OAKLAND, California (AP) – Armed with a new study that shows smoking marijuana eased pain in some HIV patients, medical marijuana advocates sued the US Government Wednesday over its claim that the drug has no accepted medical benefits.

The lawsuit, filed in US District Court by Americans for Safe Access, accuses the US Department of Health and Human Services of engaging in “arbitrary and unlawful behaviour” that prevents “sick and dying persons from seeking to obtain medicine that could provide them needed, and often lifesaving relief”.

The group wants a judge to force the department and the US Food and Drug Administration to stop giving out information that casts doubt on the efficacy of marijuana in treating various illnesses.

“The FDA position on medical cannabis is incorrect, dishonest and a flagrant violation of laws requiring the Government to base policy on sound science,” Joe Elford, chief counsel for the group, said in a statement.

California is one of 11 states where marijuana use is legal for people with a doctor’s recommendation, but because the US Government does not recognise the drug’s medical benefits, patients can still be arrested and prosecuted by federal authorities.

Last week, researchers from the University of California, San Francisco reported in the journal Neurology that a test involving 50 HIV patients showed that those who smoked pot experienced much less pain than those given placebos.

Americans for Safe Access said in the lawsuit that Health and Human Services has rejected its requests to retract the assertion that cannabis “has no currently accepted medical use in treatment in the United States,” a position the agency has advertised since 2000.

The Department of Health and Human Services did not immediately have a response to the lawsuit.