Personality traits of romantic partners may be part of the puzzle of how romantic relationships are related to mental health. We investigated the role of narcissistic admiration and rivalry in this context. Positive associations of admiration and negative associations of rivalry with the mental health of individuals and their partners were hypothesized. Furthermore, we expected admiration to be particularly relevant for the narcissist’s mental health and rivalry to matter more for the partner. Actor-partner interdependence models and Bayesian inference methods were used (n = 7438 couples). Hypotheses and methods were pre-registered. Contrary to expectations, the results only supported the hypotheses concerning actor effects. Most partner effects were miniscule, with the exception of the effect of male rivalry on female mental health. While controlling for extraversion and agreeableness reduced and partly reversed the initial effects of narcissism, an exploratory analysis suggested that these personality factors should be considered as mediators and that most partner effects of admiration and rivalry on mental health may be cases of indirect-only mediation, with extraversion and agreeableness acting as process variables. While replications are needed, the findings suggest that the question posed in the title may be answered with “not that much, apparently”
