The federal Drug Enforcement Administration has just issued a helpful reminder to all Americans. In denying a petition to loosen restrictions on cannabis, the agency repeated that the drug has “no currently accepted medical use” in the United States.

This may come as a surprise, given that 25 states already allow doctors to prescribe cannabis to treat maladies from post-traumatic stress disorder to Alzheimer’s disease. Yet the truth is that research has yet to find firm evidence that cannabis can alleviate physical suffering.

That the political push for medicinal cannabis has gone so far ahead of science explains why cannabis is still properly classified as a Schedule I controlled substance. It is also why the Barack Obama administration, in other big cannabis news this week, was right to enable more medical studies of the drug by increasing the supply available to researchers.

Cannabis’ unearned reputation as a therapeutic drug is partly an outgrowth of its contradictory legal status in the US. Federal law forbids the possession, use and sale of cannabis for any reason. States wanting to get around this prohibition have found it most publicly acceptable to allow limited use, and have latched on to claims that “pot” can help to treat various ailments — for example, the nausea caused by chemotherapy, pain and muscle spasms from multiple sclerosis, epilepsy, Crohn’s disease and glaucoma.

Still, the science behind such claims is, at best, preliminary. And too little is known about cannabis’ potential side-effects on bronchial and cardiac health, fetal and teenage brain development and, of course, addiction.

Doctors in states that have legalised medicinal cannabis have essentially been left on their own to figure out how to respond to patient requests. Just this week, the Federation of State Medical Boards issued guidelines, which, in the absence of data on cannabis’ usefulness, are by necessity limited. Doctors are advised to keep accurate records, to avoid prescribing cannabis to people with substance abuse disorders, to “discuss the risks and benefits” and to remind patients not to operate heavy machinery while under the influence. That is sound advice, but applicable to just about ... anything.

Cannabis research studies are properly controlled and monitored by both the DEA and the Food and Drug Administration. But they have also been limited more than necessary by a DEA rule that has authorised only the University of Mississippi to grow cannabis for research purposes. Other universities will now be licensed to grow cannabis, and that is expected greatly to expand the supply available for research.

Cannabis is already widely used as medicine in the US. The more studies that can get under way, the sooner a confused public can learn with some empirical certainty whether its spread is for good or for ill, and the sooner the science can catch up to the politics.