I got a call a few weeks ago from a friend who's studying in Spain. Apparently he went to the chemist to get some cough syrup and was given something OTC and told to take three 15ml spoonfulls every so many hours (every three or four I think). Closer inspection of the bottle revealed that each millilitre contained 19mg of DXM, which would mean the chemist was suggesting he took 405mg three or four times a day at least. Unfortunately for him he didn't bother to check the bottle til much later in the day, having spent most of the afternoon lying sprawled on a park bench halfway between the chemists and his university tripping heavilly and thinking he was going to die but not being particularly concerned about it.
Apparently he'd been taking codeine without much regard for the dosage as well as another anti-tussive I forget the name of. He'd also been drinking (he's seldom sober), which would have sped up the onset of the DXM and explains the intensity he experienced. Apparently at the time he'd paid very little attention to what the active ingredient in the cough syrup was, and only realised what it was when he later cheked the bottle and remembered me mentioning it at some point. He was absolutely shitting himself on the come-up, not knowing why he was suddenly off his tits.