Colorado wants to study medical marijuana. Federal law is making it tough.

Colorado plans to begin rewarding $9 million in grants for medical marijuana research early in 2015, but, according to the Denver Post, there’s a lot of uncertainty about who will be able to accept the funding.

As with many issues dealing with marijuana, the problem goes back to a disconnect between state and federal marijuana laws. Under the federal government’s classification system , marijuana is still in the most restrictive category, known as schedule 1. Under Colorado law, pot is legal even for personal use.

The divergence in legality causes a lot of complications. With these research grants in particular, the question is whether Colorado’s university-based researchers, who work for institutions that get a lot of federal funding, will be able to accept grants. The big worry for universities — and the review boards that approve studies — is that allowing a study on a federally illegal substance, particularly without federal approval, will cause them to lose millions in federal funds.

Given the federal government’s previous interference in states’ medical marijuana laws, the fear isn’t unfounded. Earlier this year, the Boston Globe reported that the Drug Enforcement Administration (DEA) told several Massachusetts doctors that they either need to drop their involvement with state-legal medical marijuana facilities or risk losing their licenses to prescribe certain drugs. Since doctors’ livelihoods can depend on prescribing, for instance, prescription painkillers regulated by the DEA, the threat essentially forced doctors to choose between working as full doctors or helping set up medical marijuana facilities.

The one way researchers in Colorado may be able to avoid similar hurdles is by getting a license from the DEA for handling schedule 1 drugs for research purposes. But that process could take months or more, depending on how the application process goes.

In many ways, this speaks to one of the big difficulties of marijuana legalization advocates: many of them want to get marijuana’s federal classification changed, but doing so requires research that’s very difficult to conduct under the drug’s current classification. To prove that marijuana can be a schedule 2, 3, 4, or 5 substance, researchers will likely need to show pot has medical value in a large-scale, clinical trial. But as Colorado tries to fund those kinds of studies, the federal government’s own rules are standing in the way.

To learn more about the federal government’s classification of marijuana, read the full explainer, the marijuana legalization card stack, and watch the short video below: