A marijuana plant grows in California's Shasta-Trinity National Forest. This plant is part of an illegal growing operation by highly organized drug cartels that take advantage of the forests' thick canopy to help hide their operations. Eric Westervelt/NPR hide caption
Come Jan. 1 it will be legal to smoke recreational marijuana in Illinois. But housing authorities say it will remain prohibited in public housing. Susan Montoya Bryan/AP hide caption
Workers prune marijuana plants at a Clever Leaves greenhouse in Pesca, Colombia. The company employs over 450 people. Courtesy of Clever Leaves hide caption
University of Pittsburgh researchers developed a prototype device that can measure the amount of THC in a person's breath. Courtesy of the University of Pittsburgh hide caption
Marijuana use is risky for teens and pregnant women and can be habit-forming, says the U.S. surgeon general. Jane Khomi/Getty Images hide caption
U.S. officers found nearly four tons of marijuana in a shipment of peppers in San Diego. U.S. Customs and Border Protection hide caption
A Court of Appeals ruled that "the odor of marijuana coupled with possession of what is clearly less than ten grams ... does not grant officers probable cause" to search and arrest a person. Gerald Herbert/AP hide caption
Cannabidiol, or CBD, is a compound that can be extracted from marijuana or from hemp. It doesn't get people high because it doesn't contain THC, the psychoactive component of the cannabis plant. Getty Images hide caption
Studies have shown that the levels of THC, the main psychoactive compound in pot, rose dramatically in the U.S. from 1995 to 2017. David McNew/Getty Images hide caption
A bipartisan group of attorneys general is urging Congress to pass legislation that would make it easier for banks to handle money involved in the legal cannabis industry. Brennan Linsley/AP hide caption
Cannabis: The Illegalization of Weed in America, by Box Brown First Second hide caption
Research shows a link between marijuana use and psychosis. Kirill Vasikev/EyeEm/Getty Images hide caption
Marijuana plants grow in a marijuana cultivation facility on July 6, 2017 in Las Vegas, Nevada. Ethan Miller/Getty Images hide caption
A vendor points to a selection of cannabis strains for sale during a 2018 marijuana festival in California. Richard Vogel/AP hide caption
Baltimore State's Attorney Marilyn Mosby walks through a city neighborhood on August 24, 2016. Larry French/Getty Images hide caption