Although dangers exist for marijuana users of all ages, risk is greatest for the young. For them, the impact of marijuana on learning is critical, and pot often proves pivotal in the failure to master vital interpersonal coping skills or make appropriate life-style choices. Thus, marijuana can inhibit maturity. Another concern is marijuana’s role as a "gateway drug," which makes subsequent use of more potent and disabling substances more likely. The Center on Addiction and Substance Abuse at Columbia University found adolescents who smoke pot 85 times more likely to use cocaine than their non–pot smoking peers. And 60 percent of youngsters who use marijuana before they turn 15 later go on to use cocaine. But many teens encounter serious trouble well short of the "gateway." Marijuana is, by itself, a high-risk substance for adolescents. More than adults, they are likely to be victims of automobile accidents caused by marijuana’s impact on judgment and perception. Casual sex, prompted by compromised judgment or marijuana’s disinhibiting effects, leaves them vulnerable not only to unwanted pregnancy but also to sexually transmitted diseases (STDs).