 More than 30 years after the start of America s war on drugs, drugs are still readily available, and many teenagers are still curious about them. Curiosity leads to experimentation, but is experimentation okay? New research on that question proves that the answer is no. Experts say that for some kids, a single exposure to a single drug will be enough to change the adolescent brain forever. Frances Leslie is a developmental pharmacologist at the University of California, Irvine: "The parts of the brain that are actually in charge of stopping us seeking pleasure whenever we feel like it, our higher centers, our executive control centers that stop those impulsive urges - they may be stopped by early drug exposure." According to the National Institute on Drug Abuse, 46 percent of kids try marijuana by the twelfth grade. Fifty-four percent try cigarettes. And 77 million try alcohol. Experts call these "gateway drugs" because nearly every hardcore drug addict starts out by using these drugs first. But, experts say that if kids stay off these drugs until their mid-twenties, there s almost no chance they ll ever start. Watch "Gateway" to find out what parents can do.