Certain studies have shown that chronic use of a dissociative can cause brain lesions, but that theory has been discredited over and over again with the use of DXM. There have been studies that have shown chronic use (over 500mg daily) have had little to no physically adverse effects, but that's a bit suspicious to me. Personally I can't find hard evidence to show that DXM itself has ANY negatives with light use... the negatives usually come from FUCKING IDIOTS taking DXM from sources that contain other active ingredients besides DXM. And yes, they are IGNORANT FUCKS. They are the ones who make DXM use so taboo, and they're also the ones who usually "hear about some drug that'll fuck you up" and take it without knowing how/why it fucks you up, and what bad things it can do to you. This is obvious because if they actually took the time to properly research a chemical, they wouldn't bother popping CCCs or drinking shit with guaifenesin, etc... they'd find out that CPM can kill you and guaifenesin will make you puke your brains out.