Nurses who worked in hospitals that were understaffed, had inadequate medical resources and who had high rates of overtime were most likely to report that patients had been the victims of medication mistakes, a survey finds.

The report, published Wednesday by Statistics Canada, shows that medication mistakes are quite common in Canadian hospitals.

Nineteen per cent of registered nurses said that in the year before the survey, medication errors that they had witnessed had occurred "occasionally" or "frequently."

This type of error was significantly related to overtime work by nurses. When nurses worked overtime, 22 per cent reported medication mistakes, versus 14 per cent of those with regular shifts.

Fifty-three thousand nurses, or 38 per cent of those surveyed, said they usually worked 40 or more hours per week, with 45 per cent reporting that they usually work a 12-hour shift.

Working relations between doctors and nurses played a big part in medication mistakes. When conditions were poor, 27 per cent of nurses reported medication errors. However, when relations were cordial, only 12 per cent reported drug mistakes.

Low job security also played a part in the number of medication mistakes. Thirty per cent of nurses reported this type of mistake in hospitals where job security was low compared to 19 per cent with better job security.

And dissatisfaction with the job also played a role. Twenty-eight per cent of nurses who said they were unhappy in their jobs reported medication mistakes versus 18 per cent who said they were happy.

The medication error rate was not affected by the level of nursing education, the number of years as a nurse or general health, according to the study.

"In the view of many Canadian nurses, the restructuring of hospitals and downsizing of the nursing workforce that has taken place since the early 1990s has had a major impact on the quality of patient care," reads the study. "It is hoped that this research will inform initiatives aimed at reducing risks to patient safety in Canadian hospitals."

The survey, conducted by the Canadian Institute for Health Information and Health Canada, took place between October 2005 and January 2006 and involved 19,000 nurses.