Probiotic Research for Mental Health in Adult Volunteers

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.

Inclusion Criteria: * 18-30 years of age * Native-level Danish language skills * No current psychiatric illness, confirmed with the Presence State Examination (PSE) and the Standardized Assessment of Personality (SAPAS) * No previous history of severe psychiatric illness, including bipolar disorder, recurrent unipolar depression, psychosis spectrum disorders, personality disorders, autism spectrum disorders, or attention deficit (hyperactivity) disorder (ADHD/ADD), confirmed with PSE and SAPAS. Participants may still be included if they have a history of a single depressive episode, or have experienced symptoms of anxiety, stress, or burnout more than 6 months ago. Exclusion Criteria: * Recent use of probiotics (within the past 4 weeks) * Use of antibiotics within the past 3 months * Smoking, chewable tobacco, vaping, or use of other nicotine products * Neurological disorders (including dementia) * Use of psychotropic medication within the previous 6 months, including: * Anxiolytics * Antidepressants * Antipsychotics * Anticonvulsants * Centrally acting corticosteroids * Opioid pain relievers * Hypnotics * Prescribed sleep medications or herbal sleep aids (e.g., valerian) * Dyslexia * Severe physical illness, including: * Cardiovascular disease * Diabetes * Gastrointestinal pathology (e.g., colon cancer, colitis, Crohn's disease) * Gynecological pathology (e.g., endometriosis) * Urologic pathology (e.g., prostate cancer) * Severely immunocompromised status, including: * HIV positive * Being a transplant recipient * Use of anti-rejection medication * Use of steroids for more than 30 days * Chemotherapy or radiotherapy within the last year * Current alcohol or substance abuse disorder * Previous severe head trauma * History of epilepsy * Pregnancy or breastfeeding * Known allergy to any component of the test product * Participation in a clinical study with another investigational product within 60 days before screening, or plans to participate in another study during the study period * Significant change in dietary habits within the previous 4 weeks (e.g., starting a fibre-enriched diet) * Planned major changes in diet or exercise habits during the study period * Current pregnancy