1. Introduction “The good physician treats the disease; the great physician treats the patient who has the disease.” — Sir William Osler Advances in modern medicine have substantially improved survival from many acute and chronic illnesses; however, psychiatric disorders remain common among medically ill patients and significantly influence their clinical outcomes. Approximately 30–50% of hospitalised medical patients have a diagnosable psychiatric disorder, with delirium, depression, anxiety disorders, adjustment disorders, and substance use disorders being the most frequently encountered conditions. Despite their high prevalence, these disorders are often under-recognised and undertreated, resulting in prolonged hospitalisation, poor treatment adherence, increased healthcare costs, greater morbidity, and higher mortality. Consequently, integration of psychiatric care into routine medical practice has become an essential component of comprehensive patient-centred care (1, 2). Definition of a Medically Ill Patient A medically ill patient is an individual with an acute or chronic physical illness requiring medical or surgical treatment. Psychiatric disorders occurring in these patients may represent: • pre-existing psychiatric illnesses, • manifestations of an underlying medical disorder, • adverse effects of medications or medical treatments, or • psychological reactions to illness and hospitalization. The relationship between physical illness and mental health is bidirectional, with each influencing the onset, course, treatment response, and outcome of the other. Therefore, early recognition and appropriate psychiatric intervention are essential for improving both psychiatric and medical prognosis.(1,2) Consultation-Liaison Psychiatry Consultation-Liaison (C-L) Psychiatry (formerly termed Psychosomatic Medicine) is the subspecialty of psychiatry concerned with the assessment, diagnosis, treatment, and prevention of psychiatric disorders occurring in patients receiving medical or surgical care The term comprises two complementary functions: • Consultation – Psychiatric evaluation and treatment provided at the request of another medical or surgical specialty. • Liaison – Ongoing collaboration with physicians, surgeons, nurses, psychologists, social workers, rehabilitation professionals, and other members of the multidisciplinary team to integrate psychiatric principles into comprehensive patient care. Thus, modern Consultation-Liaison Psychiatry extends beyond bedside consultation to include collaborative care, education of healthcare professionals, prevention of psychiatric complications, ethical consultation, assessment of decision-making capacity, and development of integrated care pathways based on the biopsychosocial model. (3) "Consultation-Liaison Psychiatry has often been described as the bridge between psychiatry and the rest of medicine." ________________________________________ Brief Historical Perspective Consultation-Liaison Psychiatry evolved during the early twentieth century with the growth of general hospitals and the psychosomatic medicine movement. The development of George Engel's biopsychosocial model and the pioneering work of Lipowski established the speciality as the interface between psychiatry and medicine. Today, Consultation-Liaison Psychiatry is an established subspecialty providing comprehensive psychiatric care through multidisciplinary collaboration (3–5) Scope of Consultation-Liaison Psychiatry The scope of Consultation-Liaison Psychiatry extends far beyond diagnosis and treatment of psychiatric disorders. It includes prevention of psychiatric complications, behavioural management, capacity assessment, ethical consultation, psychoeducation, collaborative care, and integration of psychiatric principles into general medical practice. C-L psychiatrists are increasingly involved in intensive care units, oncology, transplant medicine, palliative care, rehabilitation, and emergency medicine, reflecting the growing recognition that optimal healthcare requires simultaneous attention to both physical and mental health. (1,5,6) Typical Reasons for Psychiatric Consultation in Medically Ill In-patients Common indications for psychiatric consultation (adapted from Lipowski) include: (4,5) 1. Suicide attempt or suicidal ideation 2. Delirium or unexplained behavioural disturbance 3. Depression, anxiety, or excessive emotional reactions to illness 4. Refusal of investigations or treatment 5. Psychiatric adverse effects of medications 6. Alcohol or substance withdrawal 7. Assessment of decision-making capacity 8. Pre-operative or pre-transplant psychiatric evaluation 9. Delayed recovery or prolonged hospitalization without obvious medical explanation 10. Discharge planning and psychosocial rehabilitation Clinical Spectrum of Problems Encountered in Consultation-Liaison Psychiatry Table 1.1. Clinical Spectrum of Problems in Consultation-Liaison Psychiatry (Adapted from Kaplan & Sadock's Comprehensive Textbook of Psychiatry) Importance of Psychiatric Assessment Psychiatric assessment in medically ill patients extends beyond establishing a psychiatric diagnosis. It differentiates primary psychiatric disorders from psychiatric manifestations of medical illness, identifies medication-induced syndromes, and evaluates cognition, decision-making capacity, suicide risk, and psychosocial factors. Thus, comprehensive psychiatric assessment forms the cornerstone of effective Consultation-Liaison Psychiatry and provides the foundation for evidence-based management of medically ill in-patients. (1,2)