Probiotic Administration for Adolescent Depression

This study is testing whether a probiotic supplement — a product containing beneficial live bacteria — can help reduce symptoms of depression in young people aged 15 to 24 who are already taking an SSRI antidepressant but still experiencing significant depressive symptoms. Research suggests the gut-brain connection may play a role in mental health, and probiotics might enhance the effect of antidepressants. All study visits are conducted remotely via video call. **You may be eligible if...** - You are between 15 and 24 years old - You have been diagnosed with a depressive disorder (such as major depressive disorder or persistent depressive disorder) - You have been taking an SSRI antidepressant for at least 8 weeks - You still have significant depressive symptoms (BDI-II score above 13) - You are fluent in English and have access to a device with video calling capability - You are under the care of a doctor or mental health professional **You may NOT be eligible if...** - Your primary diagnosis is something other than a depressive disorder (e.g., schizophrenia, bipolar disorder) - You are currently not on an SSRI or have been on one for less than 8 weeks - You have unstable or unmanaged ADHD treated with stimulant medications - You do not have reliable internet access or a device for remote visits Talk to your doctor to see if this trial is right for you.