The use of cannabis for medicinal purposes is becoming increasingly commonplace in the US, with 25 states now allowing the practice, while a further four have gone a step further and legalized recreational weed smoking. However, despite the fact that more and more people are now being prescribed the drug, some scientists worry that the federal government is placing too many obstacles in the way of meaningful research into the effects of cannabis, meaning no one really knows the full extent of its benefits and dangers.

In a letter published recently in Science, University of New Mexico economics assistant professor Sarah Stith and psychology assistant professor Jacob Vigil lamented that “to conduct research on cannabis, scientists must submit to a lengthy and arduous application process, often lasting for years.” This, they say, has prevented most meaningful marijuana studies from getting off the ground.

Part of the reason for this mess is that, while in many areas of the US cannabis has now been made legal at state level, it remains banned on a federal level, and is classified as a Schedule 1 substance. As such, marijuana research “requires permission from multiple governmental agencies, including some with expressly stated opposition to any therapeutic uses, such as the Drug Enforcement Agency [DEA].”

In a statement, Stith and Vigil explain that the DEA has a history of deliberately stalling and impeding cannabis research, yet surprisingly, they do not identify this as the biggest obstacle to scientists working with weed. Instead, they claim that the single biggest factor getting in the way of researchers is that they have to obtain their marijuana from the National Institute of Drug Abuse (NIDA), which provides weed with a maximum THC concentration of 12.4 percent. In contrast, most states where the drug is legal do not have potency limits on medical marijuana, which can contain up to 35 percent THC in extreme cases.

Therefore, while the average strength of medical marijuana in Colorado is 18.7 percent, the only two studies on the drug conducted in 2015 used cannabis that contained just 3.5 and 7 percent THC.

Because of this, the authors of the letter explain that “the scarce research the US government has approved thus offers little insight into the effects actually experienced by patients and recreational users,” adding that “many severely ill patients may suffer unnecessarily because no one knows the true risks and benefits of consuming cannabis.”