BACKGROUND: Cannabis was introduced to the UK as a medical product in the nineteenth century. However, with questions over its safety, efficacy, and possible harms its medical role diminished and by the 1950s it was viewed as a drug of misuse. Nonetheless, scientific and lay knowledge around cannabis expanded from the 1960s and cannabis re-appeared in different therapeutic forms. In re-medicalizing cannabis, science-policy transfer proved important and was enabled by the developing mechanism of expert committees, most notably the Advisory Council on the Misuse of Drugs (ACMD). METHODS: This article draws upon previously unknown archival material on the ACMD held at the National Archives and covers the period 1972-1982. It considers how expert groups were established, their membership, and the evolving discussion over therapeutic cannabis within the broader drug policy debate. RESULTS: Three distinct periods emerged: 1972-1976 with the creation of the Working Group on Cannabis; 1977-1979 when the Working Group focused on potential amendments to the Misuse of Drugs Act and recommended downgrading cannabis from Class B to Class C; 1980-1982 when the Expert Group on the Effects of Cannabis recommended downgrading cannabis and encouraged research into cannabis as a medicine. Sources reveal that driven by drug control imperatives the ACMD stimulated research on cannabis leading to increased research on medical applications. CONCLUSION: Expert advice was critical in the process of re-medicalization. Initially, discourse occurred in the closed expert committees of the ACMD. The drug problem had been framed under the criminal justice system but as the limitations of this were revealed, and there was continuing uncertainty over cannabis' impact, new approaches to cannabis were sought. It was this combination of more relaxed attitudes towards cannabis, research incentives, as well as a developing desire to draw medical needs away from discussion of drug control that was to allow re-medicalization to develop.