The LD50 of LSD varies from species to species. Rabbit is the most sensitive species known, with LD50 of 0.3 mg/kg i.v. The LD50 for rats is ten times higher at 16.5 mg/kg i.v. Mice tolerate 46-60 mg/kg i.v. LSD (Passie et al, 2008). An intraperitoneal dose of LSD 5.0 mg/kg reportedly caused death in a rat within 30-45 minutes and was associated with cardiac irregularities and general rigidity of musculature (Sylar et al, 1971). A too high dose of LSD typically causes animals to expire by paralysis, bradycardia, or respiratory failure; these effects probably involve centers in the caudal brain stem.
In an experiment with Macacus rhesus, one animal received 240 ug/kg and the other 140 ug/kg, which are enormous doses of LSD. In terms of a 70 kg person, the animals received 168 and 98 hits of LSD. These doses did not produce an excited behavior in monkeys as small doses do, but instead produced sedation. The monkeys became quiet and more sluggish around the cage, and did not jump about the cage as they did before. The monkeys lived.
Reference
Passie, T., J.H. Halpern, D.O. Stichtenoth, H.M. Emrich and A. Hintzen 2008. The pharmacology of lysergic acid diethylamide: A review. CNS Neurosci. Ther. 14, 295-314.