Objective — To determine if physician warnings to psychiatric patients alter the subsequent frequency of a motor vehicle crash. A secondary objective was to determine if physician warnings change the subsequent frequency of psychiatric hospitalization.
Methods — Exposure crossover design of 23,145 psychiatric patients diagnosed with ICD-9 schizophrenia (code 295), mood disorder (296), personality disorder (301), or substance use disorder (303, 304) and warned by their physician about driving safety between April 1, 2006, and March 31, 2011. Each patient was followed for 4 years before the warning and 1 year after the warning. Patients living outside the region or lacking a valid health card number were excluded.
Results — Patients' motor vehicle crash frequency decreased from 11.78 to 8.17 events per 1,000 patients per year after a physician warning, which corresponded to a relative risk of 0.69 (95% CI, 0.59-0.81; P < .001). Psychiatric hospitalization frequency increased from 147 to 289 events per 1,000 patients per year corresponding to a relative risk of 1.97 (95% CI, 1.91-2.03; P < .001).
Conclusions — Physician warnings are associated with a subsequent decreased frequency of motor vehicle crashes and increased frequency of psychiatric hospitalization. This result suggests that physician warnings are an effective intervention for reducing road trauma but need to be weighed against potential adverse psychiatric health.