A NEW STUDY in the journal Neurology is being hailedas unassailable proof that marijuana is a valuable medicine. It is asad commentary on the state of modern medicine -- and US drug policy --that we still need "proof" of something that medicine has known for5,000 years.

The study, from the University of California atSan Francisco, found smoked marijuana to be effective at relieving theextreme pain of a debilitating condition known as peripheralneuropathy. It was a study of HIV patients, but a similar type of paincaused by damage to nerves afflicts people with many other illnessesincluding diabetes and multiple sclerosis. Neuropathic pain isnotoriously resistant to treatment with conventional pain drugs. Evenpowerful and addictive narcotics like morphine and OxyContin oftenprovide little relief. This study leaves no doubt that marijuana cansafely ease this type of pain.

As all marijuana research in theUnited States must be, the new study was conducted withgovernment-supplied marijuana of notoriously poor quality. So itprobably underestimated the potential benefit.

This is all goodnews, but it should not be news at all. In the 40-odd years I have beenstudying the medicinal uses of marijuana, I have learned that therecorded history of this medicine goes back to ancient times and thatin the 19th century it became a well-established Western medicine whoseversatility and safety were unquestioned. From 1840 to 1900, Americanand European medical journals published over 100 papers on thetherapeutic uses of marijuana, also known as cannabis.

Of course,our knowledge has advanced greatly over the years. Scientists haveidentified over 60 unique constituents in marijuana, calledcannabinoids, and we have learned much about how they work. We havealso learned that our own bodies produce similar chemicals, calledendocannabinoids.

The mountain of accumulated anecdotal evidencethat pointed the way to the present and other clinical studies alsostrongly suggests there are a number of other devastating disorders andsymptoms for which marijuana has been used for centuries; they deservethe same kind of careful, methodologically sound research. While fewsuch studies have so far been completed, all have lent weight to whatmedicine already knew but had largely forgotten or ignored: Marijuanais effective at relieving nausea and vomiting, spasticity, appetiteloss, certain types of pain, and other debilitating symptoms. And it isextraordinarily safe -- safer than most medicines prescribed every day.If marijuana were a new discovery rather than a well-known substancecarrying cultural and political baggage, it would be hailed as a wonderdrug.

The pharmaceutical industry is scrambling to isolatecannabinoids and synthesize analogs, and to package them innon-smokable forms. In time, companies will almost certainly come upwith products and delivery systems that are more useful and lessexpensive than herbal marijuana. However, the analogs they haveproduced so far are more expensive than herbal marijuana, and none hasshown any improvement over the plant nature gave us to take orally orto smoke.

We live in an antismoking environment. But as a methodof delivering certain medicinal compounds, smoking marijuana has somereal advantages: The effect is almost instantaneous, allowing thepatient, who after all is the best judge, to fine-tune his or her doseto get the needed relief without intoxication. Smoked marijuana hasnever been demonstrated to have serious pulmonary consequences, but inany case the technology to inhale these cannabinoids without smokingmarijuana already exists as vaporizers that allow for smoke-freeinhalation.

Hopefully the UCSF study will add to the pressure onthe US government to rethink its irrational ban on the medicinal use ofmarijuana -- and its destructive attacks on patients and caregivers instates that have chosen to allow such use. Rather than admit they havebeen mistaken all these years, federal officials can cite "importantnew data" and start revamping outdated and destructive policies. Thenew Congress could go far in establishing its bona fides as bothreasonable and compassionate by immediately moving on this issue.

Suchlegislation would bring much-needed relief to millions of Americanssuffering from cancer, AIDS, multiple sclerosis, arthritis, and otherdebilitating illnesses.

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