In 2014, many states experimented with marijuana laws

This was the first year adults in Colorado and Washington could walk into stores and legally purchase marijuana. Those purchases are part of a growing wave of marijuana legalization and decriminalization in the United States.

Across the country, states have relaxed their drug laws and experimented with new policies that ease penalties for marijuana use or make it available to medical patients.

Where can people use marijuana?

Given the array of different approaches — legalization, decriminalization, medical marijuana, and various combinations of these — any map of marijuana policy is bound to be pretty colorful. One thing these maps clearly show is the dwindling number of states where marijuana remains a serious legal offense and where there are no medical exceptions.

Source: Pew Research Center.

What were the big changes of 2014?

Oregon, Alaska, and Washington, D.C., all voted to follow the lead of Colorado and Washington state, creating a regulated market for buying, growing, and selling marijuana. The D.C. initiative has since been blocked by Congress, but the others are moving ahead.

D.C. did successfully pass a decriminalization law in 2014, which ensures that people caught with small amounts of marijuana will be fined, rather than arrested. Similar laws were passed this year in Maryland, Missouri, and Philadelphia. Also in 2014, New York and Minnesota passed new plans to allow medical marijuana.

Here in Massachusetts, 2014 was notable for its lack of activity. It’s been two years since voters gave their assent to medical marijuana in the Bay State, and as yet there are no active dispensaries. Some states, like Maine, have managed to authorize dispensaries more quickly. Others, like New Jersey, have taken far longer.

Have there been any setbacks?

Such is the momentum behind the movement that no state has been moving to tighten restrictions on marijuana. However, Nebraska and Oklahoma closed the year by filing a lawsuit against their neighbor Colorado, claiming that marijuana from Colorado is spilling over the border.

Since it involves a dispute between states, the suit can go directly to the Supreme Court — so it shouldn’t be long before we know how it affects the legalization movement.

How much has public opinion really shifted?

Quickly and resoundingly. Twenty years ago, just one in five people supported marijuana legalization. Ten years ago, it was one in three. Now, it’s the majority view.

One thing that’s not visible in this chart is big gap between young and old. About 63 percent of millennials support legalization, compared to 27 percent of those aged 69 to 86.

What has the effect been so far?

In many ways, it’s still too early to say. Legal marijuana is in its infancy and remains limited to a few parts of the country. What can be said is that there’s been no obvious calamity, no spike in crime or addiction to discredit the whole experiment.

Decriminalization has a slightly longer pedigree, and again it doesn’t seem to have led to any crisis in public health or criminal justice.

What’s next?

The next really big test will come in 2016, when at least five states are likely to have ballot initiatives on legalization. Massachusetts may well be on that list, and so will California, where a victory for legalization would affect nearly 40 million people. And because 2016 is a presidential election year, which brings out younger and more marijuana-friendly voters, the odds will favor legalization.

Soon, legal marijuana may cease to be a fringe experiment and become a widespread norm. But at that point, the state-by-state approach may face a new and powerful enemy: international law.

Even though President Obama has agreed not to interfere with state marijuana laws, the US government officially considers marijuana more dangerous than cocaine and meth — and it has signed an international treaty that bans legalization. Ultimately, it may not be enough for marijuana’s supporters to keep winning state referenda. They may have to hope that the US government embraces legalization and attracts enough sympathetic allies to force a rewriting of international rules.