Polar day and polar night: month of year and time of day and the use of physical and pharmacological restraint in a north Norwegian university psychiatric hospital.

All episodes of restraint in a Norwegian university psychiatric hospital during a five and a half-year period have been studied retrospectively. An examination of the protocols in which the use of restraint is noted reveals that patients' aggression and the subsequent use of restraint follows daily and seasonal rhythms. There is a daily peak with most use of restraint in the afternoon and early evening and a seasonal peak- with the most use of restraint in autumn. Patients' age and sex also influence the daily and seasonal patterns of restraint. It is suggested that the 24-hour patterns as well as the seasonal patterns of aggression and restraint result from the combined influence, in susceptible patients, of light-dark cycles and variations in life-events and the ward environment.