While frequent use of dextromethorphan does not appear to lead to physical withdrawals it definately has the potential to cause a psychological addiction. From my personal experience I would estimate between 50 - 75% of the people I know who have used DXM did so days in a row for weeks at a time and found it hard to quit. Many of them also suffered some kind of mental distortion or delerium lasting several weeks since their last use.

Of course it depends where you live, what kind of morons you hang out with etc but I've seen more people have problems with DXM abuse than all other drugs. Likely due to its low price and availability.