How long does Namenda stay in your system? (+3 factors)

In this article, we will discuss the stay of Namenda in your system. We will also discuss some factors which may affect the stay of Namenda in your system and the withdrawal symptoms if you discontinue the use of Namenda abruptly.

How long does Namenda stay in your system?

Namenda may stay in your body for about a week after the last dose is taken. Namenda has a terminal half-life of 60-80 hours. The average peak plasma concentration is achieved within 3-7 hours.

The stay of Namenda in the system may vary depending on the age, weight, dosage strength, dosing frequency, concomitant administration of other drugs, and other underlying health conditions.

Patients with renal and liver disease may require dose adjustment. Most of the drug (75-90% of the dose) is eliminated via the kidney as an unchanged form of Namenda. Therefore, it may require several days to achieve steady plasma drug concentration (1).

What is the half-life of Namenda?

The half-life of Namenda is 60-80 hours. This means that the drug requires 60-80 hours to reduce to half of its initial drug concentration. After this time, the remaining concentration further reduces to half in the next 60-80 hours.

This process continues until all of the drug is excreted from your system. Namenda may require up to three months to start working, but the onset of action varies from one person to another.

Factors affecting the time taken by Namenda to leave your system

Several factors can affect the stay time of Namenda in your system, including:


The initial dose of Namenda is 5 mg/day which can be increased to 20 mg/day. Higher doses of Namenda generally require more time to get eliminated from the body as compared to the lower dose.

Genitourinary condition

Conditions that raise the pH of urine decrease the urinary elimination of Namenda. The plasma concentration of Namenda hence increases. This increases the plasma concentration of the drug and prolongs its stay in the body (2).

Severe hepatic impairment

The dose of Namenda should be adjusted if the patient has severe hepatic impairment. However, dose adjustment is not required in the case of mild or moderate liver dysfunction (3).

Severe renal impairment

Severe renal impairment may reduce the clearance of Namenda from your system, especially under alkaline conditions. However, dose adjustment is not required in the case of mild to moderate renal dysfunction (4).

Drugs which make urine alkaline

Drugs, such as carbonic anhydrase inhibitors and sodium carbonate make the urine alkaline. This may increase the accumulation of Namenda in the system as alkaline pH decreases the urinary elimination of Namenda.

Age and gender

The elimination rate of Namenda may be affected by age and gender due to the overall health condition of the patient. However, such changes are not significant. Dose adjustment is necessary in the elderly with liver and renal dysfunction (5).


Coadministration of Namenda with sertraline may induce a pronounced antidepressant effect than either drug used alone. This increases the stay of Namenda in the system and increases the risk of side effects associated with sertraline such as fatigue and night sweats (6).

Can Namenda cause withdrawal symptoms?

Namenda can cause withdrawal symptoms so you should not stop taking Namenda abruptly. You should talk to your doctor if you feel your condition is not improving or side effects are affecting your quality of life (7).

Withdrawal symptom Effect
Cognitive disturbance Memory impairment, trouble following a conversation, and social phobia.
Insomnia Sleep disturbance includes difficulty in falling asleep, waking up frequently, irritation, and feeling tired after waking up.
Worsening of neuropsychiatric problems Anxiety, mood swings, sleep disturbance, and possible tic disorder.
Aggressive behaviour Disorganized thinking, irritability, poor judgement, and threatening behaviour.
Visual hallucinations Seeing objects move when they are stagnant and seeing complex scenarios of people that are not present.

What to do if Namenda is not working?

Namenda is prescribed to treat moderate to severe dementia due to Alzheimer’s disease. Namenda may take up to three months to show its effect. After three months if you still think Namenda is not working for you then consult your doctor.

Talk to your doctor

If Namenda is not working for you or your condition is worsening even after taking a high dose of Namenda, your doctor may prescribe you another medication. But first, he will take your medical history and identify the possible reason why Namenda is not showing its desired effects.

Alternatives to Namenda

The Food and Drug Administration (FDA) has approved five medications for the management of dementia associated with Alzheimer’s disease, including Namenda, donepezil, tacrine, galantamine, and rivastigmine.

Except for Namenda, the rest of the drugs belong to the class of acetylcholinesterase inhibitors (AchEI). These drugs are prescribed for mild to moderate Alzheimer’s disease. However, donepezil can be used for the treatment of advanced stages of Alzheimer’s disease.

As a pharmacist, I would advise you to follow the directions of your doctor for the safe and effective use of Namenda. Although, you may not feel any changes at first, with time your condition will begin to improve.

Was this helpful?

Thanks for your feedback!



Beconi MG, Howland D, Park L, Lyons K, Giuliano J, Dominguez C, Munoz-Sanjuan I, Pacifici R. Pharmacokinetics of memantine in rats and mice. PLoS Currents. 2011 Dec 15;3.


HBr G. Drugs to treat aLZHeIMer’s DIsease.


Lammert C, Einarsson S, Saha C, Niklasson A, Bjornsson E, Chalasani N. Relationship between daily dose of oral medications and idiosyncratic drug‐induced liver injury: search for signals. Hepatology. 2008 Jun;47(6):2003-9.


Periclou A, Ventura D, Rao N, Abramowitz W. Pharmacokinetic study of memantine in healthy and renally impaired subjects. Clinical Pharmacology & Therapeutics. 2006 Jan;79(1):134-43.


Noetzli M, Guidi M, Ebbing K, Eyer S, Wilhelm L, Michon A, Thomazic V, Alnawaqil AM, Maurer S, Zumbach S, Giannakopoulos P. Population pharmacokinetic study of memantine: effects of clinical and genetic factors. Clinical pharmacokinetics. 2013 Mar;52:211-23.


Amidfar M, Réus GZ, Quevedo J, Kim YK, Arbabi M. Effect of co-administration of memantine and sertraline on the antidepressant-like activity and brain-derived neurotrophic factor (BDNF) levels in the rat brain. Brain Research Bulletin. 2017 Jan 1;128:29-33.


Kwak YT, Han IW, Suk SH, Koo MS. Two cases of discontinuation syndrome following cessation of memantine. Geriatrics & gerontology international. 2009 Jun;9(2):203-5.