Lithium Versus Cariprazine in the Acute Phase Treatment of Bipolar Depression (DUAG9)

Inclusion Criteria: * A diagnosis of bipolar disorder, type 1 or type 2, and a current episode of depression according to DSM-5 * Severity of depression: A score of at least 21 on the self-reported Major Depression Inventory (MDI). * No start or dose increase of psychotropic medication (except for benzodiazepines and benzodiazepine-like drugs (zopiclone, zolpidem, and melatonin)) in the two weeks prior to inclusion. * No new start of formalized psychotherapy sessions, excluding psychoeducation, during the 4 weeks prior to inclusion. * Age criteria: Subjects must be at least 18 years old and below 65 at the time of randomization. * The duration of the current depressive episode must be between 4 and 52 weeks as judged by the investigator at the time of randomization. * Clinical uncertainty regarding which of the alternatives, cariprazine and lithium, would be the better choice in the specific case. * Female participants should be sterile or non-fertile or, in case of being fertile, they must have a negative pregnancy test AND use safe anticonception. * Signed document of informed consent. Exclusion Criteria: * Prior or ongoing acute treatment of a depressive episode lasting \> 14 days with either lithium or cariprazine as judged by the investigator. * ECT within the current depressive episode. * A score of MAS \> 6. * A diagnosis of dementia. * High risk of non-adherence at the investigator's discretion. * Not understanding the Danish language as judged by the investigator * Psychiatric coercion in the form of forced admission or detainment OR sentence to forensic psychiatric care. * Presence of clinically relevant delusions, hallucinations or other psychotic symptoms as judged by the investigator. * Suicidality according to C-SSRS with a positive response to question 4 or 5 or upon investigator's discretion. * Medical conditions like cancer, kidney failure, epilepsy, deep brain stimulation device, or other medical conditions interfering with study the outcome and safety as judged by investigator's discretion. * Current harmful use or dependency of alcohol or drugs according to DSM-5. * Known allergy to any of the substances in the study medication.