"Tetrahydrocannabinol is a very safe drug. Laboratory animals (rats, mice, dogs, monkeys) can tolerate doses of up to 1000 mg/kg (milligrams per kilogram). This would be equivalent to a 70 kg person swallowing 70 grams of the drug —about 5,000 times more than is required to produce a high. Despite the widespread illicit use of cannabis there are very few if any instances of people dying from an overdose."
Iversen, Leslie L., "The Science of Marijuana" Oxford University Press (New York, NY: 2000), p. 178.