Objective: The aim of this Randomized Controlled Trial (RCT) is to present the initial findings of a larger RCT study conducted internationally for the first time, regarding the hypothesis, when the Integrated Psychological Therapy (IPT) for individuals with schizophrenia is more and when it is less effective, regarding Treatment-Resistant Schizophrenia (TRS) and nontreatment resistant schizophrenia (NTRS). Methods: Forty-eight outpatients with schizophrenia of an adult psychiatric department participated in this RCT study. Eleven outpatients of IPT and 11 of the Treatment as Usual (TAU) belong to TRS. Thirteen patients of IPT and 13 of TAU belong to NTRS. A test battery was given at baseline after therapy (10 weeks) and at 3 months' follow-up. Neurocognition, social cognition, psychopathology, and functional outcome were assessed. The General Linear Model (GLM) for repeated measurements was used. Effect sizes, z-scores, and the sign test were calculated. Results: There was a statistical significance for verbal memory; positive, negative symptoms and general psychopathology; Global Assessment and Functioning scale (GAF) and quality of life favoring NTRS. Effect sizes showed superiority of NTRS in comparison to TRS. The sign test showed a significant improvement in Integrated Psychological Therapy treatment-resistant schizophrenia (IPTTRS) that was maintained in the follow-up, in Integrated Psychological Therapy nontreatment resistant schizophrenia (IPTNTRS) and in Treatment as Usual nontreatment resistant schizophrenia (TAUNTRS). Conclusion: The IPT is more effective in NTRS in comparison to TRS, although IPTTRS showed some improvements, maintained at follow-up. Further RCT studies with larger samples are needed.