Do genetics shape mental health trajectories around partnership transitions?

While the existing literature on the interplay between partnership dynamics and mental health has explored various moderating environmental factors, the influence of genetic propensity remains understudied. This is surprising due to the high share of variation in mental health that can be explained by genes. Investigating whether people with different genetic predispositions react differently to partnership transitions could add substantial knowledge to the research on partnership dynamics and mental health. Therefore, this study explores to what extent genetic propensity for depression impacts antidepressant (AD) purchasing up to five years before and five years after union formation and dissolution. It draws on two partly competing gene-environment interaction models: the diathesis stress model, which assumes that individuals with a greater genetic propensity for depression are more affected by union dissolution; and the differential susceptibility model, which assumes a stronger impact of union dissolution as well as union formation on these individuals. We follow the genotyped sample of the FINRISK rounds 1992–2012 and the Health 2000 and 2011 surveys with linkage to Finnish register data from 1997 to 2019. We use individual fixed effects models, analyzing individuals who have experienced union formation (N=7,888) or union dissolution (N=7,375). The results suggest that only women with different genetic endowments had different mental health reactions following a union formation. More specifically, only women with high genetic propensity for depression showed an increase in AD purchasing probability following union formation. The results did not show any gene-environment interaction following union dissolution. However, in the period three to five years before a union dissolution, individuals with high genetic propensity for depression were particularly vulnerable, as the changes in AD purchasing probability were larger for them than for the group with low genetic propensity. These findings partly support the diathesis stress model.