Does memantine cause diarrhea? Understanding This Common Side Effect

October 9, 2025 •

3 min read

In clinical trials, diarrhea was reported as a side effect in up to 5% of patients taking immediate-release memantine [1.2.1]. While not the most frequent adverse effect, the question of 'Does memantine cause diarrhea?' is a valid concern for patients and caregivers.

Quick Summary

Yes, memantine can cause diarrhea, though it is considered a less common side effect. This article examines the frequency of this and other GI issues, management tips, and how it compares to other Alzheimer's medications.

Key Points

Diarrhea is a Side Effect: Yes, memantine can cause diarrhea, affecting up to 5% of users in some studies [1.2.1].
Other GI Issues: Besides diarrhea, memantine may also cause constipation, nausea, vomiting, and abdominal pain [1.2.2, 1.3.8].
Management is Key: Managing diarrhea involves staying hydrated, dietary changes, and consulting a doctor before using OTC remedies [1.5.4].
Often Mild and Temporary: For many patients, side effects like diarrhea are mild and may lessen as their body gets used to the medication [1.2.4, 1.5.4].
Comparison to Other Drugs: Memantine is generally less likely to cause GI side effects like diarrhea compared to cholinesterase inhibitors such as donepezil [1.6.4, 1.6.6].
When to See a Doctor: Severe or persistent diarrhea, or diarrhea accompanied by fever or bloody stools, requires immediate medical attention [1.5.4].
Both Diarrhea and Constipation Possible: Uniquely, memantine lists both diarrhea and constipation as potential side effects with similar frequency [1.2.1].

Understanding Memantine and Its Purpose

Memantine, often known by its brand name Namenda, is a medication used to treat moderate to severe dementia associated with Alzheimer's disease [1.2.4]. It belongs to a class of drugs called NMDA (N-methyl-D-aspartate) receptor antagonists. Its primary function is to work on the brain's chemical messengers. In patients with Alzheimer's, there may be an excess of a chemical called glutamate, which can lead to nerve cell damage [1.2.4]. Memantine helps to regulate glutamate's activity, thereby slowing the progression of some symptoms of Alzheimer's disease [1.2.4]. It's important to note that it helps manage symptoms but does not cure the disease.

Does Memantine Cause Diarrhea?

Yes, diarrhea is a known side effect of memantine [1.2.2]. According to clinical trial data for the immediate-release formulation, approximately 5% of patients experienced diarrhea, compared to 4% in the placebo group [1.3.6]. Other sources list it as a common side effect, occurring in a range of 1% to 10% of users [1.2.2]. While other side effects like dizziness (7%), headache (6%), and confusion (6%) are slightly more common, diarrhea is a recognized gastrointestinal issue associated with the drug [1.2.1, 1.4.8].

The incidence can vary slightly depending on the formulation. For the extended-release version (Namenda XR), one study showed a 5% incidence of diarrhea versus 4% for placebo, indicating a similar risk profile to the immediate-release version [1.3.6].

Other Gastrointestinal Side Effects

Besides diarrhea, memantine can cause other issues within the gastrointestinal system. These are generally considered common, affecting between 1% and 10% of patients [1.4.2].

Constipation: Interestingly, constipation is also a common side effect, with some studies showing an incidence of 5%, similar to diarrhea [1.2.1, 1.3.8].
Nausea and Vomiting: Nausea and vomiting are also possible, though they may be less frequent than diarrhea or constipation [1.3.2, 1.4.3].
Abdominal Pain: General abdominal pain is another reported GI effect [1.2.2].
Pancreatitis: In rare, post-marketing reports, more severe issues like pancreatitis have been identified, though this is not a common occurrence [1.4.6].

Managing Diarrhea Caused by Memantine

If diarrhea occurs while taking memantine, it is often mild and may improve as the body adjusts to the medication [1.5.4]. However, there are several strategies to help manage the symptom:

Stay Hydrated: This is the most crucial step. Drink plenty of fluids like water, broth, or liquids containing electrolytes to prevent dehydration [1.5.1, 1.5.4].
Dietary Adjustments: Avoid foods that can worsen diarrhea, such as spicy, greasy, or high-fiber foods and dairy products [1.5.4].
Over-the-Counter (OTC) Medications: For mild cases, anti-diarrheal medications like loperamide (Imodium A-D) may be helpful for short-term use. It is always best to consult a pharmacist or doctor before starting any new medication [1.5.2, 1.5.4].
Communicate with the Doctor: If diarrhea is severe, persistent, or accompanied by other worrying symptoms like fever, severe abdominal pain, or blood in the stool, it is essential to contact the prescribing doctor immediately [1.5.4]. They may need to adjust the dosage or rule out other causes [1.5.6, 1.5.8].

Comparison with Other Alzheimer's Medications

Memantine is often compared to another class of Alzheimer's drugs called cholinesterase inhibitors, which includes donepezil (Aricept). When looking at side effects, there is a notable difference.


Side Effect Profile	Memantine (NMDA Antagonist)	Donepezil (Cholinesterase Inhibitor)
Primary Mechanism	Regulates glutamate [1.6.3]	Prevents breakdown of acetylcholine [1.6.3]
Common GI Side Effects	Dizziness, headache, confusion, constipation [1.6.6]	Diarrhea, nausea, vomiting, anorexia [1.6.1, 1.6.2, 1.6.7]
Diarrhea Frequency	Occurs, but generally less frequent than with ChEIs [1.6.4]	A more prominent and common side effect [1.6.1, 1.6.2]

Generally, cholinesterase inhibitors like donepezil are more commonly associated with gastrointestinal side effects such as nausea and diarrhea than memantine is [1.6.4, 1.6.6]. In fact, diarrhea is one of the most common side effects of donepezil [1.6.1].

Conclusion

So, does memantine cause diarrhea? The answer is yes, it is a recognized side effect, but it is not one of the most common, and its incidence is relatively low, affecting around 5% of users in clinical studies [1.2.1]. It can also cause other GI issues like constipation and nausea. These side effects are often mild and transient [1.2.4]. Management involves staying hydrated, adjusting diet, and consulting with a healthcare provider, especially if symptoms are severe. Compared to other Alzheimer's medications like donepezil, memantine is generally considered to have a lower risk of causing gastrointestinal disturbances [1.6.4].

For more detailed information, consult the official prescribing information from a reliable source like the FDA. Read more on the FDA-approved label.

Frequently Asked Questions

Diarrhea is reported in up to 5% of patients taking immediate-release memantine, making it a relatively common but not the most frequent side effect [1.2.1, 1.3.6].

You should drink plenty of fluids to avoid dehydration, avoid trigger foods, and speak with your doctor. They can provide guidance and rule out other causes. For mild cases, your pharmacist might suggest a short-term over-the-counter treatment [1.5.4].

Yes, constipation is also a common side effect of memantine, occurring with a similar frequency to diarrhea in clinical trials (around 3-5%) [1.3.8, 1.2.1].

No, the gastrointestinal side effects, including diarrhea, are typically mild and often temporary, improving as your body adjusts to the medication [1.2.4, 1.5.4].

You should not stop taking memantine without first consulting your healthcare provider. They can help you manage the side effect or determine if a change in treatment is necessary [1.5.6].

Diarrhea and other gastrointestinal issues like nausea are generally more common and prominent side effects of donepezil compared to memantine [1.6.2, 1.6.4].

You should contact your doctor immediately if diarrhea is severe, watery, contains blood, or is accompanied by high fever, severe stomach pain, or vomiting, as these could be signs of a more serious issue [1.5.4].