What to Know About Mestinon Side Effects

Starting a new medication always comes with questions — and Mestinon (Pyridostigmine Bromide) is no different. Like all medications, it can cause side effects. The good news is that most are mild, manageable, and tend to improve as your body adjusts.

This guide covers the common side effects, the serious ones to watch for, and practical tips for managing them. If you're about to start Mestinon or already taking it, knowing what to expect can help you feel more confident about your treatment.

What Is Mestinon?

Mestinon is a cholinesterase inhibitor that works by preventing the breakdown of acetylcholine, a chemical messenger that helps your muscles contract. It's primarily used to treat myasthenia gravis, a condition that causes muscle weakness. It's also prescribed off-label for POTS, orthostatic hypotension, and other autonomic conditions.

Because Mestinon increases acetylcholine levels throughout your body — not just at the muscles you want to target — it can affect your digestive system, salivary glands, sweat glands, and other organs. That's where most side effects come from.

Common Side Effects

These side effects are the most frequently reported. They're usually mild to moderate and often improve within a few days to weeks of starting treatment:

• Nausea — One of the most common complaints. Taking Mestinon with food or milk usually helps.
• Diarrhea — Increased gut activity is a direct result of higher acetylcholine levels.
• Abdominal cramps — Stomach cramping and discomfort, especially at higher doses.
• Increased salivation — You may notice more saliva production than usual.
• Increased sweating — Some patients experience noticeably more sweating.
• Muscle twitching (fasciculations) — Small, involuntary muscle twitches, usually harmless.
• Frequent urination — Acetylcholine stimulates the bladder, leading to more bathroom trips.
• Increased bronchial secretions — More mucus production in your airways.
• Blurred vision — Typically mild and temporary.
• Watery eyes — Increased tear production.
• Vomiting — Less common than nausea but can occur, especially with higher doses.

Most of these side effects are dose-related — meaning they tend to get worse at higher doses and better at lower doses. Your doctor can adjust your dose to find the right balance between symptom relief and side effects.

Serious Side Effects

Serious side effects from Mestinon are uncommon but require immediate medical attention:

• Cholinergic crisis — This is the most important one to know about. If you take too much Mestinon, acetylcholine levels can become dangerously high, causing severe muscle weakness, difficulty breathing, excessive secretions, and potentially respiratory failure. A cholinergic crisis can look similar to a myasthenic crisis (worsening of MG symptoms), which is why it's critical to seek emergency care — the treatments are very different.
• Bradycardia — A slow heart rate. If you feel dizzy, faint, or notice your heart rate dropping significantly, contact your doctor.
• Bronchospasm — Tightening of the airways, which can cause wheezing or difficulty breathing. This is more concerning for patients with asthma.
• Hypotension — Low blood pressure, which can cause lightheadedness or fainting.
• Severe allergic reactions — Rare, but signs include rash, swelling of the face or throat, and difficulty breathing.
• Cardiac arrest — Extremely rare, typically associated with significant overdose.

When to call your doctor or 911:

• Severe muscle weakness that's getting worse instead of better
• Difficulty breathing or swallowing
• Excessive drooling, sweating, or tearing that feels uncontrollable
• Heart rate below 50 beats per minute
• Fainting or near-fainting
• Any signs of an allergic reaction

Side Effects in Specific Populations

Pregnancy

Mestinon is classified as pregnancy risk equivalent to Category C. It should be used during pregnancy only if clearly needed. Pyridostigmine can cross the placenta, and there have been reports of temporary muscle weakness in newborns of mothers taking the medication. If you're pregnant or planning to become pregnant, discuss the risks and benefits with your neurologist.

Breastfeeding

Pyridostigmine is excreted in breast milk. While it's generally considered compatible with breastfeeding at typical doses, you should discuss this with your doctor and monitor your baby for any signs of GI upset or unusual fussiness.

Older Adults

Elderly patients may be more sensitive to the cholinergic effects of Mestinon, including digestive side effects and changes in heart rate. Lower starting doses and slower dose increases are often recommended.

Kidney Impairment

Pyridostigmine is partially eliminated by the kidneys. If you have kidney disease, your doctor may need to adjust your dose to prevent side effects from drug accumulation.

How to Manage Side Effects

Here are practical strategies that many Mestinon patients find helpful:

• Take it with food — This is the single most effective way to reduce nausea, cramping, and diarrhea. A small snack or glass of milk is usually enough.
• Start low, go slow — If you're just starting Mestinon, your doctor will likely begin with a low dose (often 30–60 mg) and gradually increase. This gives your body time to adjust.
• Space your doses evenly — Taking Mestinon at regular intervals (every 4–6 hours) helps maintain steady acetylcholine levels and reduces peaks that cause side effects.
• Keep a symptom diary — Track when you take each dose, what you eat, and any side effects. This helps your doctor fine-tune your dosing schedule.
• Stay hydrated — Diarrhea and sweating can lead to fluid loss. Drink plenty of water throughout the day.
• Talk to your doctor about timing — Some patients find that taking the extended-release formulation (Mestinon Timespan 180 mg) at bedtime reduces daytime GI side effects while providing overnight muscle support.

If side effects are interfering with your quality of life, don't adjust your dose on your own. Talk to your doctor — there are usually ways to modify the regimen without sacrificing symptom control. You can also learn more about how Mestinon works to better understand why these side effects happen.

Final Thoughts

Mestinon is a well-established medication that has helped millions of people with myasthenia gravis and other conditions. While side effects are common — especially GI symptoms — most patients find they're manageable with simple strategies like taking the medication with food and starting at a low dose.

The key is knowing the difference between expected side effects and warning signs that need medical attention. If you experience severe weakness, breathing difficulties, or a very slow heart rate, seek help immediately.

If you're having trouble finding Mestinon at your pharmacy, Medfinder can help you check stock near you so you don't miss a dose.