AbstractNostalgic reverie (i.e. sentimental longing) has received increased attention as a predictor of health and well‐being, but only a handful of reviews have summarized this literature. The available reviews (Dementia: The International Journal of Social Research and Practice, 19, 2020, 330; Intimations of nostalgia: Multidisciplinary explorations of an enduring emotion, Bristol University Press, 2022) left a critical gap in explicating the function of nostalgia among people engaged in unhealthy behaviour. In the current systematic review and narrative analysis, we sought to answer whether and under what conditions emotion serves to help or hinder people engaged in unhealthy behaviours in terms of taking action to change. We identified 14 studies and categorized them into two themes. In Theme I, nostalgising about a time in one's life when one was healthier motivated both readiness to change and action to change unhealthy behaviour. In Theme II, nostalgizing about the perceived benefits of engaging in unhealthy behaviour (e.g. social connectedness related to drinking) was associated with the continuance or acceleration of the unhealthy behaviour. This review highlights not only the presence of a link between nostalgia and unhealthy behaviour but also that the content of one's nostalgising matters for understanding whether the unhealthy behaviour is undermined or bolstered.