Massachusetts voters in 2½ weeks will consider becom­ing the 17th state to ­legalize the use of marijuana for medical purposes. But there is little research showing whether the drug has therapeutic benefits.

That says more about the difficulty of studying an illegal substance than it does about the inherent medical value of the plant.

Opponents of the proposal say medical practice should be defined by rigorous study and drugs vetted by the US Food and Drug Administration, not by popular opinion. Advocates say federal drug policy has thwarted that process. They point to abundant anecdotes and a collection of small studies that found marijuana to be effec­tive in alleviating pain and muscle stiffness in people with chronic conditions.

Ethan Ruby has no doubt that marijuana is medicine. The 37-year-old, who grew up in Southeastern Massachusetts, was struck by a drunk driver in a Manhattan crosswalk 12 years ago. He has no feeling ­below his chest except for persistent pain in his legs.

To cope, Ruby relies on a small dose of marijuana, sometimes several times a day. The drug distracts him from the pain long enough to focus on his business pursuits or to spend good-quality time with his wife and two children, he said. It allowed him to cut his use of prescription narcotic painkillers from daily to occasional.

For some doctors in the state, though, such ­examples are not enough.

“For any other drug, there has got to be testing,” said Dr. Joseph Gravel, chief medical ­officer of the Greater Lawrence Family Health Center and president of the Massachusetts Academy of Family Physicians

The Massachusetts Medical Society opposes the referendum, but sent a letter to the US Drug Enforcement Administration this month urging that marijuana be reclassified to make it easier to ­research.

Use of a ballot question to determine medical practice is worrisome, Gravel said, as is promotion of a drug that is typically smoked. He and others said the more responsible path would be to develop drugs ­derived from components of marijuana, the way morphine is derived from opium.

One drug already on the market, Marinol, uses synthetic tetrahydrocannabinol, or THC, to treat nausea in people undergoing chemotherapy. But doctors interviewed for this ­report said its effect is limited, and researchers suspect that marijuana components interact for greater ­effects than THC alone.

Individual doctors and patient advocacy groups, including the AIDS Action Committee of Massachusetts and the state chapter of the Leukemia and Lymphoma ­Society, have endorsed the ballot question, saying marijuana can help patients and is available now.

There is ample anecdotal evi­dence to support the idea, said Dr. Eric Ruby, Ethan’s ­father and a Taunton pediatrician who has become a vocal advocate for the Massachusetts proposal.

“We haven’t done the studies because [the drug is] illegal,” he said. “Because it’s illegal, we can’t do the studies. That’s not scientific. That’s circular.”

To study marijuana, ­researchers must be licensed by the US Drug Enforcement Admin­istration and get access to marijuana grown at the University of Mississippi, which contracts with the National ­Institute on Drug Abuse to produce the only federally sanctioned supply. That process can prove onerous, if not impossible, acting as a ­deterrent for those who might want to study marijuana’s benefits, some ­researchers said.

In 2000, the University of California created the Center for Medicinal Cannabis ­Research, with $9 million from the state. The state’s blessing and the university’s reputation helped to secure federal ­approvals, said Dr. Igor Grant, the center’s director, who is based in San Diego. In the past decade, he and colleagues have completed the most comprehensive research to date of the effects of marijuana in patients, including studies that were randomized and double-blind, gold standards in research.

Four studies found the drug to be useful in treating pain. Three were in patients with HIV who had pain resulting from damage to their nervous system. Another study found that marijuana reduced muscle stiffness in patients with multiple sclerosis. But the studies were small, each involving dozens of ­patients rather than the hundreds or thousands needed to advance the drug toward federal approval.

“What’s surprised us, actually, was the consistency of the evidence,” Grant said.

The next step would be to pursue large trials and to compare smoked and vaporized marijuana with approved drugs. But Grant’s center has reached the end of its funding, with no more promised from the state.Continued...