Last week, voters in Colorado and Washington State approved ballot initiatives legalizing marijuana for the first time in the United States since the 1930s. Both measures—Colorado’s Amendment 64 and Washington’s Initiative 502—regulate and tax the sale and possession of up to an ounce of marijuana in much the same way as alcohol. As a result, state-level marijuana policies now vary widely, including everything from complete prohibition to decriminalization of small amounts (for example, making it a ticketable rather than criminal offense) to allowances for medical use to complete legalization.

In practice, this means that in New York City, more than 50,000 people were arrested for possession of small amounts of marijuana in 2010; on the opposite coast, Washington State residents will soon be able to buy up to an ounce of marijuana at a licensed store with no legal repercussions. When it comes to marijuana policy, the country is deeply divided.While the most recent legislation is contentious—particularly given its conflict with federal statute defining marijuana as a prohibited substance—it provides researchers with a unique opportunity. The variation in marijuana regulation throughout the United States makes it possible for the research community to begin to study the range of approaches. The empirical data that such research yields can inform the ongoing debate on U.S. drug policy.

Changes in the law create natural experiments that allow researchers to study policy as it plays out in the real world, which may not conform to the intentions of the written legislation; Vera’s study of the changes to New York State’s drug statutes (known as the “Rockefeller drug laws”) is one example of this type of work. Ensuring that marijuana policy is based on evidence rather than rhetoric is of paramount importance, given its relevance to such a wide swath of the American public; according to the 2010 National Survey on Drug Use and Health conducted by the Substance Abuse and Mental Health Services Administration, about 7 percent of the U.S. population, or 17.4 million people, had used marijuana in the previous month. Furthermore, recent polls suggest that at least 50 percent of Americans support legalization of small quantities of the drug, and 70 percent favor legalization for medical purposes, making it an issue that policymakers will have to reconsider.

To contribute to the public conversation about marijuana policies, researchers must take a holistic approach, assessing not only substance use and criminal justice outcomes, but also examining monetary costs of different policy approaches and impacts on individuals, such as employment and educational outcomes (for instance, missed work arising from a marijuana arrest, or decreased academic performance associated with marijuana use). These are complex issues that affect millions of Americans, and the evidence will take time to disentangle. For example, it is important to consider the evidence for the disproportionate impact of marijuana policing practices in New York City on black and Latino communities alongside evidence that states that have legalized medical marijuana have higher rates of use among residents than states without these laws.

It is the ethical responsibility of researchers to ensure that study findings are communicated accurately—with all caveats and biases on display. Marijuana policy is a morally and politically charged issue that ultimately requires value judgments about the relative weights of a variety of harms and benefits—but researchers can help ensure that those valuations are as informed as possible. Thus, as Colorado and Washington roll out their new marijuana laws, researchers should begin to evaluate the policies and compare them to the other approaches throughout the country. While location matters—New York City will never be Seattle or Boulder—state legislators can learn from the experiences of other jurisdictions as they develop sound drug policy that yields the best outcomes for justice and safety.