The rapid change matches an increase in usage - in the new poll, nearly half of Americans report trying marijuana at some point in their lifetime (48 percent), up eight points since 2010 and also a record high. More people who have smoked in the past year say it was "just for fun" than any medical issue (47 vs. 30 percent), while 23 percent say they smoked for both reasons.
The overall shift in support is driven by younger Americans who overwhelmingly support legalization, with nearly two-thirds of people born since 1980 (between ages 18 and 32) saying marijuana should be legal (65 percent). Baby Boomers and Generation Xers have become far more supportive than in the early 1990s, with at least half of each now supporting legalization.
As public opinion has shifted, the politics of marijuana have become more complicated. Laws legalizing recreational marijuana use passed in Washington State and Colorado last year remain in limbo with the federal government's ban on production, possession and sale of the drug unchanged. Six in 10 Americans say federal laws should not be enforced in states that have decided to allow marijuana use.
Enforcement of federal laws has also been drawn into question, with Senator Rand Paul (R-Ky.) saying in March that people shouldn't go to jail for non-violent drug crimes such as marijuana. Wide majorities of Democrats and Republicans agree that government efforts to enforce marijuana laws cost more than they are worth.Most Republicans remain opposed to legalizing marijuana, while about six in 10 Democrats and independents say it should be legal.
Stigma and fear of marijuana have dropped sharply. Far fewer people see marijuana leading to harder drugs today (38 percent) than in the 1970s (60 percent), and only one in three say smoking marijuana is morally wrong (32 percent), down 18 points from 2006.
The poll was conducted March 13 to 17 among a random national sample of 1,501 adults ages 18 and over. The margin of error for overall results is plus or minus 2.9 percentage points. Results for the share of Americans smoking marijuana were based on a separate survey conducted in January.
Clement is a pollster with Capital Insight, the independent polling group of Washington Post Media. Capital Insight pollster Peyton M. Craighill contributed to this report.