This randomized, double-blind, placebo-controlled pilot study will evaluate the effects of four weeks of supplementation with a probiotic on mental health in healthy adults aged 18-30 years. Participants will be randomized to receive either probiotic or placebo and will complete study assessments at baseline and end of intervention, and will complete a range of behavioral, physiological, and questionnaire-based assessments before and after the intervention. The primary objective is to assess the effect on emotional reactivity measured in a virtual reality scenario at the end of the intervention. This exploratory study is intended to generate data to inform future clinical research.