Crackdown on marijuana in California
25 September 2012 Last updated at 20:58 BST
California legalised medical marijuana in 1996, with sixteen other states following suit, but use of the drug remains illegal under federal law.
But the government now says that the recreational use of marihuana has spiralled out of control and dozens of medical marijuana dispensaries in California have been ordered to close, as a federal crackdown looms.
Tom Esslemont reports.