Project MKUltra

In the 1950s and '60s, the Central Intelligence Agency conducted human experiments on the application of drugs, hypnosis, sensory deprivation, and isolation toward mind control and information extraction. You can read more about the program here:
Project MKUltra

Much of the research centered around using psychedelic drugs to influence thought in subjects, mainly using the gold standard of psychedelics, lysergic acid diethylamide (LSD). To really understand why the CIA was so interested in this line of research, it's important to consider the context of MKUltra.

The enthusiasm bubble that quickly built after the discovery of LSD in 1943 reached a crescendo at the start of the 1960s. Like penicillin, LSD was uncovered by accident, and like penicillin it seemed to be a wonder drug during its initial clinical trials. Study after peer-reviewed study showed it to be effective at treating addiction, alcoholism, obsessive-compulsive personality, and post-traumatic stress disorder. LSD was the first truly effective antidepressant to enter the arsenal of psychiatrists, and more recent research has shown it to be capable of easing cluster headaches and end-of-life anxiety in terminally ill patients. Naturally, the CIA wanted to find out if this penicillin for the soul could be weaponized.

The concept of weaponized psychedelic hallucinogens seems terrifying enough to me, but in addition to the basic uncouthness of the idea the CIA insisted on testing the effects of altered-consciousness interrogation on uninformed, unconsenting participants. There's substantial evidence that Ted Kaczynski was a subject in one of the experiments, and even if this had no influence on his later stint as the Unabomber, surely there was much unnecessary suffering rendered on the American public by the trials. Like the enhanced interrogation program of the Bush years, this is hopefully a chapter of history that the American intelligence community would rather not repeat.

Also it turns out that LSD doesn't work for mind control. Thanks CIA, lesson learned.