[little jeremiah]

Where mj is legal, illegal drug grows increase. Including CO. Also, other drugs such as meth and heroin use increase too.

[NobleFree]

Where mj is legal, illegal drug grows increase.

It's quite likely that any such increase is largely if not entirely an effective relocation of the supply for nonlegalizing states - relocating either from those states or from abroad. One of the downsides of being among the first states to legalize.