The toxicity of LSD has been determined in various animal species. A standard for the toxicity of a substance is the LD50, or the median lethal dose, that is, the dose with which 50 percent of the treated animals die. In general it fluctuates broadly, according to the animal species, and so it is with LSD. The LD50 for the mouse amounts to 50-60 mg/kg i.v. (that is, 50 to 60 thousandths of a gram of LSD per kilogram of animal weight upon injection of an LSD solution into the veins). In the rat the LDso drops to 16.5 mg/kg, and in rabbits to 0.3 mg/kg. One elephant given 0.297 g of LSD died after a few minutes. The weight of this animal was determined to be 5,000 kg, which corresponds to a lethal dose of 0.06 mg/kg (0.06 thousandths of a gram per kilogram of body weight). Because this involves only a single case, this value cannot be generalized, but we can at least deduce from it that the largest land animal reacts proportionally very sensitively to LSD, since the lethal dose in elephants must be some 1,000 times lower than in the mouse. Most animals die from a lethal dose of LSD by respiratory arrest.
The minute doses that cause death in animal experiments may give the impression that LSD is a very toxic substance. However, if one compares the lethal dose in animals with the effective dose in human beings, which is 0.0003-0.001 mg/kg (0.0003 to 0.001 thousandths of a gram per kilogram of body weight), this shows an extraordinarily low toxicity for LSD. Only a 300- to 600-fold overdose of LSD, compared to the lethal dose in rabbits, or fully a 50,000- to 100,000fold overdose, in comparison to the toxicity in the mouse, would have fatal results in human beings. These comparisons of relative toxicity are, to be sure, only understandable as estimates of orders of magnitude, for the determination of the therapeutic index (that is, the ratio between the effective and the lethal dose) is only meaningful within a given species. Such a procedure is not possible in this case because the lethal doge of LSD for humans is not known. To my knowledge, there have not as yet occurred any casualties that are a direct consequence of LSD poisoning. Numerous episodes of fatal consequences attributed to LSD ingestion have indeed been recorded, but these were accidents, even suicides, that may be attributed to the mentally disoriented condition of LSD intoxication. The danger of LSD lies not in its toxicity, but rather in the unpredictability of its psychic effects.
