A dose of more than 750 milligrams of amitriptyline can cause severe toxicity in an adult, according to the Medicines and Healthcare Products Regulatory Agency. The risk of death as a result of amitriptyline overdose depends on the type of treatment administered to the patient.
Amitriptyline overdose can cause respiratory depression; a patient can stop breathing. Heart rhythm can also be affected, which could be fatal. The Medicines and Healthcare Products Regulatory Agency recommends giving activated charcoal within one hour to patients who consumed more than 4 milligrams of amitriptyline per kilogram of body weight to prevent absorption of the drug.