Most states sell it only for medical purposes, often broadly defined. But four states—Alaska, Colorado, Oregon and Washington—and the country's capital have gone further, legalising the drug’s recreational use. Legal weed is more expensive than the black market variety, but it is better value: three times more potent, on average, and only about 50% dearer. A slim majority of Americans now favours legalisation, but support varies widely. Whereas in the west the legalisers outnumber the prohibitionists easily, in the north-east opinion is split almost down the middle.

READ MORE: “The right way to do drugs”this week's leader and “Reeferegulatory challenge” our briefing.

Correction: An earlier version of this map incorrectly denoted the legal status of marijuana in a handful of states. This was corrected on February 16th.