Background Drug use has increased over recent decades, and is especially great among women and among people with mental health problems. To take advantage of the full potential of drugs and to avoid drug-related problems, drug prescription needs to be correct and the drugs need to be taken according to the prescribed regimens. Research on drug utilization is thus important to the public health.

Aim To study the influence of gender and depression on drug utilization, prescription of drugs and self-reported use of drugs, i.e. adherence.

Methods The thesis included two population-based questionnaires and data from the Swedish Prescribed Drug Register (SPDR) covering Swedish citizens 18-84 years. The questionnaire in Study I and II included items on prescription drug use and adherence to treatment regimens; Study II also included the Hospital Anxiety and Depression Scale (HADS) for self-estimation of anxiety/depression. The questionnaire in Study III included the HADS and data from the SPDR on prescribed antidepressants. Study IV included data from the SPDR on all types of prescribed drugs.

Results Men and women differed in non-adherent behaviours and reasons for non-adherence, for example, men were more likely to report forgetting to take the drug, while women were more likely to report adverse drug reactions (ADRs) as a reason for non-adherence. Further, both anxiety and depression were associated with non-adherence and with ADRs as a reason for non-adherence. In addition, men reported depression to a greater extent than women did but used antidepressants to a lesser extent, while women used antidepressants without reporting depression more often than men did, which may be a sign of under-treatment among men and over-treatment among women. Moreover, the associations between antidepressants and other types of drugs differed by gender; they were often specific, or stronger, in women than in men, which may be a sign of a gender difference in comorbidity between depression and other conditions.

Conclusions Although the cross-sectional study design prevented confirmation of causality, the thesis found that gender and depression influence both prescription of drugs and adherence, and are thus important to pay attention to in clinical practice as well as research.