>> the concentration of thc in marijuana today is 30,40% in a typical smoke marijuana versus 3 or 4% thc concentration of 60s and 70s. >> reporter: other drugs including alcohol and nicotine have higher addiction rates. but there is serious concern among those in the substance abuse field that colorado's new marijuana law will substantially increase the number of marijuana addicts. >> i think we'll see more people using it on a consistent basis. >> reporter: but addiction isn't the only concern. 22-year-old stella blessing is also a successful graduate. she was addicteded to crack, meth and heroin. but she preceded that with what the therapists here say are the typical gateway drugs of alcohol and marijuana. >> how often did you use marijuana? >> the first time i smoked marijuana i was 14. and i used it constantly throughout my other addictions. >> reporter: stella, brian and