Seasonal patterns of initiating antidepressant therapy in general practice in the Netherlands during 2002-2007

Studies on seasonality in antidepressant prescribing showed prescribing peaks during autumn and winter. Since then, new antidepressants have become available and indications have broadened, possibly contributing to a change in prescribing practices. This study investigates seasonal patterns of initiating antidepressant use in general practice during 2002-2007 in the Netherlands.

Data were obtained from the Netherlands Information Network of General Practice. The study population was composed of adult patients initiating antidepressant use from 21 December 2001 to 20 December 2007, with no antidepressant use during at least two years prior to initiation. Seasonal distribution of initiating antidepressant use was investigated for the four seasons. The difference in frequency of initiating use between the seasons, normalized for general practice contacts, was tested using Chi-square testing.

The majority of the study population (N=16,289) was female (64.0%) with a mean age (standard deviation (SD)) of 50.5 (18.0) years. Significant seasonal variation (p<0.01) was found in initiation of antidepressant use, with about 5-35% more patients initiating use during winter than summer. Significant (p<0.01) seasonality of initiating antidepressant use was seen in all patient groups, except within age groups 18-30 years and >60 years.

Our study investigated only general practitioner prescribing thus additional prescriptions from psychiatrists are missed.

The seasonal influence on initiation of antidepressant drug use has not changed with the introduction of the newer antidepressants and is in line with seasonality of depression onset, with most patients initiating use during the winter and fewest during the summer.