It would appear that less than 1% of the total number are investigated each year. However, over a number of years this becomes a cummulative number. I have personal knowledge that stress health professionals are subjected to (trauma they deal with daily, death, hours worked [16 hour days in many cases], etc.) plus the availability of medication adds to the problem. But I think the cummulative affect of nurses addicted to meds is a higher number than the medical community would have us believe.
It maybe neat to find out how many are smoking pot or crack...