San Francisco ? Smoking marijuana eased HIV-related pain in some patients in a small study that nevertheless represented one of the few rigorous attempts to find out if the drug has medicinal benefits.

The Bush administration’s Office of National Drug Control Policy quickly sought to shoot holes in the experiment.

The study, conducted at San Francisco General Hospital from 2003 to 2005 and published Monday in the journal Neurology, involved 50 patients suffering from HIV-related foot pain known as peripheral neuropathy. There are no drugs specifically approved to treat that kind of pain.

Three times daily for nearly a week, the patients smoked marijuana cigarettes machine-rolled at the National Institute of Drug Abuse, the only legal source for the drug recognized by the federal government.

Half the patients received marijuana, while the other 25 received placebo cigarettes that lacked the drug’s active ingredient, tetrahydrocannabinol. Scientists said the study was the first one published that used a comparison group, which is generally considered the gold standard for scientific research.

Thirteen patients who received marijuana told doctors their pain eased by at least a third after smoking pot, while only six of those smoking placebos said likewise.

The marijuana smokers reported an average pain reduction of 34 percent, double the drop reported by the placebo smokers as measured with a widely accepted pain scale.

Many critics of smoked marijuana agree THC has promise as a painkiller, but they argue the smoke itself is harmful.