The Massachusetts Medical Society steadfastly opposed the state ballot question passed last fall legalizing marijuana for medical use. One major reason: Not enough research has been conducted to prove the drug’s value to patients.

Dr. Richard Aghababian, the group’s president, sent a letter in October urging the U.S. Drug Enforcement Administration to reclassify marijuana, removing it from the Schedule I list, so it would be easier for researchers to study. The agency responded recently, saying its status among the most tightly controlled illegal drugs “does not preclude scientific research from being conducted using marijuana and its components,” as long as the research receives proper approvals.

“Given this information, it’s time for medical and scientific communities to develop large-scale clinical trials to determine whether marijuana is safe and effective as a medical intervention,” Aghababian wrote Friday on the society’s website. “Such research should identify all the treatment protocols that would apply to a standard pharmaceutical therapy, including indications, contraindications, dosages, length of therapy, side effects, and more.”

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But the people trying to do exactly that work say the Schedule I classification does get in their way.

Aghababian cites the work of a California research center led by Dr. Igor Grant. With state funding and access to the only federally-sanctioned supply of marijuana, that center has conducted a series of small studies have found that marijuana relieved pain in patients with HIV or other conditions and eased muscle stiffness in people with multiple sclerosis.

But much larger trials are necessary. Grant and colleagues wrote last year in the Open Neurology Journal that the “conflict between scientific evidence and political ideology” on this topic is a hindrance:

The classification of marijuana as a Schedule I drug as well as the continuing controversy as to whether or not cannabis is of medical value are obstacles to medical progress in this area. Based on evidence currently available the Schedule I classification is not tenable; it is not accurate that cannabis has no medical value, or that information on safety is lacking. It is true cannabis has some abuse potential, but its profile more closely resembles drugs in Schedule III (where codeine and dronabinol are listed).

Grant told me last fall that state funding for his center’s work had dried up. Others with private funding for marijuana research have not been able to secure access to the federal supply of the drug.

A proposal by the Multidisciplinary Association for Psychedelic Studies , led by Rick Doblin of Belmont, to research the effects of marijuana in veterans with post-traumatic stress disorder was rejected once by federal reviewers who said the study as proposed was not scientifically sound. The group is trying again.

Doblin said in an e-mail Friday that the medical society had missed the point. The real obstacle to research is not necessarily marijuana’s Schedule I classification but the restricted access—he called it a monopoly by the National Institute on Drug Abuse—to the federal drug supply.

His group has been working for 12 years with a University of Massachusetts professor to try to establish another facility in which to grow marijuana in the controlled setting that research requires. The DEA denied the professor’s application for a facility license in 2009, a decision he is appealing in federal court.

I asked Rick Gulla, spokesman for the state medical society for clarification on whether the group would follow-up on the DEA’s response.

“The letter satisfies our concern,” Gulla said. “We still must recognize that marijuana has a potential for abuse and is prohibited under federal law.”