This study is being conducted to better understand depression in adolescents and young adults and to explore whether probiotics can improve brain health, gut bacteria, and mental health outcomes in people already taking antidepressant medication.

You may be eligible for this study if you meet the following criteria.

Inclusion Criteria:

• Ages 15–24
• Diagnosed with depression
• Taking an SSRI antidepressant (such as Zoloft, Prozac, or Lexapro) for at least 8 weeks
• Under the care of a primary care or mental health provider
• Able to complete study visits and online questionnaires in English

Exclusion Criteria:

• Other major psychiatric disorders (except anxiety or ADHD if stable)
• Recent use of antibiotics, probiotics, or certain supplements
• High alcohol use or tobacco use
• Any condition that would make MRI unsafe
• Pregnancy or plans to become pregnant during the study

This study lasts about 8 weeks. During this time, participants take a probiotic or placebo every day and complete a few study visits and online activities.

In-Lab Activities:

Participants will come to UCSF Mission Bay for 2 visits—one at the start and one at the end of the study. At these visits, they may complete interviews, questionnaires, and brain scans (MRI). They will also provide saliva and stool samples. These visits help researchers understand changes in the brain and gut over time. No video or audio recording is used for personal conversations.

At-Home Activities:

Between visits, participants take a probiotic or placebo twice a day for 8 weeks. They also complete online questionnaires and may use Zoom for remote check-ins. Some simple surveys may ask about mood, health, and daily experiences. All responses are kept private and used only for research.

Participants may receive up to $200 for completing the full study. Parking costs are also covered for in-person visits. 

There is no cost for you to participate in our research study.