Inclusion Criteria:

* Has a ≥4 week history of AjD as defined by DSM-5-TR with either depressed mood, or mixed anxiety and depressed mood confirmed by clinical interview with evidence that the AjD was instigated by one of the following medical illnesses (e.g., diagnosis, impact, management, recurrence, prognosis): Cancer, ALS, MS, PD or IPF
* Is sufficiently ambulatory and capable of self care as necessary to complete study procedures
* Has normal cognitive function
* Is on stable use of antidepressants or psychotherapy, or is willing to delay use until the end of study
* If female is not pregnant or planning to become pregnant. If male is not planning to make a partner pregnant
* Is willing and able to comply with the conditions and requirements of the study

Exclusion Criteria:

* Has a significant risk of suicide
* Has active or medical history of bipolar disorder, schizophrenia, schizoaffective disorder, psychotic disorder and/or borderline personality disorder, or first-degree family history of psychosis or bipolar disorder
* Has active or a history of central nervous system malignancy
* Has other medically significant conditions rendering unsuitability for the study
* Has used or will need to use prohibited medications or therapies
* Has a known sensitivity or intolerance to study intervention or potential rescue medications