A Study of Elpipodect (MK-8189) in Participants With Bipolar I Disorder (MK-8189-020)

Prior treatment

• History of seizure disorder beyond childhood or is receiving treatment with any anticonvulsant to prevent seizures.
• Major surgery or donation/loss of 1 unit of blood within 4 weeks prior to screening.
• Received any vaccine starting from 30 days prior to study intervention or is scheduled to receive any vaccine through 30 days following study intervention.

Other illness

• Untreated or uncompensated endocrine, gastrointestinal, cardiovascular, hematological, hepatic, immunological, renal, respiratory, genitourinary, or major neurological abnormalities or diseases.
• Evidence or history of a primary DSM-5 axis I psychiatric diagnosis other than those specified for inclusion.
• History of cancer (malignancy).
• Evidence or history of mental retardation, borderline personality disorder, or organic brain syndrome.
• History of neuroleptic malignant syndrome or moderate to severe tardive dyskinesia.
• Substance-induced psychotic disorder or behavioral disturbance.
• DSM-5 TR defined substance use disorder within 3 months of screening.
• Positive test(s) for hepatitis B surface antigen, hepatitis C antibodies or human immunodeficiency virus.

Other

• The main exclusion criteria include but are not limited to the following:

• The main inclusion criteria include but are not limited to the following:
• Meets diagnostic criteria for bipolar I disorder, manic or mixed features according to the Diagnostic and statistical manual of Mental Disorders TR (DSM-5 TR) and considered to be in a non-acute phase of their illness.
• History of receiving and tolerating antipsychotic medication within the usual dose range employed for bipolar I disorder.
• Body mass index is 18 and 40 kg/m\^2, inclusive.
• If currently taking an antipsychotic, is able to discontinue use at least 5 days prior to study start and the duration of the study.