. >> joel vargas started smoking when he was just 13.15 he was smoking more than a dozen times a day. he stopped skateboarding. he even dropped out of school. >> i like getting high. i need to get high because my brain is telling me. >> adolescents, starting about age 13 have a pretty mature brain reward center. so they can experience rewards and pleasures the same way adults can, but the problem with that is that their prefrontal cortex, which helps people think ahead, control their impulses, that's not fully developed until age 24. that explains why adolescents are much more vulnerable. >> there's something else that addiction experts believe is likely happening in the brain. when you smoke pot, the feel-good chemicals that make up marijuana called cannabinoids, remember them? they cause your brain to stop producing its own natural cannabinoids. when you stop smoking, you have no feel good cannabinoids of your own. until your body kick starts production, you feel lousy, so many people smoke again to feel better. and today's marijuana c

. >> it happened to joel vargas. ter a couple years of smoking daily, joel eventually ended up in rehab. where he faced mild withdrawal symptoms. like irritability. insomnia. nausea. >> it certainly isn't anything nearly as dangerous as abrupt discontinuation of alcohol. for someone like joel, it is about learning new behavior, more than the physiological tolerance or withdrawal issues. >> joel's been clean now for six months. but these kinds of risks, they don't scare off charlotte figi's parents. >> people ask us that a lot. lining how did you make that decision? it wasn't a decision. >> it wasn't a decision. >> it was the next viable option. >> and some would say, a radical option. marijuana for a 5-year-old. but it was an option they hoped would change her life forever. >> hi, baby. >> when we come back, matt and paige figi, finally give their charlotte, marijuana. the results are shocking. [ male announcer ] the new new york is open. open to innovation. open to ambition. open to bold ideas. that's why new york ha