Five eligible studies reporting on 47 depressed patients (range, 1-18 patients) were identified. Two studies were conducted among adults with treatment-resistant depression, 1 study among depressed inpatients, and 2 studies among patients from special populations (geriatric nursing home, human immunodeficiency virus-associated encephalopathy). All studies evaluated the effects of pharmacologic treatments (methylphenidate, D-amphetamine, ketamine, and sulpiride). Three studies compared an off-label treatment with placebo, 1 study compared 2 off-label treatments, and 1 study compared escalating doses of an off-label treatment with placebo. All 4 studies with more than 1 participant demonstrated heterogeneous treatment effects. All studies produced data that could personalize treatment selection for individual patients. No studies reported on recruitment challenges, compliance with self-tracking, or satisfaction with participation.