WASHINGTON -- Legalizing marijuana in even a single state could drive down prices dramatically across the country, encouraging more people to smoke the drug, a panel of experts said at a briefing Tuesday.

Last week, Oregon became the third state that will vote this November on a ballot measure to legalize marijuana, joining Colorado and Washington.

“Legalization is unprecedented – not even the Netherlands has done it – it is entirely possible it will happen this year,” said Jonathan Caulkins, co-author of "Marijuana Legalization: What Everyone Needs to Know."

“The effects will be enormous,” said Caulkins, a professor at Carnegie Mellon, during an event at the American Enterprise Institute.

The Obama administration opposes legalizing marijuana and has taken action to shut down some medical marijuana dispensaries in California and Colorado.

Caulkins said one of the main reasons for outlawing the drug is to make it riskier to produce and sell, driving up prices and curbing use. A price collapse following legalization in some states could undermine marijuana laws nationally, the experts warned.