There has never been a documented human fatality from overdosing on tetrahydrocannabinol or cannabis.[15] Information about THC's toxicity is derived from animal studies. The toxicity depends on the route of administration and the laboratory animal. Absorption is limited by serum lipids, which can become saturated with THC, mitigating toxicity.[16] According to the Merck Index, 12th edition, THC has a LD50 (dose killing half of the research subjects) value of 1270 mg/kg (male rats) and 730 mg/kg (female rats) administered orally dissolved in sesame oil.[17] The LD50 value for rats by inhalation of THC is 42 mg/kg of body weight.[17]
One estimate of THC's LD50 for humans indicates that about 1500 pounds (680 kilograms) of cannabis would have to be smoked within 14 minutes.[18] This estimate is supported by studies which indicate that the effective dose of THC is at least 1000 times lower than the estimated lethal dose (a "safety ratio" of 1000:1). This is much higher than alcohol (safety ratio of 10:1), cocaine (15:1), or heroin (6:1).[19]