Polls show changing American opinion on marijuana, and it's having an effect on politics. Leon Neal/AFP/Getty Images hide caption

itoggle caption Leon Neal/AFP/Getty Images

Leaders of the Alaska Cannabis Club share a joint at their medical marijuana dispensary in Anchorage. On Tuesday, Alaska became the third state in the nation to legalize recreational marijuana use. Mark Thiessen/AP hide caption

itoggle caption Mark Thiessen/AP

Deuel County Sheriff Adam Hayward shows off a container of confiscated marijuana in Chappell, Neb., in July. Nikki Kahn/The Washington Post/Getty Images hide caption

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A marijuana bud displayed in Denver. Don't legalize pot, the pediatricians say, but don't lock teenagers up for using it, either. Seth McConnell/The Denver Post/Getty Images hide caption

itoggle caption Seth McConnell/The Denver Post/Getty Images

Adam Eidinger, chairman of the D.C. Cannabis Campaign, puts up Initiative 71 posters in October. The measure to legalize possession of up to 2 ounces of marijuana was approved by a wide margin of local voters. Jacquelyn Martin/AP hide caption

itoggle caption Jacquelyn Martin/AP

Officials in Aspen have put out a brochure on how to use marijuana safely and legally. Marci Krivonen hide caption

itoggle caption Marci Krivonen

Nebraska and Oklahoma say Colorado's marijuana law is unconstitutional, in a challenge to the law in the Supreme Court. Earlier this month, visitors from Texas smell marijuana at the Breckenridge Cannabis Club. Brennan Linsley/AP hide caption

itoggle caption Brennan Linsley/AP

Volunteers with the DC Cannabis Campaign (left and center) talk to a voter on Election Day about the ballot initiative to legalize marijuana. The measure was approved, but its fate remains uncertain. Allison Shelley/Getty Images hide caption

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Trimmers prepare the marijuana flower, or bud, to make it more appealing to consumers. They use scissors to snip off the leaves and stems. Brett Myers/Youth Radio hide caption

itoggle caption Brett Myers/Youth Radio

Nabor, a small-scale marijuana grower in the northwestern Mexican state of Sinoloa, checks his plants. As legal pot increasingly becomes available in the U.S., Americans appear to be buying more that is grown domestically. Prices for marijuana from Mexico have fallen sharply. John Burnett/NPR hide caption

itoggle caption John Burnett/NPR

Early results showed more than a 2-1 lead for a measure to make recreational marijuana use legal in Washington, D.C. A sign promoting the initiative is seen on a corner in the Adams Morgan neighborhood Tuesday. Allison Shelley/Getty Images hide caption

itoggle caption Allison Shelley/Getty Images

Low-dose pot-infused cookies, called the Rookie Cookie, sit on the packaging table Sept. 26 at The Growing Kitchen in Boulder, Colo. The state legalized recreational pot use last year. Brennan Linsley/AP hide caption

itoggle caption Brennan Linsley/AP

This human-scale lab rat cage is parked near a skate park in Denver, Colo., to make a point about the lack of science on marijuana. Richard Feldman Studio/Sukle Advertising and Design hide caption

itoggle caption Richard Feldman Studio/Sukle Advertising and Design

Edibles available at LoDo Wellness Center, a retail marijuana and medical marijuana dispensary and grow facility in downtown Denver. Matthew Staver/Landov hide caption

itoggle caption Matthew Staver/Landov