Two American states - Washington and Colorado - have decided to relax their drug laws, effectively meaning that possession of small amounts of marijuana will be decriminalised.
There will be some conflict with federal law, but the votes in November marked a shift in attitudes.
Richard Gil Kerlikowske, director of the Office of the National Drug Control Policy in Washington, told the Today programme's James Naughtie that "there has been this continual shift in attitude" towards the use of marijuana.
"What has been lacking is the information needed for the American public to make these sort of decisions," he added.
"We need to make sure people realise the serious health issues around cannabis."
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