A number of drugs may be prescribed and it is worth understanding how these are being used, particularly if the patient is considering purchasing other treatments.

Linaclotide is specifically indicated for moderate to severe IBS with constipation. It acts as a laxative and works by stimulating enzymes in the gut to increase intestinal secretion. NICE advises that patients who have not responded to laxatives and who have had constipation for at least 12 months can be treated with linaclotide. The main side-effects are abdominal distension, abdominal pain, diarrhoea, dizziness and flatulence.

Amitriptyline at low dose (usually 10-30mg at night), an unlicensed indication, can be used for abdominal pain or discomfort as a second-line option in patients who have not responded to antispasmodics, antimotility drugs or laxatives. A relative contraindication to amitriptyline is chronic constipation, which may limit its use in some patients. Concomitant treatment with hyoscine is best avoided because of enhanced antimuscarinic/anticholinergic activity.

A selective serotonin reuptake inhibitor (SSRI) such as citalopram or fluoxetine may be considered in those who do not respond to a tricyclic antidepressant (again, an unlicensed use).