Just 10 years ago, no state in the US had legalized marijuana for recreational purposes.

Today, marijuana is legal for recreational purposes in 11 states and Washington, DC — including Illinois and Michigan, which legalized it in the past year. According to RAND drug policy expert Beau Kilmer, more than a quarter of the US population now lives in a state that allows marijuana for nonmedical purposes.

More is very likely coming: State legislatures, particularly across the Northeast, are openly discussing legalization, and several other states, such as Florida and Arizona, might expand by ballot initiative. The majority of Democratic presidential candidates have gotten behind legalization. And surveys have consistently found that most Americans support legalizing cannabis.

At the same time, even some advocates of legalization worry about how legalization is playing out in the states — with concerns that a “Big Marijuana” industry may be able to market pot irresponsibly, as tobacco, alcohol, and opioid companies have. And while marijuana is nowhere as risky as these other legal drugs, it still poses risks — notably, the possibility of addiction.

Still, the momentum appears to be on marijuana legalization’s side, with states from New York to Florida to Arizona considered potential candidates for legalization in the next few years.

Particularly as politicians and activists grow more critical of mass incarceration and the war on drugs, the legalization of a drug not many see as very harmful, if harmful at all, is widely perceived as an easy — and popular — place to start reforming criminal justice and drug policies.

1) Where is marijuana legal?

In 2012, Colorado and Washington state became the first states to vote to legalize marijuana for recreational purposes. Since then, nine more states and Washington, DC, have followed.

The laws legalize marijuana for people 21 and older, much like alcohol (and some tobacco) laws. They allow growing marijuana, with a limit on how many plants are allowed. There is also some variation in how much cannabis someone can legally possess, with visitors from outside the state facing stricter limits.

Vermont and DC don’t allow sales, meaning it’s still not legal to buy and sell pot in either jurisdiction — though residents in both places can legally grow it. And in DC, the allowance of “gifting” has led to some vendors, in a legally dubious practice, selling products like juices or decals that come with “gifts” of marijuana. (Not surprisingly, the juices and decals are very overpriced.)

In the 10 other states that have legalized, legal sales are on their way or already underway. Even in these states, though, local jurisdictions can decline to allow marijuana sales within their borders.

Some places that have legalized have also made the change effectively retroactive, erasing criminal records for past marijuana offenses. In California, for example, it’s possible to petition a court to get low-level offenses eliminated from the record and high-level offenses downgraded. In Illinois, the state government is automatically pardoning and expunging past offenses.

Meanwhile, Canada and Uruguay are the only countries to fully legalize marijuana. (The Netherlands, despite its reputation, has not fully legalized pot.)

2) What are the differences between legalization, decriminalization, and medical marijuana?

There is no set definition for any of these terms, and different advocates and politicians will use some of them, particularly legalization and decriminalization, interchangeably in a way that can be very confusing.

But here’s a broad overview of what these three categories are generally taken to mean:

Marijuana legalization: Legalization is generally taken to represent the removal of all government-enforced penalties for possessing and using marijuana. In most, but not all, cases, legalization also paves the way for the legal sales and home-growing of marijuana.

Marijuana decriminalization: Decriminalization generally eliminates jail or prison time for limited possession of marijuana, but some other penalties remain in place, treating a minor marijuana offense more like a minor traffic violation. Those caught possessing or selling an amount within the decriminalized limits are still fined — usually no more than a few hundred dollars. States with stricter decriminalization laws can also attach some jail or prison time to possessing larger amounts of marijuana, sales, or trafficking.

Medical marijuana: Medical legalization lets doctors recommend marijuana for a variety of conditions, from pain to nausea to inflammatory bowel disease to PTSD. A review of the evidence from the National Academies of Sciences, Engineering, and Medicine found little evidence for pot’s ability to treat health conditions outside chronic pain, chemotherapy-induced nausea and vomiting, and patient-reported multiple sclerosis spasticity symptoms. But most states, relying largely on anecdotal evidence, have allowed medical marijuana for many other conditions. And in a few states, medical cannabis laws have been so lax that they may as well be full legalization.

These three categories don’t cover the full array of options for marijuana reform, with a 2015 report by RAND listing a dozen alternatives to the standard prohibition of pot. Among the possibilities: legalizing possession but not sales (as DC and Vermont have done), putting state agencies in charge of sales (as some Canadian provinces are doing, and as some states do, successfully, with alcohol), allowing only nonprofit organizations to sell pot, or permitting only a handful of closely monitored for-profit companies to take part.

So far, though, the states that have legalized marijuana have generally allowed a for-profit industry, as is true for drugs like tobacco and alcohol — what RAND called the “standard commercial model.” The hope under this system is that the government will be able to tax and regulate the industry to allow responsible use while discouraging riskier behaviors.

But the US has a bad record of doing this with other drugs — allowing, for instance, drugmakers to irresponsibly market opioids for years and enable a major drug overdose crisis. So some experts, even those who favor legalization, prefer the alternative approaches to reform that RAND detailed.

3) What’s the case for marijuana legalization?

Supporters of legalization say prohibition has failed to significantly reduce access to and use of marijuana, while wasting billions of dollars and resulting in hundreds of thousands of racially skewed arrests each year. Legalization, by comparison, would allow people to use a relatively safe substance without the threat of arrest, and let all levels of government raise new revenues from pot sales and redirect resources to bigger needs.

A 2013 report by the American Civil Liberties Union found that there are several hundred thousand arrests for marijuana possession each year. These arrests are hugely skewed by race: Black and white Americans use marijuana at similar rates, but black people were 3.7 times more likely to be arrested than white Americans for marijuana possession in 2010.

The arrests not only cost law enforcement time and money, they also damage the government’s credibility. Former DC Police Chief Cathy Lanier explained in early 2015, “All those arrests do is make people hate us. … Marijuana smokers are not going to attack and kill a cop. They just want to get a bag of chips and relax. Alcohol is a much bigger problem.”

At the same time, prohibition has failed to notably reduce marijuana use. The war on drugs was originally intended to take down the supply of illegal drugs, increase prices as a result, and make drugs less affordable and generally less accessible. Those goals by and large failed: The White House’s Office of National Drug Control Policy found that marijuana prices dropped and stabilized after the early 1990s, and several surveys show marijuana use rose and stabilized among youth in the same time period.

Meanwhile, drug prohibition has created a lucrative black market for drug cartels and other criminal enterprises. Previous studies from the Mexican Institute of Competitiveness and the RAND Corporation suggested that marijuana at one point made up roughly 20 to 30 percent of drug cartels’ revenue. Through legalization, criminal groups lose much of that revenue, as sales transition to a legal market, crippling resources these organizations use to carry out violent operations around the world.

Federal legalization would also let the federal government tax sales to fund new programs, including treatment for people with drug use disorders. Previous estimates put this in the billions, if not tens of billions, of dollars for all levels of government — not nothing, but also not that much. (The federal budget for fiscal year 2019 was more than $4 trillion.)

More broadly, the legalization movement falls into a broader shift against the harsh criminal justice policies that came out of the war on drugs. As Americans look for alternatives to punitive prison sentences that turned the US into the world’s leader in incarceration, legalizing a relatively safe drug seems like low-hanging fruit.

And, of course, some people just want to be able to toke up without the government getting in the way.

4) What’s the case against marijuana legalization?

Opponents of legalization worry that fully allowing recreational marijuana use would make pot far too accessible and, as a result, expand its use and misuse.

The major concern is that letting for-profit businesses — “Big Marijuana” — market and sell cannabis may lead them to market aggressively to heavy pot users, who may have a drug problem. This is similar to what’s happened in the alcohol and tobacco industries, where companies make much of their profits from users with serious addiction issues. Among alcohol users, for instance, the top 10 percent of users consume, on average, more than 10 drinks each day.

Marijuana users exhibit similar patterns. In Colorado, a 2014 study of the state’s marijuana market, conducted by the Marijuana Policy Group for the state’s Department of Revenue, found the top 29.9 percent heaviest pot users in Colorado made up 87.1 percent of demand for the drug. For the marijuana industry, that makes the heaviest users the most lucrative customers.

Marijuana doesn’t pose the same risks as, say, cocaine, heroin, or even legal substances like alcohol. But opponents of legalization argue that heavy use can still signify addiction, which means someone may really want to stop using pot but can’t despite negative consequences — hurting his personal life, education, career, and potentially health.

Kevin Sabet, head of Smart Approaches to Marijuana (SAM), the nation’s leading anti-legalization group, previously explained: “If we were a country with a history of being able to promote moderation in our consumer use of products, or promote responsible corporate advertising or no advertising, or if we had a history of being able to take taxes gained from a vice and redirect them into some positive areas, I might be less concerned about what I see happening in this country. But I think we have a horrible history of dealing with these kinds of things.”

Drug policy experts say there are alternatives to commercial legalization, like putting state governments in charge of marijuana production and sales, which could tame the for-profit incentive and give states more direct control over prices and who buys pot.

But legalization opponents worry that any move toward legalization will inevitably attract powerful for-profit forces, especially since the marijuana industry has already taken off in several states. “The reality is there are myriad other forces at work here,” Sabet said. “Chief among them are the very powerful forces of greed and profit. When I look at how things are set up in states like Colorado, where the marijuana industry gets a seat at the table for every state decision on marijuana policy, it troubles me.”

Given these concerns, opponents favor more limited reforms than legalization. Sabet, for example, said nonviolent marijuana users shouldn’t be incarcerated for the drug. Other critics of legalization support legalizing marijuana for medical purposes but not recreational use.

It’s rare that opponents of legalization argue for the full continuation of the current war on pot. SAM, for instance, broadly agrees that current drug and criminal justice policies are far too punitive and costly. But while they may support some reforms, they feel that legalization simply goes too far — and could lead to worse consequences than the alternatives.

5) Is marijuana bad for your health?

There are no documented deaths from a marijuana overdose, but that doesn’t mean pot is harmless.

“The main risk of cannabis is losing control of your cannabis intake,” Mark Kleiman, a drug policy expert who recently passed away, previously told me. “That’s going to have consequences in terms of the amount of time you spend not fully functional. When that’s hours per day times years, that’s bad.”

Jon Caulkins, a drug policy expert at Carnegie Mellon University, put it another way: “At some level, we know that spending more than half of your waking hours intoxicated for years and years on end is not increasing the likelihood that you’ll win a Pulitzer Prize or discover the cure for cancer.”

The risk of misuse and addiction (known in medical circles as “cannabis use disorder”) is compounded by the widespread perception that pot is harmless: Since many marijuana users believe what they’re doing won’t hurt them, they feel much more comfortable falling into a habit of constantly using the drug. In total, millions of people across the US report wanting to quit marijuana and being unable to despite negative consequences.

The most thorough review of the research yet, from the National Academies of Sciences, Engineering, and Medicine, linked marijuana use to a variety of other potential downsides, including respiratory issues (if smoked), schizophrenia and psychosis, car crashes, lagging academic and other social achievements, and lower birth weight (if smoked during pregnancy).

But it doesn’t seem to cause some issues that are typically linked to tobacco, particularly lung cancer and head and neck cancers. The studies reviewed also suggest it carries several benefits, particularly for chronic pain, multiple sclerosis, and chemotherapy-induced nausea and vomiting. (There wasn’t enough research to gauge if pot is truly good for some of the other ailments people say it’s good for, such as epilepsy and irritable bowel syndrome.)

The National Academies report emphasized that more research is needed, with a lot of unknowns remaining about marijuana use and its effects. For one, the research has yet to prove if all the problems correlated with cannabis use are actually caused by pot. (After all, correlation is not causation.)

Critics of legalization also claim that marijuana is a “gateway drug” that can lead people to try more dangerous drugs like cocaine and heroin, because there’s a correlation between pot use and use of harder drugs. But researchers argue that this correlation may just indicate that people prone to all sorts of drug use only start with marijuana because it’s the cheapest and most accessible of the illicit drugs. So if cocaine or heroin were cheaper and more accessible, there’s a good chance people would start with those drugs first.

Overall, marijuana is a relatively safe drug — certainly less harmful than some of the drugs that are legal today, and potentially beneficial to some people’s health through its medical use. But it’s not harmless.

Given that marijuana’s harms appear to be relatively small, though, advocates argue that even if legalization leads to more pot use, it’s worth the benefits of reducing incarceration and crippling violent drug cartels financed in part by revenue from illicit weed sales.

6) Is marijuana legalization popular?

It sure seems like it.

According to surveys from Gallup, support for legalization rose from 12 percent in 1969 to 31 percent in 2000 to 66 percent in 2018. A Civic Science poll and the General Social Survey found similar levels of support in recent years.

The Pew Research Center found that support varies from generation to generation, although it has been rising among all age groups over the past few years. As it stands, more than two-thirds of millennials back legalizing marijuana, while support is lower among older groups.

The change in public opinion is part of a broader pushback against punitive criminal justice policies and the war on drugs in general. A 2014 Pew survey found 63 percent of Americans agree states should move away from harsh mandatory minimum sentences for nonviolent drug crimes, and 67 percent said drug policy should focus more on providing treatment over prosecuting drug users.

The wider shift on all punitive drug policies demonstrates that it’s not just that more Americans want the freedom to use marijuana — a substance that more than six in 10, according to Pew, acknowledge is safer for a person’s health and society than alcohol. Instead, Americans are broadly fed up with drug and criminal justice policies that have contributed to higher incarceration rates while doing little to solve ongoing drug crises.

7) Is marijuana still illegal at the federal level?

Yes. Even as several states and Washington, DC, allow marijuana, the federal government still strictly prohibits pot.

Under the scheduling system, the federal government classifies marijuana as a schedule 1 drug, meaning it’s perceived to have no medical value and a high potential for abuse. That classification puts marijuana in the same category as heroin and a more restrictive category than schedule 2 drugs like cocaine and meth.

But that doesn’t mean the federal government views marijuana and heroin as equally dangerous drugs or that it considers marijuana to be more dangerous than meth or cocaine. Schedule 1 and 2 drugs are both described as having “a high potential for abuse” — a vague description that doesn’t rank drugs in the two categories as equal or different.

The big distinction between schedule 1 and 2 substances, instead, is whether the federal government thinks a drug has medical value. The DEA says schedule 2 substances have some medical value and schedule 1 substances do not, so schedule 1 drugs receive more regulatory scrutiny even though they may not be more dangerous.

There have been many calls to reschedule marijuana, but they’ve run into a serious hurdle: To date, there have been no large-scale clinical trials on marijuana. Those kinds of studies are traditionally required to prove a drug has medical value to the federal government. But these studies are also much more difficult to conduct when a substance is strictly regulated by the federal government as a schedule 1 drug. So pot is essentially trapped in a Catch-22: It likely needs a large-scale clinical trial to be rescheduled, but those trials are going to be much harder to conduct until it’s reclassified.

Congress can also pass legislation to reschedule marijuana, which legalization advocates have been lobbying legislators to do for decades.

Although the scheduling system helps shape criminal penalties for illicit drug possession and sales, it’s not always the final word. Penalties for marijuana are generally far more relaxed than other schedule 1 drugs — partly an acknowledgment that the drug isn’t as much of a risk as, for example, heroin.

Starting with the Obama administration, the federal government has also taken a relaxed approach to marijuana legalization at the state level, generally letting states do as they wish as long as they met certain criteria (such as not letting legal pot fall into kids’ hands or cross state lines). The Trump administration suggested it would take a tougher line under Attorney General Jeff Sessions, but current Attorney General William Barr backed off the tougher approach and said he would more or less go back to the Obama-era policies.

Pot’s criminal classification at the federal level has other serious ramifications for marijuana policy even in places where state law says the drug is legal. Many state-legal marijuana businesses, for instance, must function as cash-only enterprises, since many banks are nervous about dealing with businesses that are essentially breaking federal law. Businesses also can’t file for several deductions, and, as a result, their effective income tax rates can soar to as high as 90 percent or more.

One concern here is whether the federal government would be in violation of international law if it legalized marijuana. A host of international treaties explicitly ban the legalization of marijuana sales for recreational purposes. As states have legalized, the US has argued that it remains in good standing of these treaties by keeping pot illegal at the federal level. But that would change if Congress and the president legalized marijuana. (So far, Canada and Uruguay have generally dodged scrutiny over their violation of these treaties. But the US is a much bigger country than either.)

So even as states and voters back marijuana legalization, the federal government remains in the way.

8) How is marijuana legalization going in the states that have done it so far?

So far, it seems to be going fine. Then-Colorado Gov. John Hickenlooper opposed legalization when it was on the ballot in his state, but he has since acknowledged that “the things I feared six years ago have not come to pass.”

Colorado, which has the oldest system for recreational marijuana sales, has seen a rise in adult use, but not in use among youth. Although there were concerns about drug-impaired car crashes, the evidence is mixed.

One concern that has consistently come up is the risk of marijuana edibles, which a recent study linked to a rapid increase in marijuana-related hospitalizations at a Colorado hospital after legalization. Because edibles take longer to take effect, and may lead the human body to absorb the psychoactive compounds of cannabis differently, they’re more likely to cause a marijuana overdose — not a deadly event, but one that can make people act strange and paranoid. The proliferation of edibles under legalization, then, may be leading to more bad, unpleasant trips.

Critics of legalization also argue that edibles are marketed irresponsibly, since they can take the form of child-friendly snacks like gummy bears and cereals.

So since legalization, regulators have taken a tougher approach toward edibles — restricting them, requiring stronger packaging and labels, and even banning some of them.

The story is broadly similar in other states, with some variation depending on state-specific circumstances. No big negative stories have come out of legalization, at least yet.

That said, it’s worth cautioning that recreational legalization is fairly young. The marijuana industry is still taking form. Federal prohibition has made it hard for the industry to grow in a big way, since they can’t very easily operate across state lines. How this new industry, its marketing, and its influence over all levels of government take shape in the next few years — and ultimately influence people’s behaviors — remain very big questions for experts.

As Kleiman, who supported legalization, used to tell me, “The bad risks are mostly long-term. We’re in the situation in which the guy jumped off the Empire State Building, and as he passed the 42nd floor somebody said, ‘How’s it going?’ And he said, ‘So far, so good!’”

9) Which states could legalize marijuana next?

Most of the states that have legalized to this point have done so through ballot initiatives, but that’s changed in recent years with state legislatures in Vermont and Illinois approving legalization. So now there are two plausible paths to legalization.

On the state legislature side, the most serious conversations seem to be taking place in New York and New Jersey, where governors have gotten strongly behind legalization but have so far struggled to get bills through the legislatures. There’s also been movement in Connecticut, Delaware, Rhode Island, and Vermont (to legalize sales), among other places.

Plus, there are some upcoming legalization ballot initiatives, potentially in Arizona, Florida, and North Dakota.

There could also be a few surprises. Who could have predicted just five years ago that Michigan would legalize pot before New York, New Jersey, and half the states in New England? It’s a weird world — one where marijuana is increasingly legal.