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Deaths have been reported from overdose with amantadine. The lowest reported acute lethal dose was 2 grams.
Amantadine has been associated with several central nervous system (CNS) side effects, likely due to amantadine's dopaminergic and adrenergic activity, and to a lesser extent, its activity as an anticholinergic. CNS side effects include nervousness, anxiety, agitation, insomnia, difficulty in concentrating, and exacerbations of pre-existing seizure disorders and psychiatric symptoms in patients with schizophrenia or Parkinson's disease. The usefulness of amantadine as an anti-parkinsonian drug is somewhat limited by the need to screen patients for a history of seizures and psychiatric symptoms.
Rare cases of severe skin rashes such as Stevens Johnson Syndrome[14] and suicidal ideation in patients treated with amantadine have also been reported.[15][16]
Livedo reticularis is a possible side effect of amantadine use for Parkinson's disease.[17]