Memantine Side Effects: What to Expect and When to Call the Doctor

If a doctor has prescribed memantine (brand name Namenda) for moderate to severe Alzheimer’s disease, you’re probably trying to figure out what to expect in the weeks ahead — both for the person taking it and for you, if you’re the one helping manage their care. Memantine works differently from the cholinesterase inhibitors like donepezil that are often prescribed earlier in the disease, and its side effect profile reflects that difference. Here’s what the clinical data actually shows.

What Memantine Is Used For

Memantine is an NMDA receptor antagonist, a different class of medication from the cholinesterase inhibitors (donepezil, rivastigmine, galantamine) typically used earlier in Alzheimer’s disease. Rather than boosting acetylcholine levels, memantine works by regulating glutamate activity in the brain, which is thought to play a role in the nerve cell damage seen in Alzheimer’s disease. It’s approved specifically for moderate to severe Alzheimer’s disease and is often prescribed alongside a cholinesterase inhibitor, since the two medications work through different mechanisms and can be combined to address different aspects of the disease process as it progresses.

Most Common Side Effects

According to professional prescribing data, the most common side effects — each occurring in at least 5% of patients and more frequently than with a placebo — are dizziness, headache, confusion, constipation, and diarrhea. A second tier of side effects, generally occurring in 1% to 10% of patients, includes:

• Fatigue
• Insomnia
• Hallucinations
• Anxiety and agitation
• Depression
• Cough and shortness of breath
• Nausea and vomiting
• Abdominal pain
• Urinary incontinence and urinary tract infection
• Falls
• Weight changes

A separate consumer-facing list also notes dry mouth, sleepiness, trouble concentrating, restlessness, and back pain as effects some patients report, even where formal incidence percentages aren’t available. As with most dementia medications, these effects can be harder for the person taking the drug to report clearly themselves, which is part of why caregivers play such an important role in noticing and tracking changes.

Less Common and Serious Side Effects

Beyond the common effects above, memantine carries a smaller set of less common but more serious risks:

• Seizures, listed as uncommon (roughly 0.1% to 1% of patients).
• Heart failure and venous thrombosis (blood clots in the veins), both listed as uncommon.
• Fungal infections, also listed in the uncommon category.
• Severe skin reactions, including Stevens-Johnson syndrome and skin blistering or peeling, reported rarely or through postmarketing surveillance rather than clinical trials specifically.
• Liver problems, including hepatitis and yellowing of the skin or eyes, and pancreatitis, both reported rarely.
• Blood disorders, including low white blood cell counts, agranulocytosis, and thrombotic thrombocytopenic purpura, reported through postmarketing data.
• Acute kidney failure, reported rarely.
• Psychotic reactions, reported through postmarketing surveillance.

These more serious effects are uncommon to rare, but their range is part of why ongoing medical follow-up matters throughout treatment, not just during the first few weeks.

Symptoms That Need Prompt Medical Attention

Certain symptoms should prompt a call to the doctor right away rather than waiting for a routine visit: swelling of the face, arms, legs, or feet; rapid weight gain; blurred vision; an abnormal or irregular heartbeat; or tingling in the hands or feet. Fainting, loss of consciousness, a seizure, or chest pain are more urgent still and warrant emergency care. Psychiatric changes — including new depression, hostility, or seeing or hearing things that aren’t there — are also worth reporting promptly, since postmarketing data includes reports of suicidal thoughts associated with the medication. As a caregiver, you may notice these changes before the person taking memantine is able to describe or recognize them, which makes your observations genuinely important to share with the care team.

How Memantine Compares to Cholinesterase Inhibitors

Memantine is often discussed alongside donepezil and the other cholinesterase inhibitors, but the two classes have meaningfully different side effect profiles. Cholinesterase inhibitors like donepezil are more associated with digestive symptoms (diarrhea, nausea) and, less commonly, heart rate and rhythm effects, since they work through the acetylcholine pathways that also regulate heart rate. Memantine’s most common effects — dizziness, headache, confusion, and constipation — reflect its different mechanism and are generally considered somewhat easier for patients to tolerate overall, though “easier to tolerate” doesn’t mean risk-free, as the list above shows. If you’re also managing a cholinesterase inhibitor prescription, our guide to donepezil side effects covers that medication’s distinct profile for comparison.

Why These Two Medications Are Often Combined

Because memantine and cholinesterase inhibitors work through different biological mechanisms, doctors sometimes prescribe them together for moderate to severe Alzheimer’s disease, on the reasoning that addressing both the acetylcholine and glutamate systems may provide more complete symptom management than either medication alone. This combination approach is a clinical judgment made by the prescribing doctor based on the disease stage, how well each medication is tolerated individually, and the specific symptoms being targeted — it isn’t automatic for every patient, and some people do well on just one of the two.

Caregiver Tips for Managing Memantine

If you’re helping manage memantine for someone else, a few practical habits can make side effect tracking and doctor visits more productive:

• Keep a simple symptom log, noting dizziness, confusion, bowel changes, falls, and sleep patterns, especially during the first several weeks and after any dose adjustment.
• Watch for falls specifically, since dizziness and confusion both raise fall risk, and falls are themselves listed as a recognized side effect — consider discussing home safety modifications with the care team if falls occur or seem likely.
• Note any new psychiatric symptoms, including agitation, hallucinations, or withdrawal, since these can be harder for the person to report themselves and are specifically flagged as symptoms to communicate to the doctor.
• Bring a complete, current medication list to every appointment, including over-the-counter drugs, supplements, and herbal products, since the prescribing information specifically advises against adding anything new without checking with the doctor first.
• Don’t adjust the dose without talking to the doctor, even if side effects are frustrating, since dose changes should generally be made gradually and under medical guidance.

Regular Monitoring Matters Throughout Treatment

Because memantine’s more serious risks — including kidney, liver, and blood-related effects — tend to develop or surface over time rather than immediately, regular follow-up visits are part of using this medication safely, not an optional extra. These visits are the mechanism by which a doctor catches early signs of these less common complications before they become more serious, and they’re also the opportunity to reassess whether the current dose and combination of medications still make sense as the disease progresses.

How Memantine Dosing Typically Works

Memantine is generally started at a low dose and increased gradually over several weeks, rather than beginning at the full target dose right away — a titration schedule specifically designed to reduce the intensity of side effects like dizziness and confusion while the body adjusts. A typical pattern involves starting with a small dose once daily, then increasing the dose roughly once a week until reaching the target dose, which may end up being taken once or twice daily depending on the specific formulation prescribed (immediate-release tablets are usually taken twice daily, while extended-release capsules are typically once daily). If side effects become bothersome at any point during this titration period, the prescribing doctor may choose to slow the increase, hold at a lower dose longer, or in some cases pause the titration altogether rather than pushing through to the target dose on the original schedule. This is also why missing several doses in a row matters more than it might with some other medications: restarting after an extended gap sometimes means restarting the titration process from a lower dose rather than resuming at the previous level, so it’s worth checking with the prescribing doctor or pharmacist if doses have been missed for several days or more.

What the Research Says About Effectiveness

Memantine doesn’t reverse or cure the underlying neurodegeneration of Alzheimer’s disease, and it’s important to set expectations accordingly. Clinical trials supporting its approval showed modest but measurable benefits in cognitive function, daily living activities, and behavior for patients with moderate to severe disease, compared to those taking a placebo — benefits that tend to show up as a somewhat slower rate of decline rather than an improvement back to an earlier stage of functioning. Because Alzheimer’s disease itself continues to progress even with treatment, families and caregivers sometimes feel disappointed if they’re expecting the medication to produce a visible improvement rather than a slower decline, so it’s worth discussing realistic expectations with the prescribing doctor before starting, and periodically reassessing together whether the medication still seems to be providing meaningful benefit as the disease progresses.

Frequently Asked Questions

How soon do memantine side effects typically appear?

The most common side effects, including dizziness, headache, and confusion, generally appear within the first days to weeks of starting the medication or after a dose increase, though individual timing varies. Any side effect that’s significant or concerning is worth reporting to the doctor rather than waiting it out.

Can memantine make confusion or dementia symptoms worse?

Confusion is itself listed as a common side effect of memantine, which can sometimes be difficult to distinguish from the underlying disease’s own progression. If confusion noticeably worsens after starting or increasing the medication, this is worth discussing with the prescribing doctor rather than assuming it’s simply the disease advancing.

Is memantine safe to take with donepezil?

Yes, this combination is commonly prescribed for moderate to severe Alzheimer’s disease, since the two medications work through different mechanisms. Whether it’s the right choice for a specific patient is a decision made by the prescribing doctor based on disease stage and individual tolerance.

What should I do if a dose of memantine is missed?

General guidance for missed doses of regularly scheduled medications is to take it as soon as remembered unless it’s close to the time of the next dose, in which case the missed dose is typically skipped rather than doubled up. Confirm specific guidance with the prescribing doctor or pharmacist, especially if you’re managing medication for someone else.

Does memantine cause weight loss or weight gain?

Weight changes are listed among the less common side effects, without a clearly predictable direction for most patients. If significant weight change occurs, it’s worth mentioning at the next appointment, since it could reflect the medication, the underlying disease, or an unrelated cause worth investigating.

Can memantine be stopped safely if side effects are too bothersome?

This should be discussed with the prescribing doctor rather than decided independently, since stopping dementia medications can sometimes affect symptom control, and the doctor may want to try a dose adjustment or additional monitoring before considering discontinuation.

Why does my loved one need regular blood tests while on memantine?

Because some of memantine’s less common but serious risks involve the kidneys, liver, and blood cells, regular monitoring through follow-up visits and occasional lab work helps catch these issues early, well before they would otherwise become noticeable or symptomatic.

This article is for general educational purposes and isn’t a substitute for personalized medical advice. Always talk with the prescribing doctor or pharmacist about specific symptoms, medical history, and medication questions, and never stop or adjust a prescribed medication without medical guidance.

Memantine is generally considered a well-tolerated option within dementia care, and most patients manage its common side effects — dizziness, headache, confusion, and digestive changes — without major disruption. Its less common but more serious risks are exactly why regular follow-up visits matter throughout treatment, not just at the start. For caregivers in particular, knowing what to watch for and reporting changes promptly makes the biggest difference in using this medication safely as part of a broader Alzheimer’s care plan.