Objectives Mergers and acquisitions (M&A) activities are increasing and may negatively affect workers mental health. However, the impact of M&A on the risk of developing a mental disorder, rather than psychiatric symptoms, has not been investigated. The objectives of this study were to estimate and compare the 12-month incidence of depressive and anxiety disorders in workers who had and who had not experienced M&A in the last year.

Methods Employees aged 25 and 64 years old were randomly selected from the community and were followed for 1 year (n=3280). Questions about their experience in M&A in the past 12 months were asked. WHO's Composite International Diagnostic Interview–Auto 2.1 was used to assess depressive and anxiety disorders. The 12-month prevalence and 1-year incidence of mental disorders were estimated and compared in relation to M&A.

Results Participants who were exposed to M&A had a significant higher 1-year incidence of generalised anxiety disorder (GAD) (6.7%) than the unexposed (2.4%). They were not different in the incidence of major depressive disorder. The exposed participants were 2.8 times more likely to have had a GAD than others and were about 2.4 times more likely to have developed any anxiety disorders over 1 year.

Conclusions M&A may lead to increased risk of GAD, which may, in return, evolve into major depression. Governments, employers and health professionals should be aware of this and work out plans to reduce the negative health outcomes of M&A.