More than half of Americans support legalizing marijuana use, according to a Pew Research Center poll, and two states — Washington and Colorado — are the first to allow adults to use the drug for recreational purposes. Meanwhile, 24 states and the District of Columbia allow marijuana use for medical reasons or have decriminalized the drug. The Obama administration’s stance on enforcing federal laws barring marijuana use in Washington and Colorado remains unclear. Organizations opposed to liberalizing marijuana laws hope to get the administration to take a tougher line in states that have legalized medical or recreational use. Meanwhile, 22.5 million Americans — including one in 10 youths between 12 and 17 — reported using drugs in 2011. So-called synthetic marijuana, a new drug also known as “Spice” or “K2,” has risen sharply in popularity among teens.

Robyn Bowen of Seattle smokes marijuana beneath the Space Needle shortly after a law legalizing the drug’s recreational use by adults took effect on Dec. 6, 2012, in Washington. Last November, Washington and Colorado became the first states to allow such use. (Getty Images/Stephen Brashear)

Last November, Washington and Colorado became the first states to allow adults to use marijuana for recreational purposes.

The historic moves contributed to a growing divide between state and federal laws. While federal law still categorizes marijuana as a Schedule 1, or controlled, substance like heroin and crack cocaine, in the past two decades 24 states plus the District of Columbia have allowed marijuana use for medical purposes or have decriminalized it — making possession of small amounts of pot an offense akin to a traffic violation.