There has been a spike in illegal shipments of marijuana from Colorado to surrounding areas since the state legalized the drug, according to the head of the Drug Enforcement Administration (DEA). There has been a 61 percent increase in seizures of marijuana in Kansas that originated in Colorado.

Once recreational marijuana sales start in Washington state, a similar pattern could emerge, said DEA Administrator Michele Leonhart. She spoke Wednesday at a hearing of the Senate Judiciary Committee.

“The trends are what us in law enforcement had expected would happen,” she told the committee. “In 2012, 438,000 Americans were addicted to heroin. And 10 times that number were dependent on marijuana.” She pointed out marijuana-related emergency room visits rose by 28 percent between 2007 and 2011. She added that since 2009, more high school seniors have been smoking marijuana than smoking cigarettes.

Last August, the U.S. Justice Department announced it would allow Colorado and Washington to carry out their new recreational marijuana laws. The department said it would focus enforcement on criminal charges in specific areas, such as distribution to minors.

The announcement ended almost a year of debate within the Obama Administration about how to react to the state laws, which allow personal possession of up to an ounce of marijuana for anyone at least 21 years old. They also permit marijuana to be sold and taxed at state-licensed stores. Federal law outlaws the production, possession and sale of marijuana.

The Washington Post reports DEA officials privately have said they are frustrated with the two states’ legalization laws. In January, the DEA’s Chief of Operations, James Capra, told senators at a hearing that state legalization laws are “reckless and irresponsible.” “It scares us,” he said. “Every part of the world where this has been tried, it has failed time and time again.”