Does abusing dextromethorphan cough syrup create some permanent brain damage?

Yes. At high does, dxm can cause coma and if deep enough, respiratory depression could certainly lead to anoxia and permanent brain injury. Deaths have also been associated with dxm overdose and certainly is a permanent condition. Much more on the subject at: http://www.Webmd.Com/parenting/teen-abuse-cough-medicine-9/teens-and-dxm-drug-abuse?Page=1.