Colorado's marijuana retailers have already made more than $750 million in sales halfway through 2017, a 25.7 percent increase compared to the first half of 2016.

More than $531 million of those sales were for recreational marijuana, and the rest, nearly $220 million, were for medical marijuana, according to an analysis by The Cannabist.

So far, the state has made nearly $116 million in tax revenue and licensing fees through cumulative sales made through June.

However, annual growth rates are expected to slow down for Colorado's marijuana industry.

"What you're seeing in Colorado is similar to other industries, we're starting to see lower double-digit growth rates, rather than the triple-digit growth rates," Bethany Gomez, director of research for cannabis market research firm Brightfield Group said. "That time of massive growth expansion in Colorado, I think, is over."

Colorado's marijuana shops expect to make $131.65 million in total sales for the month of June, after a peak of $131.69 million in March. Despite the small drop off, that will extend the streak of $100 million in monthly sales to 13 months.

Colorado became the first place anywhere in the world to allow legal marijuana sales to anybody over 21 for any purpose in January 2014.

Marijuana does remain illegal at the federal level, and the industry has been waiting for possible changes to federal law. But Attorney General Jeff Sessions has been vocal in his support of the war on drugs, and has made it clear marijuana will remain illegal federally.

Colorado Gov. John Hickenlooper was joined in April by the governors of Alaska, Oregon and Washington, which have all have legalized recreational marijuana, in a letter to Sessions and Treasury Department Secretary Steve Mnuchin urging them to "engage with us before embarking on any changes to regulatory and enforcement systems."

Hickenlooper and Sessions have also met in Washington to discuss legalization in Colorado.

"He has higher priorities," Hickenlooper told Politico earlier this month. "Marijuana's not the same threat to this country as heroin, methamphetamine, cocaine – and he recognizes he has limited resources. He said, 'Listen, we're not going to come in and shut everything down.' We have not seen any crackdown. He really said he didn't plan on having a crackdown."