The US government has approved new growers of research cannabis, ending a 53-year monopoly on cannabis cultivation.

Since 1968, all researchers have been required to use cannabis grown at the University of Mississippi under a contract with the National Institute on Drug Abuse.

Dr Sue Sisley: at the forefront of the campaign to end the monopoly

Campaigners have long complained the low quality of the cannabis produced has made it impossible for researchers to assess its medical potential compared to the high-quality product sold in dispensaries in states where medicinal use is legal.

Scottsdale Research Institute (SRI) is one of several companies to be told by the Drug Enforcement Administration (DEA) that its application to grow cannabis for research has been preliminarily approved.

SRI and its principal Dr Sue Sisley have been at the forefront of dismantling the monopoly, launching multiple successful lawsuits against the DEA in the last two years.