New research gives more ammunition to those hoping to change federal marijuana policy.

Ever since California and other states began passing medical marijuana laws in 1996, the federal government has claimed that -- as a 2003 White House press release put it -- "research has not demonstrated that smoked marijuana is safe and effective medicine." A new study, just published in the journal Neurology, definitively refutes that claim and underlines the urgent need for the federal government to change its prohibitionist policies.

The study, conducted by Dr. Donald Abrams of the University of California at San Francisco, found marijuana to be safe and effective at treating peripheral neuropathy, which causes great suffering to HIV/AIDS patients. This type of extreme pain, which is caused by damage to the nerves, can make patients feel like their feet and hands are on fire, or being stabbed with a knife. Similar pain is seen in a number of other illnesses, including multiple sclerosis and diabetes, and cannot be treated effectively with conventional pain medications. Standard pain medicines -- even addictive, dangerous narcotics -- have little effect on this type of pain.

Marijuana doesn't cure neuropathy, but in the UCSF study marijuana was clearly shown to give relief. In this randomized, double-blind, placebo-controlled trial (the design that's considered the "gold standard" of medical research), a majority of patients had a greater than 30 percent reduction in pain after smoking marijuana. For many, that level of relief means having a bearable quality of life.

This result is all the more remarkable because researchers like Abrams are only allowed to test government-supplied marijuana, which is of notoriously poor quality. There's every reason to believe the results would be even better if scientists were permitted to study a better-quality product.

Abrams' study is only the latest in a growing mountain of research showing that medical marijuana can provide real -- and potentially even life-saving -- benefits. In a study published last year of patients being treated for the hepatitis C virus (HCV), those who used marijuana to curb the nausea and other noxious side effects of anti-HCV drugs were significantly more likely to complete their treatment. As a result, the marijuana-using patients were three times more likely to clear the deadly virus from their bodies -- in other words, to be cured -- than those not using marijuana.

Clearly, the White House and its drug czar, John Walters, should abandon their rigid, unscientific rejection of medical marijuana and start reshaping federal policy to match medical reality.

Unfortunately, this is unlikely; what's more likely is that the Bush administration will ignore the scientific data during its last two years in power, just as it has for the past six years.

That puts the ball in Congress's court. There are a number of actions Congress can take to put federal medical marijuana policy on a path toward sanity.

The first, and simplest, is to prohibit the Drug Enforcement Administration from spending money to raid and arrest medical marijuana patients and caregivers in the 11 states where the medical use of marijuana is legal under state law. This taxpayer-friendly act would remove the cloud of fear that now hangs over tens of thousands of desperately ill Americans and those who care for them.

But that should be just the beginning. Everything about federal medical marijuana policy should be reconsidered. That includes the arbitrary rules that needlessly hamper research, as well as the absurd law that classifies cocaine and methamphetamine as having more medical value than marijuana, which is grouped with heroin and LSD as having "no currently accepted medical use."

The guiding principle must be to handle medical marijuana as science, common sense, and simple human decency dictate. Recent research leaves no doubt that our government's war on the sick and dying must end immediately.

Rob Kampia is executive director of the Marijuana Policy Project in Washington, DC.