Memantine, sold under the brand name Namenda among others, is a medication used to slow the progression of moderate-to-severe Alzheimer's disease.

[15][16] Memantine is used to treat moderate-to-severe Alzheimer's disease, especially for people who are intolerant of or have a contraindication to AChE (acetylcholinesterase) inhibitors.

[17][18] One guideline recommends memantine or an AChE inhibitor be considered in people in the early-to-mid stage of dementia.

[19] Memantine has been associated with a modest improvement;[20] with small positive effects on cognition, mood, behavior, and the ability to perform daily activities in moderate-to-severe Alzheimer's disease.

[24] The UK National Institute for Clinical Excellence (NICE) issued guidance in 2018 recommending consideration of the combination of memantine with donepezil in those with moderate-to-severe dementia.

[20] Common adverse drug reactions (≥1% of people) include confusion, dizziness, drowsiness, headache, insomnia, agitation, and/or hallucinations.

[28] Despite isolated reports, recreational use of memantine is rare due to the drug's long duration and limited availability.

[30] A dysfunction of glutamatergic neurotransmission, manifested as neuronal excitotoxicity, is hypothesized to be involved in the etiology of Alzheimer's disease.

[34][35][36] The interaction of memantine with NMDA receptors plays a major role in the symptomatic improvement that the drug produces in Alzheimer's disease.

However, there is no evidence as yet that the ability of memantine to protect against extrasynaptic NMDA receptor-mediated excitotoxicity has a disease-modifying effect in Alzheimer's disease, although this has been suggested in animal models.

[37] Many 5-HT3 receptor antagonists function as antiemetics, however the clinical significance of this anti-serotonergic activity of memantine in Alzheimer's disease is unknown.

α7 nAChR upregulates quickly in response to antagonism, which could explain the cognitive-enhancing effects of chronic memantine treatment.

[8] Memantine was first synthesized, patented, and described by Eli Lilly and Company in 1963 as an anti-diabetic agent, but it was ineffective at lowering blood sugar.

[55] In 2000, Merz partnered with Forest to develop the drug for Alzheimer's disease in the United States under the brand name Namenda.

[58] In February 2014, as the July 2015 patent expiration for memantine neared, Actavis, which had acquired Forest, announced that it was launching an extended release (XR) form of memantine that could be taken once a day instead of twice a day as needed with the then-current "immediate release" (IR) version, and that it intended to stop selling the IR version in August 2014 and withdraw the marketing authorization.

In September 2014 the attorney general of New York, Eric Schneiderman, filed a lawsuit to compel Actavis to keep selling the IR version on the basis of antitrust law.

[64] It is a weak NMDA receptor antagonist and is reported to produce dissociative and phencyclidine (PCP)-like effects in animals and humans at sufficiently high doses.

[64] A study examining self-reported use of memantine on the social network Reddit showed that the drug was used both recreationally and as a nootropic, but also that it was misused in various illnesses as self-medication without strong scientific basis.

[67] As of August 2017, memantine is marketed under many brand names worldwide including Abixa, Adaxor, Admed, Akatinol, Alceba, Alios, Almenta, Alois, Alzant, Alzer, Alzia, Alzinex, Alzixa, Alzmenda, Alzmex, Axura, Biomentin, Carrier, Cogito, Cognomem, Conexine, Cordure, Dantex, Demantin, Demax, Dementa, Dementexa, Ebitex, Ebixa, Emantin, Emaxin, Esmirtal, Eutebrol, Evy, Ezemantis, Fentina, Korint, Lemix, Lindex, Lindex, Lucidex, Manotin, Mantine, Mantomed, Marbodin, Mardewel, Marixino, Maruxa, Maxiram, Melanda, Memabix, Memamed, Memando, Memantin, Memantina, Memantine, Mémantine, Memantinol, Memantyn, Memanvitae, Memanxa, Memanzaks, Memary, Memax, Memexa, Memigmin, Memikare, Memogen, Memolan, Memorel, Memorix, Memotec, Memox, Memxa, Mentikline, Mentium, Mentixa, Merandex, Merital, Mexia, Mimetix, Mirvedol, Modualz, Morysa, Namenda, Nemdatine, Nemdatine, Nemedan, Neumantine, Neuro-K, Neuroplus, Noojerone, Polmatine, Prilben, Pronervon, Ravemantine, Talentum, Timantila, Tingreks, Tonibral, Tormoro, Valcoxia, Vilimen, Vivimex, Witgen, Xapimant, Ymana, Zalatine, Zemertinex, Zenmem, Zenmen, and Zimerz.

[1] It is marketed in some countries as a combination drug with donepezil (memantine/donepezil) under the brand names Namzaric, Neuroplus Dual, and Tonibral MD.

[68] A 2008 systematic review concluded that although it was promising for such uses, memantine could not be recommended for such indications due to inadequate data.

[74] There are likewise limited data to support memantine in the treatment of schizophrenia based on systematic reviews and meta-analyses.

[84][85][86] Similarly to amantadine and dopamine receptor agonists, memantine reverses haloperidol-induced catalepsy and monoamine depletion-induced sedation in animals.

[95][96] Systematic reviews and meta-analyses published from 2016 to 2022 have found that memantine is not effective in the treatment of apathy in Alzheimer's disease and other dementias.