Why it is probably too soon to assess the public health effects of legalisation of recreational cannabis use in the USA.

The citizens of four US states-Alaska, Colorado, Oregon, and Washington-have voted to legalise the sale of cannabis to adults for recreational purposes, and more states look likely to follow. Experience with alcohol and tobacco suggests that a for-profit legal cannabis industry will increase use by making cannabis more socially acceptable to use, making it more readily available at a cheaper price, and increasing the number of users and frequency of their use. We argue that it is too early to see the full effects of legalised cannabis policies on use and harm because several factors could delay the full commercialisation of a legal cannabis industry. These factors include restrictions on various licensed producers and sellers, and legal conflicts between Federal and State laws that might provide a brake on the speed and scale of commercialisation in states that have legalised cannabis. Any increases in cannabis use and harm could be minimised if governments introduced public health policies that limited the promotional activities of a legal cannabis industry, restricted cannabis availability to adults, and maintained cannabis prices at a substantial fraction of the black market price. So far, no states have chosen to implement these policies.