Okay, I made an account specifically to reply to this thread, as the information posted here about DXM is VERY innaccurate.
As a long term user of DXM in high doses, I've studied, and experienced far more than all of you most likely have. The truth about DXM is that it's virtually harmless if abused PROPERLY. We're talking long term effects, here. The damage it does to your system is about as minimal as eating mushrooms or taking acid, which have also been proven to be virtually harmless in medical studies and by people that have used these substances thousands of times with no negative effects, save for depleted brain cells (and keep in mind, you've got billions of these, you kill brain cells just getting through the day, they were meant to be burned off.)
As for the permanent mental effects, you can expect next to none unless you're mentally unstable to begin with, and nothing of extreme concern will come about with an 800MG dose of Dextromethorphan, or lower, anyway (I do not advise a higher dose than this as it CAN cause health complications in some users.)
I advise all of you not to experiment with this, But if you do, make sure that the only ACTIVE INGREDIENT listed on the box is Dextromethorphan HBr, or Dextromethorphan polistirex.
The effects can be unpleasent though, kids, so be careful.