Xenon Inhalation Therapy for Major Depressive Disorder and Bipolar Disorder

This trial is studying whether breathing a small amount of xenon gas (an inert gas with possible mood-stabilizing properties) can help relieve depression in people with major depressive disorder (MDD) or bipolar disorder. **You may be eligible if...** - You have been diagnosed with major depressive disorder or bipolar depression (per standard diagnostic criteria) - You are aged 18–65 years - Your depression score on a standardized scale is 20 or above (indicating moderate-to-severe depression) - You have been on a stable antidepressant or mood stabilizer for at least 4 weeks - You have reliable transportation to and from the clinic after treatments **You may NOT be eligible if...** - You are not currently on medication for your depression or bipolar disorder - You have a history of psychosis or active suicidal intent - You have severe lung or breathing problems - You are pregnant or breastfeeding - You have had recent changes in your psychiatric medications Talk to your doctor to see if this trial is right for you.