For the first time, two American states have legalized the recreational use and sale of marijuana

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For the first time, two American states have legalized the recreational use and sale of marijuana.

Voters in Colorado, Washington State and Oregon had the opportunity to make history by voting on initiatives that would legalize the recreational use and sale of marijuana in their respective states. Only residents of Oregon rejected the move. Massachusetts voters joined 17 states and the District of Columbia in electing to allow medical use of the drug.

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But the victories could create a clash over states’ rights since the federal government continues to consider marijuana — even for medical use — an illegal substance, and the possession, sale or distribution of marijuana a crime. Anticipating a confrontation, Colorado Governor John Hickenlooper warned celebrants not to “break out the Cheetos or Goldfish too quickly” as his administration figures out how state residents can buy and sell marijuana without running afoul of federal laws.

Joking, however, does not seem likely to stand in the way of change. The initiatives represent an increased public push for legalization; a 2011 Gallup poll found that 50% of Americans are in favor of marijuana legalization, up from just 12% in 1969. Support for medical marijuana is even higher — despite controversy over how often recreational use masquerades as medical need — and consistently averages over 70%. Three states had ballot questions on medical use; Massachusetts voters approved it, while those in Arkansas rejected the measure. Montana, which already allows such use, tightened its regulations.

(MORE: Medical Marijuana Finally Heads to D.C.)

What would legalized recreational use mean? For one thing, Colorado and Washington don’t simply lessen the penalties for users from criminal charges to fines. The states do legalize and tax sales — a step that not even countries like the Netherlands, where wholesale selling and growing is illegal but small retail sales are tolerated in licensed “coffee shops,” have taken.

Washington’s law involves a licensing regime, to be handled by the state’s liquor control board, for growers and sellers. Initiative 502 bans sales to people under 21 and sets a 25% tax on both wholesale and retail sales, which will be used to fund drug prevention, schools and health insurance.

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Unlike most prior initiatives, I-502 was widely supported by state officials and mainstream media, including the state Democratic Party and local newspapers. It sets a legal limit on THC blood levels for driving (THC is the active ingredient in cannabis). It also bans growing for personal, non-medical use.

Colorado’s new law is somewhat different: Amendment 64 allows personal possession and growing for one’s own use or to give away. Sales, however, will require a license from the state department of revenue and will be taxed to fund school construction, at a rate of up to 15%. The Colorado Legislative Council estimates that this could bring in between $4 million and $21 million annually, after accounting for initial costs of $1.3 million and $700,000 to fund the regulatory apparatus.

Both measures passed by comfortable margins — I-502 garnered an estimated 55% of support, and Amendment 64 earned 53% of the vote. Colorado’s enthusiasm is especially significant given that the state already has a medical-marijuana establishment, with 204 outlets in Denver — about three times its number of Starbucks and McDonald’s, combined.

The federal government, however, remains a cloud that hangs over the ballot victories. Since 2009, the Obama Administration has authorized at least 170 raids on dispensaries and issued more than 61 federal indictments, according to the Huffington Post. In justifying the actions, President Obama told Rolling Stone that “I can’t nullify congressional law. I can’t ask the Justice Department to say, ‘Ignore completely a federal law that’s on the books.’ What I can say is, ‘Use your prosecutorial discretion and properly prioritize your resources to go after things that are really doing folks damage.’ ”

The real question is how much damage legal marijuana sales could cause. Proponents argue that marijuana is less dangerous than alcohol or tobacco. Unlike alcohol, for example, marijuana does not often produce disinhibited behavior that triggers the risk of violence. And unlike tobacco, it does not appear to be linked with lung cancer or other common cancers; the largest and most careful studies simply have not yet found a connection, even in the heaviest smokers.

(MORE: Stoned Driving Nearly Doubles the Risk of a Fatal Crash)

THC, however, is a mild hallucinogen that also has sedative properties. Cannabis intoxication does impair memory and cognition, and marijuana addiction, as with any drug, can lead to serious impairments in judgment and result in harm. But experts agree that marijuana addiction tends to be less severe than cocaine, heroin, methamphetamine or alcohol addiction.

Whether marijuana’s status as a legal or illegal drug influences how it is used remains unclear. Studies conducted in Holland, which has come the closest to full legalization of cannabis, and Portugal, which decriminalized possession of all drugs, so far do not show negative effects on either addiction rates or misuse by young people.

There is also the complicated relationship between the intensity of law enforcement and the rates of marijuana use and addiction, with no clear expectation that increased enforcement will lower use or related problems. As Dr. Evan Wood, a professor of medicine at the University of British Columbia and the founder of the International Centre for Science in Drug Policy, says, “No scientific evidence demonstrates an association between the amount of money governments spend on drug law enforcement and rates of drug use. And some nations like the U.S., which spend the most, have among the highest rates of drug use.”

One factor that does influence drug use is price, and legal marijuana would almost certainly be cheaper than that on the black market. A study conducted while California voters considered legalization suggested that the price would drop by 80%.

(MORE: Will Marijuana Legalization Increase Use?)

If that’s true, and use increases, the states that now have a mandate permitting marijuana use may face another concern to public safety. Some research suggests that marijuana use substitutes for drinking, which would lower driving risks. Others studies, however, find that it is simply added on top, which makes drunk driving more dangerous. But one risk is clearly reduced by legalization: the harms related to arrest and incarceration, which are disproportionately borne by minorities. The voters have spoken. Now they’re waiting for the federal government to respond.

MORE: 10 Reasons to Revisit Marijuana Policy Now

Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.