or cold didn't detour. the line in the hundreds all day long. what does today feel like? >> freedom. >> reporter: with freedom comes responsibility. signs are everywhere, the dos and don'ts of pot, illegal for under 21 to light up, public health officials fear abuse. at greatest risk, kids. >> over half of the admissions for addiction in this state in kids under 15 and teenagers are from marijuana. >> reporter: and drivers can get busted. the legal limit 5 nanograms of thc in your blood. i don't smoke. >> right. >> reporter: but if i have one puff of a marijuana cigarette, will that put me over the five nanno gram limit? >> yes. >> reporter: for how long? >> after -- by two hours, it will probably be gone. >> reporter: thc dissipates to lower levels relatively fast,