Detroit — Marijuana became legal at the stroke of midnight Thursday in Michigan, making it the first state in the Midwest to end the controlled substance's prohibition.

A decade after voters approved medical marijuana, the Great Lakes state is the 10th in the union to legalize recreational cannabis use, marking a dramatic change in sentiment, an end to its criminalization and the potential for a multi-million-dollar industry.

"It's a huge accomplishment and a major milestone, not just for Michigan, but for the country," said Josh Hovey, spokesman for the Coalition to Regulate Marijuana Like Alcohol that campaigned for legalization. "For some people, this is a lifetime of work that is being realized. It's a huge accomplishment for those who have been on the ground floor of these legalization efforts for 20, 30 years."

Private events are expected to be held throughout the state Thursday, as longtime and new users celebrate a victory decades in the making after nearly 56 percent of voters approved Proposal 1 on Nov. 6.

"I'm throwing a party on Wednesday night, just because smoking weed while it's illegal has a thrill to it," said Adam Brook, organizer of the annual Ann Arbor Hash Bash. "It's the last night of prohibition."

Meanwhile, opponents to legalization are concerned about what will come over the next few weeks and months as Michigan makes the transition.

"Michigan just isn't really ready for this," said Scott Greenlee, spokesman for Healthy and Productive Michigan, an organization that opposed legalization. "This proposal has a lot of problem with it and a lot of ambiguity. Law enforcement, the business community is worried about what will happen because we are not prepared for this in any way shape or form."

Detroit Police Chief James Craig said at a press conference Wednesday his force is "prepared to address (the law) when it goes into effect."

Anyone over the age of 21 can be in possession of up to 2.5 ounces of marijuana, about 160 joints of 0.5 grams each. It still is illegal to use on federal property, at schools including public universities, and in public.

"You could probably argue it's any place that is publicly accessible," said Barton Morris, founder of the Royal Oak-based Cannabis Legal Group. "Its where anybody can see, even private property so long as it's in-sight. If you're on your front porch, that's not permissible."

A household can grow up to 12 plants out of public sight and have up to 10 ounces, though anything more than 2.5 ounces must be secured.

It is illegal to sell marijuana without a license, though 2.5 ounces can be transferred to a person over 21 at no cost. Michigan's Licensing and Regulatory Affairs Department has a year before it must accept applications from growers, processors and procurement centers. Municipalities can opt out; several already have.

LARA also now has authorization to provide temporary and permanent social-use clubs for the creation of commercial spaces where people can recreationally use it.

It still is illegal to drive while under the influence of marijuana. A first offense is a misdemeanor that carries up to 93 days and a fine of $1,000. It may be accompanied by a license suspension of up to 30 days or five months for a restricted license.

The second offense carries a penalty up to a year. A third offense is a felony with a minimum of 30 days in jail and up to five years. Offenses include driving while under the influence of alcohol and other controlled substances.

Craig said officers who suspect someone is driving while under the influence will need to obtain a search warrant for a blood test.

"It’s not like alcohol where you can smell a strong odor of alcohol," he said. "It’s not different than what we’ve done in the past."

Detroit police issued a framework to all officers on how to enforce the law. Craig said a full training directive will be issued over the next month and that police will continue to respond to complaints and investigate them as usual.

"This isn’t final," Craig said of the framework. "There are issues we're still trying to work through like many other agencies across the state."

bnoble@detroitnews.com

Detroit News Staff Writer Sarah Rahal contributed.