Medical research on marijuana probably won't get any easier, experts say, despite a new government policy aimed at boosting the supply of the drug for medical studies.

That means the types of studies that are needed to address the safety and effectiveness of the drug as a medicine could still be a long way off.

Marijuana's legal status as a "Schedule I" drug, which makes it an illegal drug on the federal level, "severely constrains the access and the number and type of people who can do research with cannabis," said Ryan Vandrey, an associate professor of psychiatry and behavioral sciences at The Johns Hopkins University School of Medicine who studies marijuana. "The unfortunate result of that is that we're now in a situation where you have literally millions of people using a drug for which we don't have established safety or efficacy data," Vandrey said. [11 Odd Facts About Marijuana]

On Thursday (Aug. 11), the U.S. Drug Enforcement Administration (DEA) announced that it will allow more universities to apply to grow marijuana intended for use in medical studies, with the hope of providing researchers with a "more varied and robust supply" of medical marijuana, the agency said in a statement. Currently, the University of Mississippi is the only place in the United States that is allowed to grow and supply marijuana for use in research. The DEA said the change was intended to "foster research" on marijuana.

But that same day, the agency denied two petitions from U.S. governors to reclassify the drug into a different category, meaning marijuana remains an illegal substance, like heroin and LSD, subject to the most stringent drug regulation. The agency said it made that decision because there is a lack of evidence showing the effectiveness and safety of the drug for medical purposes.

But marijuana's illegal status makes it very difficult to carry out rigorous studies on the drug — the exact type of studies that are needed to definitively test its merit as medicine.

"Every research protocol we design and want to do has to go through a number of extra regulatory approval before we can do them," Vandrey told Live Science. "The consequence of that is, we have major delays in getting done what we need to get done." The supply of marijuana available for research doesn't change any of that, he added.

Vandrey said it took him a year and a half to get all of the necessary regulatory approvals for a recent medical marijuana study involving 76 people at two research facilities. Larger studies involving more hospital sites — the kind of studies that are generally looked upon as a gold standard for research in testing out any new drug — would be incredibly difficult, he said.

Before a facility can carry out a medical marijuana study, the researchers need to apply for a "Schedule I license," which involves an evaluation for safety and security. Many hospitals wouldn't be able to meet the criteria for a Schedule I license because they don't have the security or infrastructure required for it, Vandrey said.

The new policy allowing more universities to apply to grow marijuana "doesn't change how easy research generally is, because it doesn't change the regulation required for research," Vandrey said.

Dr. Jacci Bainbridge, a clinical pharmacy specialist at the Skaggs School of Pharmacy at the University of Colorado Anschutz in Aurora, who studies medical marijuana, agreed. The new DEA policy "might not make it more feasible to do the research, because there are other regulatory hurdles … that may prevent you from doing the research the way you would want to do it," Bainbridge said.

Bainbridge cited hurdles to marijuana research within university systems, which can exist because many universities receive federal funding. For example, in the studies of marijuana that Bainbridge and her colleagues conduct, they cannot have study participants take the drug on campus, and researchers cannot witness participants taking it. In addition, researchers cannot test the marijuana product themselves in order to know the strain or potency of tetrahydrocannabinol (THC, the main active ingredient in marijuana) or whether it has contaminants, Bainbridge said. The product needs to be sent to an outside lab for testing.

"It's so difficult, because we can't really thoroughly do a good job studying what our patients are actually taking," Bainbridge told Live Science. "You feel like you just can't do those great, high-quality trials" that researchers do with other drugs, she said. [Marijuana Could Treat These 5 Conditions]

The new DEA policy would have been helpful if it had produced a type of marijuana product that's not currently available to researchers to study, like a marijuana patch, Vandrey said. But it's not clear if that would happen as a result of the changes.

It's also not clear if other universities will actually apply to grow medical marijuana under the new policy, because the cost to set up a facility and maintain security would be extraordinary, Vandrey said. Last year, the University of Colorado voted down the idea of growing its own medical marijuana, mainly because of the cost, Bainbridge said.

The DEA said it is working on other measures to support marijuana research, such as building an online application system for researchers to apply for the registrations needed to study Schedule I drugs. Last year, the DEA also said it would waive certain regulatory requirements for studies involving cannabidiol (CBD), a chemical in marijuana that does not have mind-altering effects.

Original article on Live Science.