Voters in Colorado and Washington state will decide in November whether to legalize marijuana for recreational use under their state laws, despite opposition from the federal government, which considers pot an illegal narcotic liable to be abused.
If the measures are approved, the states would be the first in the nation to allow recreational use of the drug.
A total of 16 states and the District of Columbia allow medical marijuana. Following are details on some of those states and others where cannabis has emerged as a political issue:
Colorado voters approved medical marijuana in 2000, but dispensaries did not begin opening in large numbers until 2009, after which legislators passed measures to regulate marijuana's cultivation and production.
The state currently has one of the most extensive systems in the United States for regulating medical pot, and it is the only state where officials explicitly allow for-profit sales.
Voters will decide in November whether to legalize recreational use of the drug, giving adults 21 and older the right to possess up to an ounce of pot or six plants for cultivation. Colorado voters rejected a measure to legalize small amounts of cannabis in 2006.
Federal authorities have warned dispensaries located near schools in the state to close, but have so far treated Colorado with a light touch.
Washington state voters legalized medical marijuana in 1998 and, as in Colorado, voters will decide in November whether to legalize recreational use of the drug.
Governor Chris Gregoire last year vetoed a bill to establish state licensing for the cultivation and distribution of medical marijuana, saying she did not want to put state employees at risk of federal prosecution.
The two U.S. attorneys for Washington state had earlier sent the governor a letter saying state employees who might get involved in licensing medical pot "would not be immune from liability" under the federal Controlled Substances Act.
Despite the lack of state rules, Washington state has dispensaries that are regulated at the local level.
Arizona voters approved a measure in 2010 to allow medical marijuana, and state officials say they will accept applications for medical pot dispensaries from May 14 through May 25.
But Republican Governor Jan Brewer signed into law in April a bill to ban medical marijuana from being used on state university campuses, in a move supporters said was aimed to protect federal funding for higher education, which they said was at threat if medical marijuana was allowed in state schools.
California voters passed a ballot measure in 1996 that made the state the first in the nation to approve medical marijuana. But there are few uniform rules, as state law gives authority to local officials to regulate the industry.
California voters rejected an initiative to legalize possession and cultivation of small amounts of marijuana for recreational use in 2010, partly over concerns about how production and sale of the drug would be regulated.
U.S. government prosecutors announced a crackdown in October 2011 on what they called California's massive commercial marijuana trade, including medical pot dispensaries they said were often fronts for illegal for-profit drug distribution.
They outlined a range of actions including civil forfeiture lawsuits against property owners involved in drug trafficking, written warnings to landlords of storefronts illegally selling pot, and criminal prosecution of other cannabis offenses.
Earlier this month, U.S. agents raided Oaksterdam University, a cannabis industry college in Oakland that is widely known as the "Princeton of Pot."
Montana voters approved medical pot in 2004, before lawmakers approved a sweeping revision of the medical pot measure last year in response to concerns about illicit pot abuse among the state's growing rolls of cannabis patients.
Montana dispensaries were shut down as a result of the new law combined with raids and prosecution by federal authorities.
Lawmakers in New Jersey approved medical marijuana in 2010, but state officials have been slow to implement the law. Governor Chris Christie has expressed concern that medical marijuana could lead to illicit abuse of the drug that he said had occurred in other states.
To date, the state system has not allowed any patients to access medical pot, said Tamar Todd, an attorney with the Drug Policy Alliance who focuses on marijuana issues.
But state officials say they are working to start the program, which is complicated by federal opposition, and that they plan to allow six nonprofit groups to each operate a medical cannabis treatment center.
Organizers of a campaign to legalize marijuana for recreational use in Missouri are seeking to collect 144,000 signatures to meet a May 6 deadline to put the question before voters in November, said John Payne, one of the campaign directors for Show Me Cannabis Missouri.
So far, Michigan is the only state in the Midwest to allow medical marijuana. No Southern state has approved it.
Signature gatherers are seeking to get two pot legalization measures on the November ballot in Oregon, where medical cannabis is allowed under a measure approved by voters in 1998.
The deadline is July 6 for each campaign to turn in signatures to state officials to qualify for the ballot.
(Reporting By Alex Dobuzinskis; Editing by Cynthia Osterman)