The lethal dose of arsenic for human beings ranges from 100 milligrams to 300 milligrams of inorganic arsenic. The Risk Assessment Information System database estimates the acute lethal dose of inorganic arsenic at 0.6 milligrams per kilogram per day. Inorganic arsenic is 500 times more dangerous than its organic counterpart.
Death occurs within 24 hours to four days depending on the amount ingested. Small amounts under 5 milligrams are not lethal and symptoms typically resolve after about 12 hours. Arsenic's historical use as a poison is documented as early as the fourth century B.C.E. Arsenic was the most common compound used for poison from the Roman Empire to the Renaissance.