A new study finds that while teen boys are more likely to smoke pot than teen girls are, the girls are quicker to become habitual smokers after their first hit. The study also uncovered racial differences: white girls were more likely to get stoned than African-American or Asian-American girls, but African-American and Hispanic boys were more likely than white ones. And participating in extracurricular activities lowered marijuana use for all teens, but the effect was biggest in girls.