It's the kind of thing opioids.com would have an article on. They also had one about proglumide that I read a while back, and that seems to work for some people in lowering tolerance. Proglumide might be something worth looking into, but I kind of doubt it has a dramatic effect if you have a high tolerance- would love for someone to prove me otherwise.

DXM does potentiate opiates a bit, in my experience it hasn't lowered tolerance (some people say it does, though). But it also changes the effects, a bit of a rougher feeling, a less clean opiate come-on, if you will.

-yawkaw