This study is for people with Major Depressive Disorder (MDD), a condition causing long-term feelings of sadness. The study looks at how safe and tolerable a treatment called NBI-1065845 is when added to other depression medicines. To join, participants must have MDD or a similar condition and have tried antidepressants for at least 8 weeks without much success. They should be willing to follow all study rules. However, if someone has had another significant mental health issue in the past year or is at risk of harming themselves or others, they cannot join.

• Duration: This is a long-term study, so it may last several months.
• Visits: Participants will need to visit the study site regularly.
• Safety: The main goal is to see if the treatment is safe over time.

Participants will be helping researchers understand how well the treatment works alongside their current medication and its safety for long-term use.