Researchers surveyed almost 600,000 adults between 2002 and 2104
More and more Americans are getting high smoking marijuana, according to the results of a study covering a period of 12 years between 2002 and 2014.
Reuters reports that almost 600,000 people were surveyed in the research published by The Lancet Psychiatry.
Recreational marijuana is currently legal in four states in the US: Colorado, Alaska, Oregon and Washington, with a further 24 states allowing its use medicinally.
The number of adults in the US using marijuana daily or nearly every day, more than doubled over the course of the study from 3.9 million to 8.4 million.
The study also notes that changes in the risk perception of the drug started in 2006.
In Colorado alone, legal marijuana sales in 2015 were nearly $1 billion which brought in roughly $135 million in tax revenue which the state has diverted towards school construction among other public projects.
According to Forbes, the US marijuana market will grow to $7.1 billion by the end of 2016. The total 2015 sales of the drug were higher than renowned brands such Oreos and Girl Scout cookies.
A number of states, including Florida, Arkansas and Missouri are due to vote on the use of medicinal marijuana legislation this November and at least five states are looking to legalise recreational use.