Defenders of Hawaii’s medical marijuana law were startled this week by a late effort to sharply limit uses of marijuana to reduce severe pain. The proposal carries an assumption that either doctors or patients are being less than candid about whether the pain actually exists. This may be. But the onus should be on Sen. Josh Green, who proposed the last-minute change, to provide evidence of such shenanigans before such changes become law.

Green, a Big Island emergency room physician and chairman of the Senate Health Committee, injected the proposal in a House-Senate conference this week in a bill to launch a medical marijuana dispensary as a pilot program.

The senator’s concerns about the program — "pretty hard to wrap my mind around" — are not surprising. Opponents of medical marijuana point out that the number of Hawaii residents issued blue cards by the state Department of Public Safety as legal users has soared from 255 in 2001, the program’s first year, to more than 8,000.

Hawaii’s law, similar to laws in 10 other states, allows cannabis to be used by patients diagnosed as having a debilitating medical condition. That condition includes a variety of ailments, including severe pain, severe nausea and Crohn’s disease, an intestinal condition.

Keith Kamita, deputy director of public safety for law enforcement, says the bulk of residents certified to use medical marijuana are in their 20s and 30s, and most of them cite severe pain as their medical condition. Green proposed that marijuana be accessible only to patients suffering from multiple sclerosis, cancer, HIV/AIDS or glaucoma.

A cautious approach makes sense for a pilot project. As Hawaii gingerly tests the waters of marijuana dispensaries, it should proceed carefully, with clear guidelines for physicans and patients alike. The four diseases enumerated by Green are objectively and physically diagnosable. Not so with cases of pain, which depend on a doctor’s trust of his or her patients.

Dr. Jim Berg, a Big Island physician who the Narcotic Enforcement Division records showed had authorized 2,957 marijuana certificates as of last June, defends the medical use.

In an open letter to Green yesterday, Berg maintained that he has "witnessed the truth of these patients and know it helps them, and that it can be used safely." He suggested that his patients include those who have chronic neck, shoulder, wrist, ankle, knee or back pain from injuries in manual labor jobs.

Matt Rifkin, co-chairman of the Big Island Americans for Safe Access, an advocate of medical marijuana rights, says the limitation proposed by Green could disqualify most the patients who now have blue cards.

Berg says it would effectively disqualify more than 90 percent of currently registered patients.

Green’s concern may be worthy of an investigation into the integrity of the medical marijuana program. But there are no shortcuts. Any proposals to lay the ground rules for such a controversial program deserve a full public vetting before being implemented.