This study is investigating if blocking a specific inflammation signal in the body, called **Janus kinase (JAK) signaling**, can help people with depression, especially those with high inflammation. **Baricitinib** is a medicine used to block this signal and will be compared to a placebo, which is a fake pill that looks the same. Researchers will look at how this affects the brain, motivation, and movement in people with major depression and high inflammation.

• The study lasts 8 weeks and includes at least 8 visits over 2-3 months.
• Participants must stop antidepressants 4-8 weeks before starting the study.
• Participants will undergo blood tests, brain scans, and receive compensation for their time.

Participants must be between 25-55 years old, diagnosed with major depression or bipolar disorder, and have high inflammation markers. They cannot have serious medical conditions, infections, or be taking certain medications. Consent will be obtained, and blood and test results will be saved for future research.