Up until now it hasn't put a dent in the marijuana black market. Because of dispensary overhead and taxes, legal marijuana is pretty expensive. Most everybody I know that smokes (and I know quite a few) still buy it off of the black market simply because of cost.

With that said. I read an article just a day or two ago but can't seem to find it now...anyway, it said that the cost of legal weed in CO is dropping fast and it is now becoming cost effective to buy at a dispensary over the black market. Only time will tell if it begins to have an effect on cartels.