Memantine Dosage Guide

## Can You Fatally Overdose on Memantine? Fatal memantine overdose is extremely unlikely. Case reports describe survival after ingestions of 400 mg and above, with supportive care. No confirmed deaths from memantine alone appear in the medical literature. The wide therapeutic index that makes it suitable for elderly Alzheimer's patients also provides a large margin between recreational doses and life-threatening toxicity. However, severe memantine intoxication can produce effects that require medical management and that are genuinely dangerous in context. ## Recognizing Severe Intoxication At very high doses (typically 200+ mg, though individual variation applies): - **Psychomotor agitation** -- restlessness, pacing, inability to stay still, sometimes progressing to frank agitation that can lead to injury - **Confusion and disorientation** -- the person may not know where they are, what day it is, or what they have taken. Given the 2-4 day duration, this can persist long enough to become a serious practical problem - **Visual disturbances** -- diplopia (double vision), nystagmus, altered depth perception - **Stupor** -- at extreme doses, prolonged sedation with reduced responsiveness - **Hallucinations** -- reported at high doses, generally mild compared to other dissociatives but disorienting in context - **Tachycardia and hypertension** -- cardiovascular stimulation, usually mild ## What To Do For mild to moderate overingestion (uncomfortable but responsive and oriented): - **Wait it out in a safe environment** -- there is no specific antidote and the primary treatment is supportive. The long half-life means this may take 2-4 days - **Stay hydrated** -- maintain fluid intake - **Avoid driving or operating machinery** for at least 72 hours after a large dose - **Monitor for worsening symptoms** -- if confusion deepens, agitation becomes unmanageable, or the person becomes unresponsive, seek medical attention For severe intoxication (unresponsive, severely confused, agitated, or showing cardiovascular instability): - **Call emergency services** -- tell them it was memantine (an NMDA receptor antagonist) and the approximate dose - **There is no specific antidote** -- treatment is entirely supportive: IV fluids, monitoring, benzodiazepines for agitation or seizures, and observation - **Acidification of urine** can accelerate renal elimination, though this is a hospital intervention, not a home remedy - **Activated charcoal** may be useful if administered within 1-2 hours of ingestion ## The Duration Problem The most practically dangerous aspect of memantine overdose is not acute toxicity but the sheer duration of impairment. Being cognitively impaired and mildly dissociated for 72+ hours creates cumulative risks: driving accidents, workplace errors, impaired judgment in social situations, and the slow erosion of the person's confidence that they will return to normal. Reassurance that the effects will resolve -- because they will -- is an important component of care. ## Combination Risks The already-long duration of memantine makes combinations with other long-acting substances (extended-release stimulants, long-acting benzodiazepines, methadone) particularly problematic, as the window of overlapping effects extends for days rather than hours. Most memantine-related medical concerns described in community reports involve combinations rather than memantine alone.