More than a dozen states have followed suit since and several others - the most recent of which is Massachusetts - have approved laws decriminalising the possession of small amounts of the drug.
Now, there are moves afoot in California to go further to fully legalise marijuana.
Evidence of the impact that the approval of medicinal marijuana has had on some areas of California is clear in Oakland.
Across the bay from San Francisco, it has come to be known as Oaksterdam, in a nod to the symbolic global capital of marijuana deregulation, Amsterdam. More...