An employee collects money while holding packages of marijuana at Top Shelf Cannabis in Bellingham, Washington, on July 8, 2014, the first day of recreational sales in the state. (David Ryder, Getty Images file)

How much will the marijuana industry bring in this year?

ORLANDO, Fla. — Retail marijuana sales in the United States are expected to be $4.5 billion this year, but constant changes in state regulations are creating hurdles for business people trying to make money off pot.

That’s the word coming out of the Marijuana Business Conference & Expo being held in Orlando, Florida, this week.

Chris Walsh, editorial director of Marijuana Business Daily, says marijuana sales doubled in the United States from 2013 to 2015.

Right now, 19 states have legalized medical marijuana. Another four states, as well as the District of Columbia, allow marijuana for both medical and recreational uses.

Walsh estimates 100,000 people are directly and indirectly employed in the industry, and 80 to 90 percent of companies are profitable.

But Walsh says start-up costs are rising.