8 Memantine (Namenda) Side Effects: How to Manage Headaches, Diarrhea, and More

Alzheimer's disease is the most common form of dementia. Treatments that target the underlying disease process are now available. But there are also medications that can help with symptoms, such as memory loss and attention problems. Of these options, memantine (Namenda) is one that works differently.

Memantine is typically reserved for moderate-to-severe Alzheimer’s-related dementia. And it’s usually taken in combination with other medications for additive treatment effects. Most people are able to tolerate memantine, but they may experience some dizziness while taking it. So, what other side effects can you or your loved one expect?

Memantine side effects at a glance

Generally, memantine is safe and well-tolerated. Most of its side effects are mild and can be managed without needing to stop the medication. And although memantine comes in several different oral dosage forms, the side effects are similar — no matter which form you’re taking. 

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Mild memantine side effects can include:

• Headache

• Dizziness

• Constipation

• Diarrhea

• Drowsiness

• Back pain

More serious memantine side effects can include:

• Elevated blood pressure

• Cardiovascular effects, such as a slowed heart rate (bradycardia)

• Confusion

• Hallucinations

• Agitation

• Intense dreaming

• Mood changes

Below, we cover what you should know about eight notable memantine side effects, including potential causes and management tips.

1. Headache

Headache is one of the most common memantine side effects. However, memantine is often taken with other Alzheimer’s medications that commonly cause headaches, such as donepezil (Aricept, Adlarity). So, it’s possible that memantine may not be the true or only cause. 

But if you or your loved one are getting headaches while taking memantine, they may improve over time with continued use. In the meantime, you can try to manage headaches at home. Be sure to drink enough fluids, since dehydration can contribute to headaches. If needed, your pharmacist can recommend an over-the-counter (OTC) pain reliever that’s safe for you to take.

If OTC pain medications don’t help, or if your headaches continue or get worse, notify your prescriber. They may need to evaluate your headaches further and adjust your medication regimen.

2. Dizziness

Dizziness is another common memantine side effect. Most people know they’re dizzy when they stand up and feel unsteady — like the world is moving beneath them. Others may describe feeling lightheaded or “off.”

When it comes to dizziness, it’s best to be extra careful. Dizziness can lead to falls and injury. If you’re feeling dizzy while taking memantine, it’s best to lie down and rest until you’re feeling better. Once you’re ready to get back up, make sure to do so slowly. Getting up too quickly may make you feel worse. Call for help if you don’t think you can move around safely on your own.

Contact your prescriber if your dizziness is getting worse or not going away. Since dizziness can have many causes, they can figure out the best next steps. And if you’re taking memantine once a day, they may suggest taking your dose in the evening to see if that helps.

3. Constipation

Some people may become constipated while taking memantine. This is usually mild, temporary, and manageable at home. To keep things moving, here are some tips to prevent constipation:

• Add more fiber to your diet.

• Drink enough water.

• Safely increase your physical activity.

• Don’t put off the urge to use the bathroom.

• Keep a regular bathroom schedule.

An OTC laxative is another option if these methods aren’t working. Your pharmacist can recommend one that’s best for you or your loved one’s situation. They can also help identify other medications being taken that may worsen constipation.

But if laxatives aren’t helping, or if you’re experiencing pain from constipation, notify your prescriber. You’ll need some additional guidance on treating your constipation. 

4. Diarrhea

While some people experience constipation with memantine, others may have the opposite problem — diarrhea. But it’s possible that this side effect may be from another Alzheimer’s medication you’re taking with memantine instead.

If you’re experiencing diarrhea with memantine, the symptoms should be mild and improve with continued use. In the meantime, you can manage your diarrhea with anti-diarrheal medications. Your pharmacist can help you pick one that best meets your needs.

Be sure you’re drinking enough liquids to replace the fluids and electrolytes you lose when you have diarrhea — especially persistent diarrhea. It’s also best to avoid or minimize trigger foods that can make diarrhea worse, such as dairy products or spicy or greasy foods.

If your diarrhea is severe or accompanied by any of the following symptoms, contact your prescriber right away:

• Severe abdominal pain

• Fever 

• Changes in stool color (red or black stool may be a sign of internal bleeding) 

• Severe bloating or vomiting

• Severe weakness 

In these cases, your diarrhea may be related to other health conditions. Your prescriber will be able to evaluate your symptoms.

5. Drowsiness

Memantine may make you feel drowsy or sleepy. For some people, this may be a welcome side effect. In fact, a small study found that memantine helped people with Alzheimer’s disease sleep longer and not wake up as much at night. But more research is needed to confirm this effect.

However, feeling drowsy during the day can interfere with daily activities. So, it’s best to avoid tasks that require you to be alert until the drowsiness improves. Your healthcare team can also review your medication list, since several medications may worsen this side effect.

Talk to your prescriber if the drowsiness isn’t going away or is difficult to manage. If you or your loved one are taking memantine once daily in the morning, they may have you try taking it at night to see if that makes a difference.

6. Back pain

One of memantine’s less frequent side effects is back pain. You may notice new or worsening pain when starting memantine, which may improve over time.

But until the symptoms resolve, OTC pain medications may help. And if the pain is too severe to deal with on your own, notify your prescriber. They will be able to assist with next steps in pain management for you or your loved one.

Good to know: Chronic pain may be linked to dementia. Because of this, it may be hard to determine whether the pain is due to a memantine side effect or Alzheimer’s.

7. Cardiovascular effects

Memantine may cause an increase in blood pressure. If you already have high blood pressure, your prescriber may keep a closer eye on your readings after you start memantine. They may adjust your blood pressure medications if your readings get too high.

Alzheimer’s medications, including memantine, may also increase the risk of other cardiovascular effects, such as bradycardia. This risk may be higher if you have certain health conditions, including heart rhythm problems or kidney disease. Depending on your health history and the medications you take, your prescriber will determine if memantine is appropriate.

8. Mental status changes

Memantine can help improve behavioral symptoms associated with Alzheimer’s disease, such as agitation and aggression. But some people taking it may experience confusion, hallucinations, and mood changes. Intense dreaming and agitation have also been reported on rare occasions.

Determining if these changes are directly related to memantine may be tricky. This is because dementia itself leads to mental status changes. And mental status decline progresses over the course of the condition. If it’s caused by memantine, these side effects usually resolve after your prescriber tells you or your loved one to stop taking it.

Nonetheless, mental health-related effects from memantine shouldn’t be taken lightly. Confusion, agitation, and hallucinations can have serious consequences. Notify your prescriber regarding any notable changes in mental status. But don’t stop taking memantine unless instructed to do so.

When should you contact your prescriber about memantine side effects?

Memantine’s side effects are generally mild and usually improve over time. But in the meantime, your healthcare team can recommend OTC medications and lifestyle changes for relief. Tell them if any side effects are getting worse or aren’t going away.

Make sure that your healthcare team has your current medication list. In some cases, certain medications may worsen memantine side effects, such as drowsiness or constipation. Your care team can help identify potential interactions and advise on how to manage them.

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Written by:

Niousha Nader, PharmD, BCCCP

Niousha Nader, PharmD, BCCCP is a critical care and geriatric specialist. She has over 12 years of hospital experience, which also includes pediatric, emergency, surgical, and oncologic pharmacy.

Edited by:

Alyssa Billingsley, PharmD

Alyssa Billingsley, PharmD, is the director of pharmacy content for GoodRx. She has over a decade of experience as a pharmacist and has worked in clinical, academic, and administrative roles.

Reviewed by:

Joshua Murdock, PharmD, BCBBS

Joshua Murdock, PharmD, BCBBS, is a licensed pharmacist in Arizona, Colorado, and Rhode Island. He has worked in the pharmacy industry for more than 10 years and currently serves as a pharmacy editor for GoodRx.

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