Last summer, Kalpna Gupta, professor of medicine at the University of Minnesota, secured $9.5m (£6m; €7.6m) in funding from the National Institutes of Health (NIH) to study whether cannabis can ease the crippling pain experienced by people with sickle cell anemia.

Gupta wanted to focus on sickle cell anemia because more people are developing the disease. “The pain can be intense and increase throughout their life, and then they have crises, which is the worst pain. They need to be hospitalized and they require narcotics again and again,” which can lead to addiction, Gupta says. “We found that cannabinoids are one of the most promising treatments available.”

Yet a year later, in August 2014, Gupta still was unable to launch her study. She encountered strict controls on the study because cannabis is classed as a schedule 1 drug (equivalent to class A in the UK) by the federal Drug Enforcement Administration (DEA). Gupta was told she would need to register with the DEA as a cannabis researcher and make changes to her laboratory, including building a safe to store the marijuana and modifying the clinic where she would carry out the study to ensure that vapors could not seep out. To save time and money, Gupta instead moved her study across the country to the University of California–San Francisco to work with Donald Abrams, a cancer and integrative medicine specialist and professor of clinical medicine, who already had the necessary approvals and had completed five medical cannabis studies since the mid-1990s.

Twenty three states, the District of Columbia, and, most recently, the overseas US territory of Guam have legalized the use of medical marijuana since 1996.1 However, because …