Irritable Bowel Syndrome (IBS)
Diagnosis, dietary management and pharmacological treatment per NICE CG61
Irritable bowel syndrome is a functional bowel disorder characterised by abdominal pain or discomfort associated with altered bowel habit, in the absence of any identifiable organic pathology. It is one of the most common conditions seen in primary care and gastroenterology clinics, affecting up to 10–20% of the population. Diagnosis is clinical, based on the Rome IV criteria, and management combines dietary modification, antispasmodics, and psychological support.
What is IBS?
IBS is a chronic, relapsing functional gastrointestinal disorder. It is defined by the Rome IV criteria as recurrent abdominal pain at least one day per week for three months, associated with two or more of the following: related to defecation, a change in stool frequency, or a change in stool form. Symptom onset must be at least six months before diagnosis. IBS is subtyped as IBS-D (diarrhoea-predominant), IBS-C (constipation-predominant), IBS-M (mixed), or IBS-U (unclassified). There is no structural or biochemical abnormality — it is a disorder of gut-brain interaction.
Diagnosis and Red Flags
NICE CG61 recommends a clinical diagnosis without routine blood tests unless red flags are present. If there is diagnostic uncertainty, FBC, ESR or CRP, coeliac serology (tTG-IgA), and faecal calprotectin should be checked. Calprotectin is normal in IBS but raised in inflammatory bowel disease. Red flags requiring urgent investigation include rectal bleeding, unintentional weight loss, onset after age 50, family history of bowel or ovarian cancer, nocturnal symptoms, and iron-deficiency anaemia.
Pharmacological and Dietary Management
First-line treatment for pain and bloating includes antispasmodics — mebeverine, hyoscine butylbromide, or peppermint oil capsules. For IBS-C, ispaghula husk or macrogol are preferred; lactulose should be avoided as it worsens bloating. For IBS-D, loperamide is used. Second-line options for refractory pain include low-dose amitriptyline or an SSRI. Linaclotide is reserved for severe IBS-C when other treatments have failed. A dietitian-led low FODMAP diet is recommended, alongside regular meals, reduced caffeine, and stress management. CBT is recommended by NICE if symptoms persist beyond 12 months.