While this study in has a very small sample size, it nonetheless presents an interesting point, and one that needs to be taken into account when attempting to limit the use of illicit drugs (and the illicit use of licit drugs) by teens.
…these teens differentiated themselves from recreational users and positioned their use of marijuana for relief by emphasizing their inability to find other ways to deal with their health problems, the sophisticated ways in which they titrated their intake, and the benefits that they experienced…Marijuana is perceived by some teens to be the only available alternative for teens experiencing difficult health problems when medical treatments have failed or when they lack access to appropriate health care.
One of the common reasons for use of illicit drugs is self-medication. Certainly a completely different approach would be needed in these individuals than in recreational users. Likely these folks present a different set of challenges.