With hormonal contraception becoming more and more widespread, it is important to understand its effects on body and brain. While there are a handful of studies on oral contraceptives (OC), they mostly focus on the bodily effects. A few studies have shown effects on the brain, specifically on stress reactivity, emotion regulation and the appearance of mental disorders. Studies on the hormonal intra-uterine device (LNG-IUS) are even scarcer. In our proposed study, we want to better understand the stress reactivity and how it can be altered by the use of hormonal contraceptives. Comprehending the mechanisms of stress reactivity is of utmost importance to understand the emergence of stress-related mental disorders like depression and anxiety, especially in the context of hormonal contraception, as the two endocrine systems – the hypothalamic-pituitary-adrenal axis (HPA) and the hypothalamo-pituitary-gonadal axis (HPG) – are in interaction. As of yet, there is only one study that focused on the interplay between LNG-IUS and the stress reactivity: while OC users tend to show a blunted cortisol reaction compared to naturally cycling women, LNG-IUS users seem to have a potentiated reaction. We want to investigate stress reactivity in four groups of women – naturally cycling women, established OC users and LNG-IUS users/starters – and how it can be altered by the use vs. start of hormonal contraceptives in a longitudinal study design. To carefully investigate the effect of LNG-IUS and its stability over time, we will measure the stress reactivity (subjective, hormonal and behavioural) of all women several times. By doing so, we will be able to investigate a) how the stress reaction is modulated by LNG-IUS start, and b) how individual stress reactions evolve. Thus this project has an enormous societal relevancy, as women worldwide can make a more informed choice as to which contraceptive method they want to choose.