SAN FRANCISCO (CBS SF) — California voters passed a ballot measure to legalize the recreational use of marijuana, giving a big boost to the campaign to end the drug’s national prohibition.

A preliminary exit poll conducted for The Associated Press and television networks by Edison Research found Proposition 64 passing by a margin of 55 percent in favor of the proposition to 45 percent voting against.

Adults older than 21 years old can legally possess up to an ounce of marijuana and grow six plants.

California was one of five states where votes were considering the legalization of recreational marijuana Tuesday. Massachusetts and Nevada also voted to legalize the recreational use of marijuana, giving a huge boost to the campaign to allow pot nationwide.

Voters in Arkansas, Florida and North Dakota approved measures allowing marijuana use for medical purposes. Montanans voted on whether to ease restrictions on an existing medical marijuana law.

Florida, where the pot measure was backed by 71 percent of the voters, and Arkansas became the first states in the South with full-scale medical marijuana programs, which exist in 25 other states.

Collectively, it was the closest the U.S. has ever come to a national referendum on marijuana, which remains prohibited under federal law.

“These votes send a clear message to federal officials that it’s time to stop arresting and incarcerating marijuana users,” said Rob Kampia, executive director of the pro-legalization Marijuana Policy Project.

If “yes” votes prevailed across the board, more than 23 percent of the U.S. population will live in states where recreational pot is legal. The jurisdictions where that’s already the case — Alaska, Colorado, Oregon, Washington state and the District of Columbia — have less than 6 percent of the population.

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