Pharmacology Approaches for IBS

The prescription of medications in conjunction with the dietary management of IBS has been quite successful in the literature.

As a dietitian my first point of call will always be diet first, though for some this may not be enough and the need for medications may be necessary. Therefore, I thought I would discuss some of the common medications used in the treatment of IBS.


Firstly, you should always consult your health care practitioner before commencing any medication. When discussing the commencement of a new medication with your practitioner it is always important to inform them:

  • of any other medications including herbal preparations you may be taking
  • whether you are pregnant, planning to become pregnant, or are breast-feeding
  • if you have allergies to medicines, foods, or other substances
  • if you have AIDS or liver problems
  • if you are taking an antibiotic

This is by no means an extensive list of what may affect a new medication and every medication is different hence the importance of consulting a health care professional before the commencement of a new medication, herbal preparation or dietary supplement [1].

IBS-C – Laxatives

IBS-C patients tend toward constipation which is consistent with the passing of hard, dry bowel motions that may be infrequent or difficult to pass. Typically, most cases of constipation are treated successfully by eating a high fibre diet, drinking plenty of fluids and daily exercise [2]. Over- the counter laxatives are fine to take in the short term, however if the problems consists you will need to seek advice from a health care professional. It is important to note that chronic constipation is not without risks, complications can include: haemorrhoids, faecal impaction and rectal prolapse [2].

Common laxatives prescribed to patients suffering IBS-C

Lactulose helps alleviate constipation by drawing water into the colon to soften stools. However, in some cases can exacerbate symptoms. If symptoms are exacerbated the patient should discuss modifying their dose with their practitioner or discuss the use of a different laxative [1].

Linaclotide works by increasing the amount of fluid in the intestines and causing the contents to move along more quickly. Generally it is not to be used in children under the age of 18 [1].

IBS-D – Common Antimotility Medication

IBS-D patients tend toward diarrhoea.  A sudden onset of diarrhoea lasting less than 14 days, though usually resolving after a day or two, is known as acute diarrhoea. The most common cause of acute diarrhoea is food poisoning or gastroenteritis causing the intestinal lining to become irritated and inflamed, consequently hindering the absorption of water from food waste [3]. Chronic diarrhoea, however, lasts for four weeks or more and can be caused by a range of conditions including irritable bowel syndrome (IBS) [3].


Loperamide is an antidiarrheal agent, which works by slowing the movement of bowel contents and is usually the first antimotility agent used for patients with IBS-D. There are no common side effect with this product, however if you do experience severe side effects contact your health professional immediately [1].

Tricyclic Antidepressants

For some, laxatives, loperamide and antispasmotic agents are ineffective. For these patients there is some evidence for tricyclic antidepressants (TCAs) [4]. Patients with IBS have increased visceral hypersensitivity and dysregulation of central pain perception in the gut-brain axis (essentially they feel more pain when the colon expands due to increased gas production) [5]. Antidepressant agents can help to partially increase this central pain threshold but can also express their effect via regulation of gastrointestinal transit [5].

Typically, TCAs with the least anticholinergic effects (drugs which inhibit the transmission of parasympathetic nerve impulses, thereby reducing spasms of smooth muscles i.e. doxepin and desipramine) are used for patients with IBS-C and imipramine or amitriptyline for IBS-D patients. Numerous side effects are possible with TCA’s including: dry mouth, blurred vision, sweating, dizziness, drowsiness, restlessness, racing heart beat etc. If serious side effects are experienced you should contact your health professional immediately.

If TCA’s are ineffective the next step is usually the prescription a different type of antidepressants known as selective serotonin reuptake inhibitors. Again, with these drugs it is imperative that patients are monitored carefully due to the potential side-effects [4].


To conclude, dietary changes should always be the first point of call before medications are considered for IBS. Many medications have proven beneficial effects in reducing uncomfortable symptoms caused by IBS, though many drugs are not without potential side effects. Always consult your health care professional before taking a new medication and seek immediate assistance if you experience severe side effects. Diet should always be a key factor in the treatment of IBS and should be used in conjunction with medication, when medications are necessary.



  4. NICE Guidelines, irritable bowel syndrome in adults: diagnosis management.
  5. Rahimi R, Nikfar S, Rezaie A, Abdollahi M. Efficacy of tricyclic antidepressants in irritable bowel syndrome: A meta-analysis. World J Gastroenterol. 2009 Apr 7; 15(13): 1548–1553.
Pharmacology Approaches for IBS
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