A NEW STUDY in the journal Neurology is being hailed as unassailable proof that marijuana is a valuable medicine. It is a sad commentary on the state of modern medicine -- and US drug policy -- that we still need "proof" of something that medicine has known for 5,000 years.

The study, from the University of California at San Francisco, found smoked marijuana to be effective at relieving the extreme pain of a debilitating condition known as peripheral neuropathy. It was a study of HIV patients, but a similar type of pain caused by damage to nerves afflicts people with many other illnesses including diabetes and multiple sclerosis. Neuropathic pain is notoriously resistant to treatment with conventional pain drugs. Even powerful and addictive narcotics like morphine and OxyContin often provide little relief. This study leaves no doubt that marijuana can safely ease this type of pain.

As all marijuana research in the United States must be, the new study was conducted with government-supplied marijuana of notoriously poor quality. So it probably underestimated the potential benefit.

This is all good news, but it should not be news at all. In the 40-odd years I have been studying the medicinal uses of marijuana, I have learned that the recorded history of this medicine goes back to ancient times and that in the 19th century it became a well-established Western medicine whose versatility and safety were unquestioned. From 1840 to 1900, American and European medical journals published over 100 papers on the therapeutic uses of marijuana, also known as cannabis.

Of course, our knowledge has advanced greatly over the years. Scientists have identified over 60 unique constituents in marijuana, called cannabinoids, and we have learned much about how they work. We have also learned that our own bodies produce similar chemicals, called endocannabinoids.

The mountain of accumulated anecdotal evidence that pointed the way to the present and other clinical studies also strongly suggests there are a number of other devastating disorders and symptoms for which marijuana has been used for centuries; they deserve the same kind of careful, methodologically sound research. While few such studies have so far been completed, all have lent weight to what medicine already knew but had largely forgotten or ignored: Marijuana is effective at relieving nausea and vomiting, spasticity, appetite loss, certain types of pain, and other debilitating symptoms. And it is extraordinarily safe -- safer than most medicines prescribed every day. If marijuana were a new discovery rather than a well-known substance carrying cultural and political baggage, it would be hailed as a wonder drug.

The pharmaceutical industry is scrambling to isolate cannabinoids and synthesize analogs, and to package them in non-smokable forms. In time, companies will almost certainly come up with products and delivery systems that are more useful and less expensive than herbal marijuana. However, the analogs they have produced so far are more expensive than herbal marijuana, and none has shown any improvement over the plant nature gave us to take orally or to smoke.

We live in an antismoking environment. But as a method of delivering certain medicinal compounds, smoking marijuana has some real advantages: The effect is almost instantaneous, allowing the patient, who after all is the best judge, to fine-tune his or her dose to get the needed relief without intoxication. Smoked marijuana has never been demonstrated to have serious pulmonary consequences, but in any case the technology to inhale these cannabinoids without smoking marijuana already exists as vaporizers that allow for smoke-free inhalation.

Hopefully the UCSF study will add to the pressure on the US government to rethink its irrational ban on the medicinal use of marijuana -- and its destructive attacks on patients and caregivers in states that have chosen to allow such use. Rather than admit they have been mistaken all these years, federal officials can cite "important new data" and start revamping outdated and destructive policies. The new Congress could go far in establishing its bona fides as both reasonable and compassionate by immediately moving on this issue.

Such legislation would bring much-needed relief to millions of Americans suffering from cancer, AIDS, multiple sclerosis, arthritis, and other debilitating illnesses.

Lester Grinspoon, an emeritus professor of psychiatry at Harvard Medical School, is the coauthor of "Marijuana, the Forbidden Medicine."

© Copyright 2007 Globe Newspaper Company.