The purpose of this clinical trial is to learn if Bifidobacterium has antidepressant-like effects by enhancing creatine absorption in adults. The main questions to be answered are

Does Bifidobacterium combined with creatine have better antidepressant effects? Does Bifidobacterium enhance exogenous creatine uptake?

Researchers will compare bifidobacterium combined with creatine with placebo to see if bifidobacterium combined with creatine has antidepressant effects.

Participants will:

Take bifidobacterium, creatine or placebo every day for 4 weeks. Keep a diary of their symptoms and collect blood samples.

Inclusion Criteria for depression:

• Adults age 18-60 years inclusive.
• Current diagnosis of major depression disorder (MDD) identified by the Structured Clinical Interview for Diagnostic and Statistical Manual of Mental Disorders-5 (SCID-5).
• Current Hamilton Depression Scale 17 score of > 16.
• BMI (body Mass Index) between 18 and 28 kg/m²
• Right-handed

Exclusion Criteria:

• Diagnosis of bipolar disorder, schizophrenia, or schizoaffective disorder, identified by the SCID-5.
• History of or current diagnosis of acute kidney injury (AKI), chronic kidney disease (CKD) or end-stage renal disease (ESRD)
• History of seizure disorder
• Current serious suicide risk identified by the Columbia Severity Suicide Rating Scale
• Previous diagnosis of creatine deficiency syndrome or evidence of creatine deficiency syndrome
• Antibiotic use in last 30 days
• Probiotics use in last 30 days
• Positive pregnancy test
• Breastfeeding