An overdose of modafinil can lead to a range of symptoms and complications. Psychiatric symptoms may include psychosis, mania, hallucinations, and suicidal ideation, which can occur even in individuals without a history of mental illness and may persist after discontinuation of the drug. Neurological complications, such as seizures, tremors, dystonia, and dyskinesia, may arise from modafinil's interaction with various neurotransmitter systems.
Allergic reactions such as rash, angioedema, anaphylaxis, and Stevens–Johnson syndrome may be triggered by an immunological response to modafinil or its metabolites. Cardiovascular complications like hypertension, tachycardia, chest pain, and arrhythmias may also be observed due to modafinil's sympathomimetic action.
In animal studies, the median lethal dose (LD) of modafinil varies among species and depends on the route of administration. In mice and rats, the LD is approximately  if administered via an injection, but the oral LD for rats is . The LD value for humans have not been established. Human clinical trials have involved total daily doses up to  for 7–21 days. Acute one-time total overdoses up to  have not been life-threatening but resulted in symptoms like agitation, insomnia, tremor, palpitations, and gastrointestinal disturbances.
The management of modafinil overdose involves supportive care, monitoring of vital signs, and treatment of specific complications. In cases of recent consumption, activated charcoal, gastric lavage, or hemodialysis may be used. There is no specific antidote for modafinil overdose. The main way to deal with modafinil overdose is supportive care, which includes sedating the patient and stabilizing their blood pressure, and muscle activity in case of manifestations such as agitation or tremor.