LSD

LSD — or, as the Second Doctor called it, lysergic acid diethylamide — was an hallucinogenic drug central to the American counter-culture movement of the late 1960s. It was widely available in San Francisco, for instance, during the so-called Summer of Love in 1967. However, a particularly toxic strain of it emerged at that time, threatening and even taking the lives of many of the city's young people.

The Doctor synthesised what he felt was a less dangerous version of LSD and even injected someone with it in order to help solve the mystery of the Colour-Beasts. (PROSE: Wonderland)