Drug treatment for IBS is usually directed at the most predominant symptom so, for example, patients with mainly constipation may be treated with laxatives and patients with cramping pain with antispasmodics.

The research into IBS provides limited evidence as drug trials are usually short (rarely more than 12 weeks) and there is often a strong placebo response, so differences between active treatment and placebo may be small. It is important to explain to the patient that they may need to try various therapies until they find those that suit them the most.

Laxatives

Traditionally, patients with IBS were advised to eat a diet high in fibre and raw wheat bran was often recommended as a way of increasing the fibre intake. However, bran, which is an insoluble fibre, is no longer recommended in IBS as it has been shown to aggravate symptoms.

Oats and oat bran are more soluble than wheat bran and are better tolerated. Bulk-forming laxatives (containing soluble fibre) such as ispaghula husk or sterculia act by retaining fluid within the stool and increasing faecal mass, stimulating peristalsis and they also have stool-softening properties.

It may take a few weeks of experimentation to find the dose that suits an individual patient. Remind the patient to increase fluid intake to take account of the additional fibre.

Osmotic and stimulant laxatives are sometimes used but may aggravate the condition and evidence in IBS is poor. Ideally their use should only be under medical supervision. Lactulose is generally avoided as it can cause bloating.