Can Mestinon cause diarrhea? Understanding the Side Effect and Its Management

October 9, 2025 •

4 min read

According to prescribing information, gastrointestinal symptoms like diarrhea, nausea, and abdominal cramps are among the most common side effects reported by people taking Mestinon (pyridostigmine). While these side effects can be bothersome, they often resolve over time as your body adjusts to the medication.

Quick Summary

Mestinon, or pyridostigmine, is a common anticholinesterase inhibitor that can trigger diarrhea and other gastrointestinal distress by increasing intestinal muscle activity. Mild symptoms often subside with time or dosage adjustments. However, severe diarrhea combined with other symptoms can signal a potentially serious overdose known as cholinergic crisis. Management options range from simple dietary changes to medication adjustments under a doctor's care.

Key Points

Yes, Mestinon can cause diarrhea: Diarrhea is a common muscarinic side effect of Mestinon (pyridostigmine bromide), occurring because the drug increases acetylcholine, which stimulates intestinal motility.
Symptom severity varies: Mild diarrhea often occurs when first starting the medication or with minor dosage adjustments, and may resolve as the body adapts.
Overdose can cause severe diarrhea: Severe diarrhea combined with significant muscle weakness can indicate a potentially life-threatening overdose known as cholinergic crisis.
Management includes adjustments and diet: Strategies to manage diarrhea include taking the medication with food, adjusting the dosage under a doctor's supervision, staying hydrated, and avoiding irritating foods.
Consult your doctor before using OTC anti-diarrheals: Medications like loperamide should only be used after consulting a healthcare provider, as they can mask signs of an overdose.
Work with your healthcare provider: Ongoing, bothersome side effects warrant a discussion with your doctor, who may adjust your dosage or prescribe an additional medication to help.

The Link Between Mestinon and Diarrhea

Yes, Mestinon, the brand name for the active ingredient pyridostigmine bromide, can cause diarrhea. This gastrointestinal side effect is directly related to the drug's mechanism of action as a cholinesterase inhibitor.

To understand why this happens, it's helpful to know how the medication works. Mestinon is primarily used to treat myasthenia gravis, a neuromuscular disease that causes muscle weakness. In patients with this condition, the body's immune system attacks and blocks the receptors for a neurotransmitter called acetylcholine. By inhibiting the enzyme that breaks down acetylcholine, Mestinon effectively increases its concentration at the neuromuscular junction, improving muscle strength.

The issue arises because acetylcholine also plays a crucial role in the body's involuntary functions, including stimulating the digestive system. When Mestinon increases acetylcholine levels, it also ramps up the wave-like muscle contractions (peristalsis) in the intestines. This increased intestinal motility can lead to cramping, abdominal discomfort, and ultimately, diarrhea.

Other common muscarinic side effects

Diarrhea is one of several so-called "muscarinic" side effects of Mestinon, which are related to its impact on the parasympathetic nervous system. Other common symptoms can include:

Nausea and vomiting
Abdominal cramps
Increased salivation
Increased sweating
Increased bronchial secretions
Pupil constriction (miosis)

How to Manage Diarrhea Caused by Mestinon

Managing diarrhea from Mestinon involves a combination of strategies, with the most important step being communication with your doctor. Never stop or change your dosage without consulting a healthcare professional, as abrupt cessation can lead to life-threatening muscle weakness.

Doctor-supervised adjustments

Dose titration: Often, side effects are most prominent when starting the medication. Your doctor may start you on a low dose and increase it gradually to allow your body to adjust.
Dosage timing: Altering the timing of your doses, as directed by your doctor, can sometimes help manage symptoms.
Prescription medication: For persistent and bothersome gastrointestinal side effects, some physicians may prescribe an anticholinergic agent like propantheline (Pro-Banthine) to be taken alongside Mestinon. This can help reduce gastrointestinal spasms.

Dietary and lifestyle changes

Take with food: Taking Mestinon with food can help reduce gastrointestinal upset. Some anecdotal reports suggest that high-fat foods, like whole milk, can be particularly helpful.
Stay hydrated: Diarrhea can lead to dehydration. Ensure you are drinking plenty of fluids, such as water, juice, and broth, to replace lost electrolytes.
Eat smaller, frequent meals: This can be easier on your digestive system than large meals.
Avoid irritants: Limit foods and drinks that can make diarrhea worse, such as caffeine, alcohol, very spicy or fatty foods, and excessive fiber.
Try the BRAT diet: For a short period, eating a bland diet consisting of Bananas, Rice, Applesauce, and Toast can help ease digestive upset.

Over-the-counter (OTC) medications

Loperamide (Imodium): This is a safe OTC medication for controlling diarrhea, but it should only be used under the guidance of your neurologist, as it could mask signs of overdose.
Bismuth subsalicylate (Pepto Bismol): This can also help with symptom relief, but again, consult your doctor before using.

Cholinergic Crisis: When Diarrhea Becomes a Warning Sign

While mild diarrhea is a common and manageable side effect, severe diarrhea can be a symptom of a potentially life-threatening overdose called cholinergic crisis. This condition is characterized by an overstimulation of the nervous system due to too much Mestinon. It's critical to understand the distinction between regular side effects and this medical emergency.

Distinguishing Cholinergic Crisis from Myasthenic Crisis

It can be challenging for both patients and doctors to differentiate between a cholinergic crisis (overdose) and a myasthenic crisis (underdose), as both can cause severe muscle weakness. However, the accompanying symptoms can offer a critical clue.


Symptom	Common Mestinon Side Effect	Cholinergic Crisis (Overdose)	Myasthenic Crisis (Underdose)
Diarrhea	Mild to moderate, especially when starting medication.	Severe, frequent, and urgent.	Generally absent, or may have slowed bowel movements.
Muscle Weakness	Mild muscle cramping or twitching.	Worsening, severe weakness. Can affect breathing.	Worsening, severe weakness. Can affect breathing.
Salivation & Mucus	Increased saliva.	Excessive salivation and bronchial secretions.	Normal or decreased.
Pupils	Pinpoint pupils (miosis).	Pinpoint pupils.	Normal or dilated.
Heart Rate	Normal or slowed slightly.	Slow heart rate (bradycardia).	Fast heart rate (tachycardia).

If you experience severe diarrhea accompanied by increasing muscle weakness or difficulty breathing, seek immediate medical attention. Your doctor may use a diagnostic tool called an edrophonium (Tensilon) test to distinguish between a cholinergic and myasthenic crisis.

Conclusion

For individuals with myasthenia gravis, Mestinon is an essential medication that can significantly improve muscle strength and quality of life. However, it's also well-established that the drug can cause diarrhea and other gastrointestinal side effects due to its effect on the nervous system. By understanding the underlying mechanism and working closely with a healthcare provider, patients can effectively manage these symptoms. Mild diarrhea often subsides with time, while more persistent issues can be addressed through dosage adjustments, dietary changes, and, in some cases, additional medication. Awareness of the more severe symptoms of a cholinergic crisis, including severe diarrhea and increased muscle weakness, is vital for ensuring patient safety. Through proactive management and open communication with your medical team, it is possible to minimize side effects and reap the full benefits of Mestinon therapy.

This information is for educational purposes only and is not a substitute for professional medical advice. For more detailed information on pyridostigmine, you can consult sources like the Bausch Health MESTINON prescribing information.

Frequently Asked Questions

Mestinon (pyridostigmine) works by increasing levels of acetylcholine, a neurotransmitter that aids muscle function but also stimulates the digestive system. This increased stimulation leads to faster intestinal muscle contractions (peristalsis), which can result in diarrhea.

Not necessarily. Mild to moderate diarrhea is a common side effect, especially when beginning treatment. However, severe or persistent diarrhea, particularly when combined with increasing muscle weakness, can be a symptom of a serious overdose known as a cholinergic crisis.

In many cases, the diarrhea and other gastrointestinal side effects are temporary and will lessen over a few days or weeks as your body gets used to the medication.

Yes, taking Mestinon with food is a common and effective strategy to help minimize gastrointestinal side effects like diarrhea and nausea. Some patients report that foods containing dairy or higher fat content are particularly helpful.

If the diarrhea is severe, persistent, or accompanied by increasing muscle weakness, you should contact your doctor immediately. They may need to adjust your dosage or investigate the possibility of a cholinergic crisis.

You should not take any over-the-counter anti-diarrheal medication, including Imodium (loperamide), without consulting your doctor first. While it can help, it may also mask important symptoms that signal an overdose.

Both conditions involve significant muscle weakness. A cholinergic crisis is an overdose of Mestinon and typically includes severe gastrointestinal symptoms like diarrhea. A myasthenic crisis is caused by an underdose or worsening of the disease and lacks these severe gastrointestinal side effects.