Can a muscle relaxer cause diarrhea?: Understanding the GI Risks and How to Cope

October 10, 2025 •

4 min read

According to data from clinical trials and postmarketing reports, digestive issues like diarrhea are a potential side effect of certain muscle relaxants, though often less common than drowsiness or dry mouth. This guide explores the question, "Can a muscle relaxer cause diarrhea?", and provides insight into the specific medications involved and potential management strategies.

Quick Summary

Certain muscle relaxants, including cyclobenzaprine and dantrolene, can cause diarrhea, though this is often a less frequent side effect than constipation. The risk varies by medication and individual patient response, and medical consultation is essential for managing persistent symptoms.

Key Points

Yes, it's possible: Diarrhea can be a side effect of some muscle relaxants, though often less common than constipation.
Specific culprits: Cyclobenzaprine (Flexeril) and Dantrolene are particularly noted for their association with diarrhea, with Dantrolene posing a risk of severe diarrhea.
Multiple mechanisms: The cause can be a simple disruption of gut motility or, rarely, a symptom of serotonin syndrome.
Seek medical advice: For persistent or severe symptoms, consulting a healthcare provider is crucial to determine the cause and adjust treatment.
Hydration is key: Managing mild diarrhea involves staying hydrated and potentially following a bland diet.
Not all are equal: The frequency and severity of gastrointestinal side effects, including diarrhea, can vary significantly between different muscle relaxers.

The Link Between Muscle Relaxers and Diarrhea

While many people associate muscle relaxants with constipation due to their anticholinergic properties that slow intestinal movement, diarrhea is also a possible adverse effect. The gastrointestinal system is a delicate balance, and any medication that alters nerve signals or muscle function can disrupt this balance. For some individuals, this disruption can manifest as diarrhea, with different medications carrying varying levels of risk.

It is important to remember that individual responses to medication differ significantly. What causes diarrhea in one person might cause constipation or no gastrointestinal side effects at all in another. Factors such as dosage, duration of use, and a person's underlying health can all play a role in how a muscle relaxer affects their digestive system.

Specific Muscle Relaxers and Their Gastrointestinal Effects

Not all muscle relaxers have the same side-effect profile. Here is a look at some common medications and their relationship with gastrointestinal issues, specifically diarrhea.

Cyclobenzaprine (Flexeril): This is one of the most frequently cited muscle relaxants associated with diarrhea. Clinical studies and postmarketing reports indicate that diarrhea is a reported side effect, though it is often mentioned alongside other common GI issues like nausea and constipation. In some cases, it can also be a symptom of the more serious, though rare, serotonin syndrome, particularly when taken with other serotonergic drugs.
Dantrolene: This muscle relaxer is particularly noted for potentially causing severe diarrhea. Given the seriousness of this side effect, it's crucial for patients taking dantrolene to be aware of the risk and report any persistent or severe diarrhea to their healthcare provider immediately.
Carisoprodol (Soma): This medication can cause general gastrointestinal disturbances, and diarrhea is listed as a possible side effect, though the exact mechanism is not fully understood.
Methocarbamol (Robaxin): Gastrointestinal upset, nausea, and vomiting are common side effects of methocarbamol. While diarrhea is less frequently listed in clinical summaries compared to other GI issues, it can occur in some individuals.
Tizanidine (Zanaflex): Common gastrointestinal side effects for tizanidine include dry mouth, constipation, and vomiting. Diarrhea is less commonly reported but remains a possibility.

Why Muscle Relaxers May Cause Diarrhea

The mechanisms behind why a muscle relaxer can cause diarrhea are varied and can involve multiple systems within the body. While some actions are well-understood, others are less clear and depend on the specific drug.

Disruption of Gut Motility: Many muscle relaxants work by affecting the central nervous system to reduce muscle spasms. This can inadvertently disrupt the normal peristaltic movements of the intestines. In some cases, this disruption slows down the gut, causing constipation. In other cases, it can lead to inconsistent or erratic movements that result in diarrhea.
Serotonin Syndrome: For certain muscle relaxers like cyclobenzaprine, there is a risk of developing serotonin syndrome, especially when combined with other serotonergic medications such as antidepressants. This syndrome is caused by excessive serotonin levels and can lead to a cascade of symptoms, including severe diarrhea, agitation, and a rapid heart rate. This is a serious condition that requires immediate medical attention.
Individual Sensitivity: Like with any medication, some people may simply be more sensitive to a drug's effects. Genetic factors, pre-existing gastrointestinal conditions, and a person's overall gut microbiome can influence how their body reacts to a muscle relaxer.
Excipient-related issues: In rare cases, the non-active ingredients (excipients) in a medication might contribute to gastrointestinal distress. However, this is far less likely than the pharmacological effects of the active drug itself.

Managing Diarrhea Caused by Muscle Relaxers

If you experience diarrhea while taking a muscle relaxer, it's important to approach the situation carefully and in consultation with your healthcare provider. Here are some general guidelines for management:

Do not stop taking your medication abruptly: Never stop a prescription medication without consulting your doctor first. For some drugs, like tizanidine, sudden cessation can cause withdrawal symptoms, including rebound hypertension and increased muscle tone.
Contact your healthcare provider: Discuss your symptoms with your doctor, especially if the diarrhea is persistent, severe, or accompanied by other concerning symptoms. They can help determine if the medication is the cause and decide on the best course of action.
Stay hydrated: Diarrhea can quickly lead to dehydration. Increase your intake of fluids, including water, broths, and electrolyte-rich beverages, to replace lost fluids and minerals.
Adjust your diet: For mild symptoms, switching to a bland diet (BRAT—bananas, rice, applesauce, toast) can help firm up your stools. Avoid spicy, fatty, or high-fiber foods that can irritate the digestive system.
Dosage or medication change: In some cases, a healthcare provider may adjust your dosage or suggest switching to a different muscle relaxer with a more favorable side-effect profile for you.

Comparison of Muscle Relaxers and Potential GI Side Effects


Potential Side Effect	Cyclobenzaprine (Flexeril)	Dantrolene	Methocarbamol (Robaxin)	Tizanidine (Zanaflex)
Diarrhea	Possible (1-3% of patients)	Severe diarrhea possible	Less common, GI upset reported	Less common
Constipation	Common (1-3% of patients)	Possible	Common	Common
Nausea/Upset Stomach	Common (1-3% of patients)	Possible	Common	Common

Conclusion

In conclusion, the question, "Can a muscle relaxer cause diarrhea?", has a clear answer: yes. While it may not be the most common gastrointestinal side effect, it is a documented risk, especially with medications like cyclobenzaprine and dantrolene. The likelihood and severity of diarrhea depend on the specific medication, dosage, and individual patient factors. Patients should monitor for any changes in bowel habits and communicate them with their healthcare provider. By working with a doctor, patients can find an effective treatment plan for their muscle spasms while minimizing uncomfortable side effects. Staying hydrated and making dietary changes can help manage mild symptoms, but professional medical guidance is essential for persistent or severe issues.

Disclaimer: The information provided here is for informational purposes only and does not constitute medical advice. Always consult your healthcare provider for diagnosis and treatment.

For more in-depth information about drug side effects, consult MedlinePlus, a service of the U.S. National Library of Medicine.(https://medlineplus.gov/)

Frequently Asked Questions

No, diarrhea is generally a less common side effect than issues like drowsiness, dry mouth, or constipation. However, it is a documented risk for several specific medications, such as cyclobenzaprine.

Yes, clinical studies and postmarketing reports list diarrhea as a possible side effect of cyclobenzaprine, occurring in 1% to 3% of patients.

You should contact your healthcare provider to discuss your symptoms. They can assess if the medication is the cause and recommend a treatment plan, which may include managing symptoms or switching to an alternative medication.

While usually a minor side effect, severe diarrhea, especially when accompanied by other symptoms like agitation, fast heartbeat, or hallucinations, could indicate a rare but serious condition called serotonin syndrome. Seek immediate medical attention if these symptoms occur.

Methocarbamol can cause gastrointestinal upset, but diarrhea is not listed as frequently as other side effects like nausea and vomiting. Some individual variation can occur.

Yes, the risk of diarrhea varies. For instance, Dantrolene is specifically noted for potentially causing severe diarrhea, while other medications like Tizanidine have different primary gastrointestinal side effects.

Many muscle relaxers are intended for short-term use. While side effects can occur at any point, it is important to monitor for any side effects throughout the treatment period.

For mild cases, focusing on hydration is essential to replace lost fluids. Eating a bland diet, such as the BRAT diet, can also help firm up stools.