Voters approved the measure 53.6 percent to 46.4 percent with 96 percent of precincts reporting early Wednesday, according to unofficial results.

The vote means the drug will become legal for use on Dec. 15, and marijuana shops can open in 2018. It will pose an immediate challenge for the slow-moving state bureaucracy, which will need to quickly craft new laws and regulations to oversee what could soon be a billion-dollar business.

Massachusetts voters on Tuesday legalized marijuana for recreational use, sweeping away more than a century of prohibition and opening the door to a massive new industry.

The passage of Question 4 came despite opposition from Governor Charlie Baker, Mayor Martin J. Walsh, and Cardinal Sean P. O’Malley who argued it would be a mistake to legalize a new drug while the state battles a scourge of opioid abuse and who said legalization would result in danger to public health and safety.

Voters in four states and the District of Columbia have already legalized marijuana, despite the drug remaining banned under federal law. Massachusetts was one of five states considering legalization Tuesday. California voters approved legalization. Arizona voters rejected it, and the outcome in Maine remained too close to call as of early Wednesday.


“Massachusetts has taken an historic step forward by ending the failed policy of marijuana prohibition,” said Mason Tvert of the Washington-based Marijuana Policy Project, which helped back the effort. “Voters chose to control marijuana rather than to continue forcing it into the underground market. Hopefully, Massachusetts will establish a system that can serve as an example for neighboring states, and others around the country.”

Over the course of the campaign advocates argued the measure would end an antiquated system that ensnared otherwise law-abiding citizens.

They insisted legalization would divert money from criminal syndicates to companies operating on the up and up, and would improve the health and safety of children by moving marijuana sales from the street to licensed stores that check IDs.


Those claims will be put to the test.

Some parts of life in Massachusetts are unlikely to change after Tuesday’s vote. Marijuana consumption remains banned in public places, and smoking it will still be prohibited anywhere tobacco smoking is forbidden. Landlords will be empowered to keep their tenants from smoking a joint at home.

But as soon as next month, a legal gray zone will settle over the state. The measure will allow the possession, use, and purchase of 1 ounce or less of marijuana for adults 21 and older starting on Dec. 15. But there’s no mechanism for buying marijuana for recreational use legally until Jan. 1, 2018, when retail shops can open for business. And marijuana remains illegal under federal law, adding complexities for the many Massachusetts organizations that receive federal funds.

And the new law sets up a cascade of tough decisions for officials across the state, who will have to answer myriad questions.

Among them: Is the new tax on marijuana sales — 3.75 percent in addition to the 6.25 percent sales tax — high enough to pay for enforcement of the law and regulation of the new industry? (Towns and cities will be able to add an additional 2 percent tax to local marijuana sales, if they choose.)

How will police measure drugged driving? State law doesn’t have a marijuana impairment standard like it does for alcohol — 0.08 or greater blood alcohol concentration.


How should government help keep the drug away from children and ensure marijuana isn’t more accessible in high school parking lots and on college quads?

And how much regulation will lawmakers be able to enact before the industry — perhaps like alcohol and tobacco before it — becomes a powerful lobbying force?

State Senator Jason M. Lewis, a legalization opponent and an authority on the industry, said he fully accepts the will of the voters and that state officials “will move forward expeditously to implement the new law.”

But the Winchester Democrat said there are many important details that will be have to addresed by the Legislature and executive branch. And they will have to seek the views of public health experts, law enforcement, town, city and federal officials, the industry, and other people with a stake in the outcome.

“This work will be very complicated and time-consuming,” he said.

The voter-approved law creates a Cannabis Control Commission, an oversight body for the new industry. The three-member group will be appointed by state Treasurer Deborah B. Goldberg and is tasked with setting standards for everything from marijuana advertising to edibles, the marijuana-infused products like brownies that have proliferated in legalization states.

The commission will have also have to address other thorny issues. The law allows people to legally grow up to 12 marijuana plants per household — a significant amount. How will they keep that product from being diverted to the black market?


Municipal leaders must also begin to figure out how to deal with the new industry. They can limit, but not ban, retail stores, cultivation facilities, and marijuana manufacturers. Town or city leadership can call a referendum, however, and voters can decide whether to completely prohibit recreational marijuana businesses.

The win follows pro-marijuana victories in the past two presidential election years.

In 2008, Massachusetts voters approved a ballot measure that replaced criminal penalties for the possession of one ounce or less of weed with a system of civil penalties. That law is usually described as decriminalization.

In 2012, Massachusetts voters approved an initiative making marijuana legal for medical use.

Cristela Guerra, Stephanie Ebbert, and Matt Rocheleau of the Globe staff contributed to this report. Joshua Miller can be reached at joshua.miller@globe.com.