Clinical global impression
The Clinical Global Impression (CGI) scale is a standardized, clinician-rated instrument that provides a broad assessment of a patient's overall severity of psychiatric illness and degree of improvement following treatment, drawing on the clinician's global judgment informed by all available information about the patient.[1] Originally developed in 1976 by William Guy for the National Institute of Mental Health's Early Clinical Drug Evaluation Unit (ECDEU) as part of a manual for psychopharmacology assessments, the CGI has become a cornerstone tool in psychiatric research and practice due to its applicability across all major mental disorders, including schizophrenia, depression, and bipolar disorder.[2][1] The scale originally comprised three subscales: the CGI-Severity of Illness (CGI-S), which rates current symptom severity on a 7-point scale from 1 (normal, not at all ill) to 7 (among the most extremely ill); the CGI-Global Improvement (CGI-I), which evaluates change from baseline on a 7-point scale from 1 (very much improved since starting treatment) to 7 (very much worse since starting treatment); and the CGI-Efficacy Index, a 4x4 matrix that weighs treatment efficacy against side effect severity. However, the Efficacy Index has not been used in recent trials and is not included in the current version of the CGI, with contemporary applications focusing primarily on the CGI-S and CGI-I.[3][1] Its design emphasizes clinical expertise over rigid criteria, allowing for quick administration—typically under one minute by trained raters—and has demonstrated reliability in correlating with comprehensive symptom inventories like the Hamilton Depression Rating Scale or Brief Psychiatric Rating Scale.[1] Over the past nearly five decades, the CGI has been integral to thousands of clinical trials, including those supporting FDA approvals for psychotropic medications, while also aiding routine clinical monitoring to guide adjustments in therapy and document outcomes for regulatory or reimbursement purposes.[1][2]Introduction
Definition and Purpose
The Clinical Global Impression (CGI) is a standardized, three-item, clinician-rated assessment tool developed to evaluate the overall clinical progress of patients with psychiatric disorders, emphasizing the clinician's holistic judgment of the patient's global status rather than itemized symptom counts.[1] Originating in the 1970s within National Institute of Mental Health-sponsored psychopharmacology research, it serves as a simple, standalone measure applicable across diverse diagnoses.[4] The primary purposes of the CGI include establishing baseline severity of illness, monitoring changes in patient condition over time, and gauging treatment efficacy through a non-specific, global lens that captures therapeutic benefits and side effects without requiring disorder-specific criteria.[3] This approach enables its use in both routine clinical practice and clinical trials, where detailed symptom scales may be impractical.[1] Structurally, each of the CGI's three components employs a 7-point ordinal scale, allowing for rapid completion—typically under 5 minutes—while drawing on the rater's clinical expertise and familiarity with the patient's history.[5] Its brevity and reliance on professional judgment make it particularly valuable for capturing nuanced, real-world impressions of patient functioning in time-constrained environments.[6]Historical Development
The Clinical Global Impressions (CGI) scale originated in the 1970s as a standardized tool for assessing treatment outcomes in psychiatric research, amid the rapid expansion of psychopharmacological investigations following the introduction of new antipsychotic and antidepressant medications. It was formally introduced in the 1976 revised edition of the ECDEU Assessment Manual for Psychopharmacology, compiled by William Guy under the auspices of the National Institute of Mental Health (NIMH)'s Early Clinical Drug Evaluation Unit (ECDEU) program, which had been active since 1959. This manual integrated the CGI into a broader battery of instruments designed for NIMH-sponsored clinical trials, aiming to provide a brief, clinician-based global evaluation of patient severity, improvement, and therapeutic efficacy across diverse psychiatric populations, including those with schizophrenia and anxiety disorders.[1] The initial purpose of the CGI was to address inconsistencies in outcome measurement during an era of burgeoning drug development, offering a simple 7-point rating system that relied on the clinician's overall experience rather than symptom-specific checklists, thereby facilitating cross-study comparisons in psychopharmacological trials. By the 1990s, the scale's versatility led to its adoption beyond psychiatry, particularly in Alzheimer's disease clinical trials, where structured variants like the Clinician's Interview-Based Impression of Change (CIBIC) and the Alzheimer's Disease Cooperative Study-Clinical Global Impression of Change (ADCS-CGIC) were developed to enhance reliability in assessing cognitive and functional changes. A key evolution occurred in 2007, when Busner and Targum proposed guidelines for its improved application in clinical practice—the so-called improved CGI (iCGI)—to mitigate limitations such as rater bias influenced by irrelevant adverse events or unstructured narratives, emphasizing standardized anchors and comprehensive patient history integration.[1][7] The CGI's milestones include its widespread integration into regulatory processes, notably contributing to U.S. Food and Drug Administration (FDA) approvals for antipsychotics like olanzapine and antidepressants such as the olanzapine-fluoxetine combination for treatment-resistant depression, where it served as a primary endpoint for demonstrating clinical efficacy in pivotal trials. In the 2020s, updates have focused on hybrid versions that incorporate patient perspectives, such as the Patient Global Impression of Change (PGIC) scales paired with traditional CGI ratings, aligning with FDA guidance on patient-reported outcomes to better capture subjective treatment responses in diverse therapeutic contexts, including adaptations for autism spectrum disorder clinical trials and a severity scale for primary biliary cholangitis as of 2025.[8][9][10][11]Components of the CGI
CGI-Severity Scale
The CGI-Severity (CGI-S) scale is a clinician-rated measure that evaluates the overall severity of a patient's illness at a specific point in time, serving as the baseline component of the Clinical Global Impressions framework.[1] It relies on the rater's total clinical experience with patients who have the same diagnosis, incorporating all available information such as patient interviews, behavioral observations, historical records, and collateral reports from family or charts, without focusing on etiology or specific symptoms.[1] This approach emphasizes a holistic impression of the patient's current status relative to typical individuals with the same condition, typically assessed over the past seven days unless otherwise specified.[1] The scale employs a 7-point ordinal rating system, where clinicians select the single score that best captures the patient's severity:- 1: Normal, not at all ill
- 2: Borderline mentally ill
- 3: Mildly ill
- 4: Moderately ill
- 5: Markedly ill
- 6: Severely ill
- 7: Among the most extremely ill patients[1]