ColoradoChris HondrosGettyImages 

An man smokes marijuana during a pro-marijuana rally at Civic Center Park with the Colorado State Capitol Building in the background yesterday, April 20, 2010 in Denver, Colorado. April 20th has become a de facto holiday for marijuana advocates, with large gatherings and 'smoke outs' in many parts of the United States. Colorado, one of 14 states to allow use of medical marijuana, has experienced an explosion in marijuana dispensaries, trade shows and related businesses in the last year as marijuana use becomes more mainstream here. By Chris Hondros/Getty Images.

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