Mental health conditions, including both mental disorders and mental distress, are common among adults, including among the working population. Although work generally promotes health, previous research indicates that several factors in the work environment may contribute to poor mental health. This thesis aims to examine whether workplace bullying, defined as repeated exposure to negative acts at work over a prolonged period, contributes to the occurrence of depression and anxiety among individuals of working age. To address this aim, longitudinal survey and register data from Sweden and Denmark are used.

The first paper of the thesis, Paper I, aimed to assess the theoretical and psychometric properties of a measure of workplace bullying used in Papers II-IV. The results showed that the measure captured theoretically grounded experiences of workplace bullying and that it overlapped satisfactorily with established measures of workplace bullying, thereby supporting its validity and justifying its use in the subsequent papers of the thesis.

Paper II examined the association between workplace bullying and anxiety symptoms, as well as whether good leadership quality could mitigate anxiety following exposure to bullying. When exposed individuals were compared with non-exposed individuals, the results indicated a bidirectional association. Exposure to workplace bullying was prospectively associated with an increased risk of higher anxiety, while higher initial anxiety increased the risk of subsequent exposure to workplace bullying. However, in analyses accounting for within-individual changes in bullying status, only immediate, but not long-term, changes in anxiety were observed, and no reverse association was found. Furthermore, no evidence was found of leadership quality moderating these associations.

Paper III examined the association between workplace bullying and sickness absence due to depressive and anxiety disorders, also considering bidirectional associations. The results indicated that individuals exposed to workplace bullying had an increased risk of sickness absence during the subsequent two years compared with non-exposed individuals. However, no clear evidence was found that such sickness absence increased the risk of later exposure to workplace bullying.

The fourth paper of the thesis, Paper IV, examined whether workplace bullying was associated with an increased risk of treatment with psychotropic medication. The analysis was restricted to individuals without prior exposure to workplace bullying and without a recent history of psychotropic medication use. The results suggested an increased risk of initiating psychotropic treatment during the subsequent two years among exposed individuals, with the risk of initiating treatment with antidepressants being particularly pronounced.

In conclusion, the findings of the studies included in this thesis indicate that workplace bullying constitutes a risk factor for depression and anxiety. The consistency of the observed associations, even after adjustment for sociodemographic factors, prior mental health conditions, and other work environment factors, strengthens the credibility of the results. These findings underscore the importance of preventive efforts against workplace bullying and of ensuring that exposed individuals receive adequate and timely support to reduce the risk of subsequent mental health conditions.