ObjectiveTo evaluate the effects of ketamine treatment on depression and suicidal ideation in treatment resistant depression (TRD) and to determine whether they are influenced by other psychiatric and personality comorbidities. MethodsA randomized double-blind parallel-arm controlled study on 36 patients with TRD. Patients were divided into two treatment groups: ketamine (K group) and placebo (P group). Patients in the K and P groups received one infusion of medicine per week for two weeks. All participants were assessed using the Structured Interview for the Five-Factor Personality Model (SIFFM), Hamilton Depression Rating Scale (HDRS), Suicide Probability Scale (SPS), and Symptom Checklist 90 (SCL 90). ResultsAfter treatment, there was a significant decrease in the total HDRS and SPS scores in the K group compared to the P group, but the magnitude of response was not influenced by the presence of other psychiatric symptoms. Regression model, only receive ketamine treatment was significant factor for improve suicide and depression scores. Limitationslack of data on other outcomes that are important to patients (e.g., quality of life, cognition) and need for a larger sample size. ConclusionsKetamine infusions in TRD reduce suicidal ideation and depression despite the presence other psychiatric and personality disorders.