The goal of this randomized controlled trial is to learn if supplementation with the probiotic Lactobacillus reuteri DSM 17938 can reduce levels of trait and state perceived stress, anxiety, and depressive symptoms compared to a placebo in a population of stressed adults ages 18-45. This study also investigates several evidence-based moderators of treatment effects, evaluates whether the probiotic caused side effects, and evaluates whether effects endured at 1-month post-supplementation.

Inclusion Criteria:

• age 18 - 45
• scoring 14+ on the perceived stress scale-10 indicating medium stress or higher
• ability to provide informed consent
• willingness not to take probiotic supplements (pills, tablets, oils, etc.) other than the product provided in the clinical study until all study procedures are completed
• own a smartphone and are willing to receive study materials and complete study procedures by text

Exclusion Criteria:

• a history of gastrointestinal discomfort or surgery, urinary incontinence, cancer, toxic shock syndrome, frequent diarrhea, vital signs outside of the acceptable range (i.e., blood pressure >160/100, oral temperature >100°F, pulse >100), heart disease, heart attack, lung/respiratory disease, any pulmonary, cardiovascular, gastrointestinal, hepatic or renal functional abnormality (i.e. a medical diagnosis related to lungs, heart, stomach/intestines, liver, or kidneys), HIV, Hepatitis B, Hepatitis C, bipolar disorder, psychosis, or confirmed or suspected immunosuppression or immunodeficiency
• current (past month) alcohol or substance abuse or dependence (score of 2+ on the UNCOPE)
• consistent (e.g., 5x/week or greater) probiotic supplementation within the last month, including probiotic food products such as yogurt
• receiving antibiotics within the last month
• receiving medications that interfere with gut motility (opiates, loperamide, stool softeners)
• use of systemic antibiotics, antifungals, antivirals, or antiparasitics (intravenous, intramuscular, or oral)
• use of oral, intravenous, intramuscular, nasal or inhaled corticosteroids
• use of cytokines or cytokine inhibitors
• use of methotrexate or immunosuppressive cytotoxic agents
• receiving immunosuppressive drugs/medications or treatment including antineoplastic therapy, post-transplantation immunosuppressive therapy, and/or radiation therapy
• participation in conflicting interventional research protocol
• unstable dietary history as defined by major changes in diet during the previous month, where the subject has eliminated or significantly increased a major food group in their diet
• female who is pregnant or lactating or reports expecting to get pregnant during the course of the study
• currently involved in the criminal justice system as a prisoner or ward of the state

Deidentified individual participant data (IPD) will be shared with other researchers in our lab to conduct secondary analyses. Data sharing will ensure protection of participant confidentiality.

Beginning late summer/early fall of 2024 with no end date

Faculty advisor who oversaw the initial trial is supervising another graduate student to use the data to address research questions outlined in the IRB-approved protocol, in addition to some secondary analyses.