CO Governor John Hickenlooper provides more detail in an interview with his thoughts on cannabis legalization in his state, and how he hasn't seen anything negative regarding an increase in "kid usage" which was one of his greatest worries.
As the Governor explains, people to his surprise have reacted in a much more responsible fashion than he had originally envisioned.
Each of the states need to continue to watch the effects of usage after legalization. For legal professional operations, it is incumbent upon everyone to make sure the product is safe, and that there are the necessary protections against under-age access, and that there is not illegal diversion of product.
As described, the population continues to overwhelming support legalization and decriminalization, and only upon such success we the proper research be able to be conducted on where and how cannabis is medicinally beneficial.