Buying legal marijuana in Michigan will likely cost about 24% more starting next year, thanks to a tax hike meant to fill potholes. That tax will add to the already 10% excise tax for recreational marijuana and a 6% sales tax. Part of that is a decline in the demand for legal marijuana, as individuals may substitute that legal, taxable product for the illegal, untaxed one.”Hiking taxes threatens Michigan’s legal marijuana market, State Senator Jeff Irwin, D-Ann Arbor, posted on social media. “When Michigan residents approved legal cannabis, we set up a system that was the most successful cannabis market in the nation. The tax hike could cost up to 47,000 jobs, according to Robin Schneider, the director of the Michigan Cannabis Industry of Michigan.