The Museum of Hoaxes provides an excerpt from the book Elephants on Acid: And Other Bizarre Experiments:
Warren Thomas, Director of the City Zoo, fired a cartridge-syringe containing 297 milligrams of LSD into Tusko the Elephant’s rump. With Thomas were two scientific colleagues from the University of Oklahoma School of Medicine, Louis Jolyon West and Chester M. Pierce.
297 milligrams is a lot of LSD – about 3000 times the level of a typical human dose. In fact, it remains the largest dose of LSD ever given to a living creature. The researchers figured that, if they were going to give an elephant LSD, they better not give him too little.
(via Boing Boing).