Marijuana is quickly becoming a legal multi-billion-dollar industry in the United States, prompting new research into multiple aspects of the drug, including both use and production.

In fact, the use of medical marijuana is now legal in 29 states and the District of Columbia. And, eight states have passed laws allowing for the legal use of marijuana recreationally. Michigan could become the ninth later this year, where the city of Detroit already allows the sale of marijuana in stores with proper licensing.

“This is obviously an ongoing controversy and there is widespread debate over the use medical marijuana when it comes to the spillover effects of a medical marijuana law adoption,” said Yajuan Li of Texas A&M University.