This study explores how well a medicine called brenipatide works for adults with bipolar disorder, a mental health condition causing mood swings. The study also checks for any side effects. Participants will receive either brenipatide or a placebo (a fake medicine) along with their usual treatment. The study lasts up to 9 months, including a 1-month screening period to see if participants meet the study criteria, at least 6 months of treatment, and a 2-month follow-up.

To join, participants need to have a diagnosis of bipolar disorder and be on stable medication. They must attend study visits and follow instructions, like injecting the study treatment themselves and keeping diaries. Those with certain other mental health disorders, severe substance or alcohol use problems, or who are at risk of suicide cannot participate.

• The study lasts up to 9 months with regular visits.
• Participants will self-inject the study treatment.
• People at risk of suicide or with other severe mental health issues can't join.