Doctors should assess whether seniors who show psychiatric symptoms or are prescribed antidepressants and sedatives for dementia are fit to drive, Canadian researchers say.

In the October issue of the Journal of the American Geriatrics Society, researchers reviewed data on use of the medications and motor vehicle collisions in 210,550 people aged 65 and older with dementia from April 1997 to March 2005 in Ontario.

"Patients on psychotropic medications — antipsychotics, benzodiazepines or antidepressants — were at a significantly greater risk of a motor vehicle collision by approximately 50 per cent," said the study's lead investigator, Dr. Mark Rapoport, a  psychiatrist at Toronto's Sunnybrook Health Sciences Centre and a psychiatry professor at the University of Toronto.

"The emergence of psychiatric symptoms or the prescription of psychotropic medications for patients with dementia should prompt physicians to evaluate the impact on road safety," the researchers concluded in letter published by the journal.

About 40,500 of the patients with dementia, or 19 per cent, had active driver's licences. Of those, 9,763 or 24 per cent had been involved in at least one vehicle collision, the researchers found.

Antipsychotic drugs were associated with the highest risk of collision, 3.35 times higher, compared with people who took steroid creams or antifungal agents as a control.

The research team members represented Sunnybrook, the Ottawa Hospital, Baycrest Centre for Geriatric Care and the Institute of Clinical Evaluative Sciences.

The risk of antidepressants was intermediate at 1.824 times higher than a placebo, while benzodiazepines showed a risk 1.116 times higher.

"The greater risk of a motor vehicle collision may reflect the underlying indication for the prescriptions, rather than the pharmacological properties of the drugs themselves," said Dr. Nathan Herrmann, a co-author of the study and a geriatric psychiatrist at Sunnybrook.