Make sure if you're going to recreationally take DXM that the product you're taking it from does not contain any other medicine... this is the real safety issue. certain over the counter pain killers, anti-histamines, or expectorants, can cause a whole array of unwanted side effects. One notable example of this is coricidin cough and cold making people's sinuses so dry that they would bleed from their tear ducts. DXM by itself may cause your stomach to hurt, thus leading to vomit, although after you barf the pain sometimes goes away.

My two favorite sources for information about drugs (recreational or otherwise) are http://www.erowid.org and bluelight.ru
Both websites contain vast amounts of information pertaining to the recreational use of DXM.