Why were psychedelics banned in the 1960s and 1970s, and what is the 1971 UN convention?

Psychedelics were banned in the 1960s and 1970s because they spread quickly outside the laboratory and governments decided to control them. During the 1960s such drugs became widely available, and authorities opposed this for several reasons, arguing that, along with health harms, drug use led to lowered moral standards. LSD became linked with the hippie counterculture, and it came to be seen as a cultural threat to American values and the Vietnam War effort. In the United States, possession of LSD was made illegal in October 1968, and in 1970 it was classified as a Schedule I drug, illegal even for medical use.

The ban was then written into international law. The 1961 Single Convention on Narcotic Drugs covered only drugs with cannabis, coca and opium-like effects, so it did not reach the many newly discovered psychotropic drugs. A new treaty, the Convention on Psychotropic Substances, was signed in Vienna on 21 February 1971. It lists LSD and natural psychedelics such as certain tryptamines in its strictest schedule, for drugs claimed to create a serious risk to public health and whose therapeutic value is not currently acknowledged.

Two details matter. First, the treaty is not self-implementing: each country must pass its own laws for punishments and restrictions. Second, its stated aim is to limit use to scientific and medical purposes, yet in practice the Schedule I listings made research difficult.

The people in the story were not all bystanders. Harvard psychologists Timothy Leary and Richard Alpert, who had been studying LSD and psilocybin, were fired from the university in 1963, and in 1965 Sandoz stopped distributing LSD. By the early 1970s, scientific study of psychedelics had been effectively halted across much of the world. Whether the controls were a sensible response or an overreaction is still argued.