The legal marijuana industry could explode by 2020

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An unidentified man sits beneath a California state flag that has been decorated with pot leaves at the San Francisco Patients Cooperative, a medical marijuana dispensary.

The "green rush" is about to get even bigger, according to a new report from Arcview Market Research, a leading publisher of marijuana market research.

Five states will vote to legalize recreational marijuana this November, while medical marijuana is up for consideration in four more states. Should ballot initiatives pass in select key states (California, Arizona, Nevada, Massachusetts, Maine, Montana, and Florida), those markets will account for $2.7 billion in additional marijuana sales in 2018, Arcview reports.

That number grows to nearly $8 billion by 2020.

Arkansas and North Dakota were not included in Arcview's estimates because initiatives there were added too late to the ballots for the research group to develop a full market projection, an Arcview spokesperson tells Business Insider.

Arcview projects the legal marijuana market will hit $20.6 billion in revenue by 2020, up from $5.4 billion in 2015. That's more than what Americans spent on chocolate last year and nearly double what the US porn industry rakes in annually.

In other words, that's an insane amount of weed.

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A worker carries medical marijuana at a growing facility.

"The cannabis industry is one of the fasting growing sectors in the economy and continues to astonish those in and out of the space," Giadha DeCarcer, founder and CEO of marijuana big data company New Frontier, tells Arcview.

Poll data shows support for legalization in Massachusetts, Maine, California, and Nevada, but less so in Arizona, where conservative Governor Doug Ducey opposes an initiative that would make it legal for residents age 21 and over to use and cultivate marijuana.

In California, where medical marijuana has been legal since 1996, over 60% of survey respondents asked about Proposition 64 expressed support, according to Ballotpedia's average of polls. The initiative would allow for an alcohol-style regulation and sale of marijuana.

In spite of all this, Arcview has actually lowered its expectations for the legal marijuana industry since March of this year, down from $22.8 billion to $20.6 billion. The report explains that new market data, plus operational challenges in nascent markets, are responsible for the dip.