A lethal dose of Ambien in rats is 600 milligrams per kilogram, according to Safety Medical, which implies that to cause death, the drug would have to be ingested in large quantities. However, Ambien can affect the heart and breathing, causing fatal complications at much lower doses.
The US Food and Drug Administration has ruled that any dosage above 15 milligrams is categorized as an overdose. According to WebMD, side effects include memory loss, blackouts and mood swings including suicidal tendencies. The drug has a history of causing sleep-driving, a condition where a person not fully awake decides to drive a vehicle, which may lead to fatality.