a medical emergency requiring immediate attention.

Centrally-acting muscle relaxers like Flexeril work by depressing the central nervous system, while neuromuscular blocking agents (NMBAs) used in surgery directly block nerve impulses to muscles. Both can cause respiratory depression, but through different mechanisms. Centrally-acting types pose a risk in overdose or with drug interactions, while NMBAs carry a risk of post-operative complications if their effects are not fully reversed.

While all muscle relaxers carry some risk of respiratory depression, some are considered less sedating. For instance, methocarbamol is generally seen as less sedating than others, but it is not without risk, especially for individuals with conditions like COPD.

You should monitor for signs of respiratory depression, including slow or shallow breathing, unusual fatigue, confusion, or blue-tinged lips or nails. A pulse oximeter can measure oxygen saturation, but clinical signs are often more telling outside of a hospital setting.

Muscle relaxers can worsen sleep apnea symptoms by relaxing the throat muscles and increasing the risk of airway obstruction. If you have sleep apnea, it's crucial to discuss this risk with your doctor and proceed with extreme caution.

Call for emergency medical help immediately. If possible, provide information about the medication they took and any others, including alcohol, to the emergency responders. Do not try to make them vomit or give them anything to eat or drink.

Most over-the-counter pain relievers are not muscle relaxers. However, some antihistamines with sedating properties can depress the CNS and affect breathing, and they should not be mixed with prescription muscle relaxers.