….marijuana now' legal in colorado :) , page-124

JUSTIS

I don't think that's altogether true about Marijuana not having harmful chemicals, in fact Im pretty sure a lot of the gene spliced and hydro grown stuff does.
It most certainly has a high tar and resin content that goes into youre lungs.

Just like anything else if you want to make sure you are eating or using pure stuff then buy it from a reputable organic dealer, or just grow the stuff yourself.