City councillors in Washington voted unanimously on Tuesday to allow the US capital to join 14 states in allowing medical marijuana to be used to treat certain chronically ill patients.

Under the new law, which has to be signed by Mayor Adrian Fenty and then survive a 30-day period of review by Congress before taking effect, physicians will be able to prescribe to patients suffering from illnesses including HIV/AIDS, , and glaucoma.

Mike Meno of the Marijuana Policy Project (MPP) envisaged no problems with Congress passing Washington's medical marijuana law.

Up to eight licensed dispensaries would be set up for patients to go to get their marijuana, said Meno.

The dispensaries would in turn get their marijuana from licensed growers in the capital, each of which will be allowed to grow up to 95 plants at indoor facilities.

"DC's law doesn't allow personal cultivation," Meno said.

According to MPP, which is the largest marijuana policy reform organization in the United States, ballot initiatives in November in South Dakota and Arizona will ask voters there to choose whether or not to allow medical marijuana in their states.

Another dozen states are mulling similar laws.