This clinical trial is focused on studying Major Depressive Disorder (MDD), a condition characterized by persistent feelings of sadness and loss of interest. The study specifically targets individuals with moderate-to-severe anhedonia, which is a reduced ability to feel pleasure. The treatment being tested is a medication called Aticaprant, which is taken in tablet form. It is used alongside an antidepressant, which is a type of medication that helps to relieve symptoms of depression. The purpose of the study is to evaluate how effective Aticaprant is in preventing the return of depressive symptoms in people who have already shown improvement with their current treatment.

Participants in the study will be randomly assigned to receive either Aticaprant or a placebo, which looks like the medication but does not contain the active substance. The study is designed to be double-blind, meaning neither the participants nor the researchers will know who is receiving the actual medication or the placebo. This helps to ensure that the results are not influenced by expectations about the treatment. The study will take place over a period of time, during which participants will continue their usual antidepressant treatment while also taking the study medication or placebo.

The main goal is to see how long it takes for depressive symptoms to return, if they do, after starting the study treatment. This information will help researchers understand if Aticaprant can effectively delay the relapse of depression symptoms in people with MDD and anhedonia. Participants will be monitored regularly to assess their response to the treatment and to ensure their safety throughout the study.