This white paper underscores the urgency of addressing the dangers associated with nonmedical marijuana use, particularly for children and teens. Current evidence is more than sufficient to demonstrate that marijuana does not just provide a harmless high; it is an increasingly dangerous game of Russian roulette. Highlights of findings about teen marijuana use include: (1) from 1996 to 2006, the potency of marijuana increased by 175.0 percent; (2) from 1992 to 2006, there was a 188.1 percent increase in the proportion of treatment admissions for persons under age 18 who cited marijuana as their primary drug of abuse; (3) many teens are using marijuana more intensely than in the past with rates of daily marijuana use among 12th graders tripling from 1992 to 1999; (4) despite recent declines in teen marijuana use, in 2007 the percentage of teens who had ever used marijuana was 26.8 percent higher among 8th graders, 44.9 percent higher among 10th graders, and 28.2 percent higher among 12th graders than lows in 1992; (5) by 2007, a total of 10.7 million 9th to 12th graders had used marijuana; (6) marijuana use interferes with brain functions and has been linked to other mental health problems in young people; and (7) marijuana is the second most frequently detected psychoactive substance among drivers (alcohol is first) and is associated with impaired driving skills. This white paper, third in the series, is prompted by the alarming increase in the potency of marijuana, and in teen emergency room admissions, treatment admissions, and clinical diagnoses of marijuana abuse and dependence. To educate the country about the dangers of teen marijuana use, the national government and the public health community should mount a major public education campaign. Figures, appendixes A and B and references