Double major questions

I was wondering if it was possible to double major in toxicology with either chemistry or biology. I went to an academic advisor who told me double majors have to be a listed program on the major's university catalogue page and I'd have to do a minor. But, I've also heard that you just have to do 30 credits that don't overlap. So... ?

Also how would a minor work if you were in two major programs? Does it get applied to both, or just one? Could you even get a minor?