Fifty-two percent say pot should be made legal while 45 percent say it should not in the Pew Research Center poll released Thursday.
The percentage of those supporting legalization rose 11 points since 2010. The change is even more dramatic since 1969, when a Gallup poll found just 12 percent said they favored legalizing marijuana use, while 84 percent said they opposed it.
The Pew poll results mirror a Quinnipiac University poll in December that found 51 percent of registered U.S. voters favored marijuana legalization while 44 percent didn't.
A November Washington Post-ABC News poll found the public split 48 percent to 50 percent on whether to legalize the possession of small amounts of marijuana for personal use.
The Pew poll found nearly half of Americans -- 48 percent -- say they have tried marijuana, up from 40 percent in 2010.
Of those who say they've used marijuana in the past year, 47 percent say they used it "just for fun," while 30 percent say it was for a medical issue.
Twenty-three percent volunteer they smoked pot for medical purposes and for fun.
Along with growing support for marijuana legalization has been a drop in the percentage of people saying they view pot as a "gateway drug."
Just 38 percent agree marijuana use leads to hard drugs for most people, the poll found. In 1977, 60 percent said it led to hard drugs.
In terms of morality, 1-in-3, or 32 percent, say smoking marijuana is wrong, down 18 points since 2006, when half the population called it wrong.
As attitudes change, the vast majority of Americans -- 72 percent -- say government efforts to enforce marijuana laws cost more than they are worth, and 6-in-10 Americans say federal laws should not be enforced in states that have decided to allow marijuana use.
In the fall elections, voters in Colorado and Washington state approved the personal use of small amounts of marijuana for recreational use.
Pew's phone poll of 1,501 adults ages 18 and over was conducted March 13-17. The overall margin of error is 2.9 percentage points. Results for the share of Americans smoking marijuana were based on a separate survey conducted Jan. 9-13.
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