This study is for people with Major Depressive Disorder (MDD) who feel little joy or pleasure, known as anhedonia. We're looking at patients who aren’t feeling better with their current antidepressant, specifically those using Selective Serotonin Reuptake Inhibitors (SSRI) or Serotonin Norepinephrine Reuptake Inhibitors (SNRI). These medicines help with depression by affecting brain chemicals. To join, you need to be starting a new treatment to help your depression or switching to a single new medication in the US. You must have had some relief from your current treatment but not enough. If you have other mental health issues like psychosis or bipolar disorder, or serious health problems, you cannot join. You must be able to understand and agree to the study. The study will follow how you and others respond to these treatments.

• The study observes your treatment for MDD and changes you make.
• Participation requires starting a new or add-on antidepressant treatment.
• The study will help understand how these treatments work for people with MDD.