When the Canadian Parliament considered decriminalizing marijuana possession in 2003, U.S. officials loudly objected. They complained that the proposed reform would betray the anti-drug cause, worried that it would encourage drug tourism and facilitate marijuana smuggling, and threatened to respond with a border crackdown that would impede trade and travel between the two countries.

Canadian legislators got the message. The marijuana bill, which would have made possessing up to 15 grams (about half an ounce) of marijuana a civil offense punishable by a fine and reduced the penalties for home cultivation of up to seven plants, never got a vote.

Thirteen years later, those reforms look timid compared to the laws approved by four U.S. states, which remove all penalties for possession and (in three states) home cultivation while allowing commercial production and distribution. Even the nation's capital lets adults 21 or older grow, possess, and share marijuana without penalties, although pot shops are on hold because of congressional objections. As Canada's new government proceeds with its plans to legalize marijuana, it is following America's example.

That striking reversal reflects a new reality that was underscored by last week's U.N. General Assembly special session on "the world drug problem," the first such gathering since 1998. The United States, which used to be the country pushing others to be tough on drugs, is now at the forefront of reform. As a result, instead of portraying any deviation from prohibitionist orthodoxy as a grave violation of international obligations, the U.S. is supporting a flexible interpretation of drug control treaties that leaves room even for bold changes like drug legalization.

Last month William Brownfield, the assistant secretary of state for international narcotics and law enforcement affairs, told reporters cooperation on drug policy should be based on four principles: "Defend the integrity of the [drug control] conventions, accept the inherent discretion within those conventions, tolerance for governments exploring their own national policies, and a commitment to combating the transnational criminal organizations." Ideally, the tolerance for diverse policies that Brownfield advocates would work at the international level the way federalism is supposed to work in the U.S.: Different jurisdictions take different approaches and learn from each other's experiences.

So what can other countries learn from the U.S. experience with marijuana legalization? While it's too early to draw firm conclusions, a recent report from the Colorado Department of Public Safety (CDPS) suggests a few tentative observations:

Less criminalization means fewer criminals.

The most obvious thing that happens when a government stops punishing people for certain marijuana-related activities—so obvious that it's often overlooked—is that marijuana arrests and prosecutions drop precipitously. Marijuana arrests in Colorado fell from 12,894 in 2012, when voters approved legalization, to 7,004 in 2014, the first year of legal recreational sales—a 46 percent decrease. Marijuana charges filed in Colorado courts fell 81 percent between 2012 and 2015, from 10,340 to 1,954. Those dramatic changes saved thousands of people from unjust punishment and channeled law enforcement resources toward activities with a bigger public safety payoff.

Legal marijuana does not seem to encourage crime.

Prohibitionists sometimes imply that legalization has boosted crime in Colorado, but there is little evidence of that. Colorado's property crime rate fell by 5 percent between 2012 and 2015, while its violent crime rate rose by 1 percent. Since 2009, when the medical marijuana industry in Colorado started to take off, both rates have fallen—by 3 percent and 6 percent, respectively.

Legalization's impact on traffic safety is unclear so far.

The Colorado State Patrol began collecting information on the drug involved in driving under the influence (DUI) cases only in 2014. DUI summonses involving marijuana (either alone or in combination with other drugs, usually alcohol) fell 1 percent between 2014 and 2015. The Denver Police Department, which started keeping track of these numbers a year earlier, found that marijuana-related DUI citations doubled between 2013 and 2014 (from 33 to 66), then rose again in 2015, from 66 to 73.

These figures are affected not only by the prevalence of stoned driving but by enforcement priorities and police awareness, which has been heightened by legalization. Furthermore, even when a DUI suspicion is substantiated by tests showing THC in a driver's blood, that does not necessarily mean he was impaired while he was driving. As the report notes, "the detection of any THC in blood is not an indicator of impairment but only indicates presence in the system." When marijuana consumption rises in the general population, the percentage of drivers who test positive for THC will rise too, even if they are not actually stoned behind the wheel.

The same problem affects interpretation of traffic fatality numbers. CDPS reports that "fatalities with THC?only or THC?in?combination positive drivers increased 44 percent, from 55 in 2013 to 79 in 2014." It's not clear how much of a role, if any, marijuana played in those accidents, since even unimpaired cannabis consumers can test positive for THC.

Legalization makes adults more likely to consume cannabis—or maybe just more likely to admit it.

Survey data indicate that cannabis consumption in Colorado has risen since legalization. According to the National Survey on Drug Use and Health (NSDUH), the share of 18-to-25-year-olds reporting marijuana use in the previous month rose from 26.8 percent in 2012 to 31.2 percent in 2014, continuing an upward trend that began in 2006. The same rate rose from 7.6 percent to 12.4 percent among adults 26 and older, an age group in which cannabis consumption had risen and fallen during the previous six years. Both post-2012 increases paralleled a national trend but were more substantial.

Some caution is appropriate when interpreting survey results like these, since subjects' willingness to admit marijuana use may depend on the drug's legal status and its social acceptability. Hence some of the increase in reported use may reflect greater candor rather than greater consumption. As the CDPS report notes, "The decreasing social stigma regarding marijuana use could lead individuals to be more likely to report use on surveys…making marijuana use appear to increase when perhaps it has not."

The evidence concerning marijuana consumption by teenagers is mixed.

The Healthy Kids Colorado Survey, which is conducted every two years, found that the rate of past-month marijuana use by 12-to-17-year-olds fell from 22 percent in 2011 to 19.7 percent in 2013. NSDUH, by contrast, measured an increase, from 10.5 percent in 2012 to 12.6 percent in 2014, although the change was not statistically significant. This NSDUH estimate has been rising more or less steadily since 2006, so the post-2012 increase may or may not be related to legalization.

After legalization, marijuana mentions in medical records become more common.

According to data compiled by the Colorado Department of Public Health and Environment, 2.4 percent of hospitalization records included references to marijuana during the 18-month period ending on June 30, 2015, up from 1.4 percent in the period from 2010 through 2013. Meanwhile, the share of emergency room cases in which marijuana was mentioned rose from 0.7 percent to about 1 percent. CDPS notes that such a mention "does not mean that the visit is motivated by marijuana exposure but simply that it is a possibility."

These numbers may reflect an increase in marijuana-related medical issues tied to an increase in consumption. But they also may reflect a greater prevalence of marijuana use among patients (whether or not it contributed to their problem), a greater willingness among patients to report marijuana use, and a greater inclination among medical personnel to ask about marijuana use and make a note of it.

Easier availability of marijuana may boost calls to poison control centers.

Marijuana-related calls to the Rocky Mountain Poison and Drug Center (RMPDC) more than doubled after legalization, from 109 in 2012 to 227 in 2015. While that increase may be partly due to increased openness about cannabis, it's plausible that some of it is related to easier availability of marijuana products. Last year about a fifth of the marijuana calls involved children 8 or younger, who may have accidentally consumed marijuana edibles. Nearly half of the calls involved adults 18 or older, who presumably consumed marijuana on purpose in most cases but may have inadvertently taken an uncomfortably high dose. A mixture of those explanations probably applies to calls involving 9-to-17-year-olds, almost a third of the total.

Marijuana still accounts for a tiny fraction of the 50,000 or so calls the RMPDC receives each year. Although the RMPDC does not report outcomes, data from Washington Poison Center suggest they are rarely serious. Still, reactions to marijuana that prompt calls to a poison control center qualify as a genuine problem, and it's one that could be curbed through consumer education, focusing especially on the potential pitfalls of edibles. By allowing such open discussion of careful consumption habits, legalization could ultimately reduce the percentage of users who have bad reactions to marijuana.

Respecting human rights means respecting human choices (even the bad ones).

Yuri Fedotov, executive director of the U.N. Office on Drugs and Crime, told the Los Angeles Times this week's special session "is about putting people first." According to Fedotov, "This means supporting health and human rights, promoting the safety and security of all our societies, emphasizing the role of the international drug control conventions in promoting the health and welfare of humankind, and acknowledging that every country has a shared responsibility to confront this issue."

That recipe includes an unhealthy helping of paternalism, which is how drug warriors justify using force to suppress the use of potentially harmful substances. Imagine if "putting people first" meant treating them like adults capable of making their own decisions and learning from their mistakes. A marijuana policy based on that approach would look a lot like what is happening in Colorado right now.

This article originally appeared at Forbes.com.