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Laxatives and Antidiarrhoeals


Constipation and Diarrhoea

Bowel Movement Habit

Bowel movement (the time pattern of discharging stool) varies a lot between individuals.


Constipation is hard to define but usually has following features:
  • infrequent bowel movements
  • have to strain yourself when discharging stool
  • stools are hard and lumpy
  • blocking feeling around the anus
  • pain when discharging stool
Constipation can lead to abdominal discomfort, appetite loss, piles (haemorrhoid), bleeding stools and even low back pain.

The reason for constipation includes poor eating habit (e.g. inadequate fibrous food and water intake), poor exercise habit, and habitually delaying the urge to toilet. Besides, constipation can also be caused by emotions, medications, and underlying medical condition.


If you have loose and watery stools, it may be diarrhoea.

For diarrhoea, apart from stomach cramp, you may have nausea and vomiting. Your anus area may also become red. Because you are losing excessive water from the stools, you may feel very weak. Sometimes, diarrhoea is accompanied by headache and fever.

Diarrhoea is usually caused by poor eating hygiene (e.g. raw and contaminated food) and drinking from uncleaned water source. Poor personal hygiene may exacerbate the problem of diarrhoea. Apart from these, medications, emotions, and other underlying medical condition can also lead to diarrhoea.


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Treatment used


(I) For constipation

In most cases of constipation, simple changes in the lifestyle and modify the diet with high fibre and increase fluid intake can help relieving the symptoms of constipation. In the case where the constipation is caused by side effect of drug or underlying medical condition, consult a healthcare provider to assess if there is a need to switch to another medication that is not likely to cause constipation, or consider treating the underlying disease first. However, when these are not effective or unfeasible, laxatives may be used with medical consultation.

(II) For diarrhoea

Most cases of diarrhoea are self-limiting, which means that diarrhoea can be recovered after a few days without treatment. In severe or persistent diarrhoea, drinking plenty of fluids and replenishing electrolyte to avoid dehydration is of primary importance. Antidiarrhoeal is rarely necessary, but a short course as advised by healthcare professionals may be considered useful to reduce the symptomatic discomfort and inconvenience of frequent bowel movements.


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Form of products

Most of the laxatives and antidiarrhoeals are over-the-counter medicines and are taken orally in forms of liquids, tablets, capsules, powders etc. For constipation of stuffy hard stool, rectal preparations such as suppositories or enemas may be considered.


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Classification of Laxatives

In general, laxatives can be classified into four main categories: bulk laxatives, stimulant laxatives, osmotic laxatives and stool softeners.

Bulk laxatives relieve constipation by forming soft and bulky stool; and by promoting contraction of intestinal muscles. They are generally considered the safest and are appropriate for patients with small hard stools. Nevertheless, they do not work until after a few days of consumption and patients need to take plenty of fluids. Examples of bulk laxatives include methylcellulose, wheat bran, ispaghula, psyllium and sterculia.

Stimulant laxatives speed up the bowel movement by stimulating the contraction of intestinal muscles. Examples of stimulant laxatives are bisacodyl, senna, glycerol and sodium picosulfate. They have a more rapid onset of action (about 6 to 12 hours) than bulk laxatives, and are usually given at night to help produce a bowel movement the following morning. Glycerol suppositories are normally used when a bowel movement is needed quickly, with onset of action of about 15 to 30 minutes.

Osmotic laxatives draw fluid into the bowel, and facilitate bowel movement with bulky and softer stools. Examples include macrogols, saline laxatives such as magnesium hydroxide, and poorly absorbed sugars such as lactulose or sorbitol.

Stool softeners add moisture to stools, and make them softer and easier to pass out of the body. They have added value for patients with haemorrhoids or anal fissures, or for those who is vulnerable in stool straining, is potentially hazardous such as the elderly or those with existing cardiovascular disease. Docusate is one of the examples.


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Common side effects and precautions of Laxatives

Types of Laxatives
Common side effects
1. Bulk laxatives
  • Bloating and flatulence
  • Abdominal distension
  • Gastro-intestinal obstruction or impaction
  • Hypersensitivity
  • Must be taken with plenty of water, otherwise increase risk of obstruction
  • Should not be taken immediately before going to bed
  • Use with cautions in elderly, or debilitated patients, or those with intestinal narrowing or decreased motility
  • Avoid use in patients with difficulty in swallowing, intestinal obstruction and faecal impaction
2. Stimulant laxatives
  • Abdominal cramp
  • Nausea and vomiting
  • Diarrhoea
  • Local irritation if suppository preparation is used
  • Tolerance
  • Avoid use in patients with intestinal obstruction, acute inflammatory bowel disease and severe dehydration
3. Osmotic laxatives
  • Abdominal pain
  • Bloating and flatulence
  • Nausea and vomiting
  • Avoid use in patients with intestinal obstruction
  • Avoid use of lactulose in patients with galactosaemia
  • Avoid use of saline laxatives in patients with renal and hepatic impairment
  • Avoid use of saline laxatives in patients with heart failure, as saline laxatives contain sodium salt
  • Avoid use of macrogols in patients with severe inflammatory conditions of the intestinal tract such as Crohn’s disease and ulcerative colitis
4. Stool softeners
  • Abdominal cramp
  • Nausea
  • Skin rash
  • Avoid use in patients with intestinal obstruction


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General advice on taking Laxatives

  • Laxatives should only be taken occasionally and on a short-term basis.

  • Overusing laxatives can cause dehydration and unbalanced level of salts and minerals in the body.

  • Long term use of laxatives can lead to dependency and decreased bowel function.

  • Laxatives of multiple-ingredients may not be any more effective than those of single-ingredient, but they may be more likely to cause side effects.

  • Make simple life adaptations to prevent and manage constipation before using any medications, such as eating high-fibre food, drinking plenty of fluid, and doing regular exercise. Remember, do not delay your natural response to discharge your stool.
  • Laxatives have been abused as a slimming aid. Only a balanced diet and regular physical activity are the ways to achieve and maintain an ideal body weight. Please refer to the following link for more information on obesity:

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Classification of Antidiarrhoeals

  • Antidiarrhoeals can be classified into two main categories: adsorbents and antimotility drugs.

  • Adsorbents bind and inactivate bacterial toxins or other substances that cause diarrhoea, however their action is non-specific and may also adsorb nutrients, digestive enzymes or drugs in the gut. Kaolin is one example of adsorbents.

  • Antimotility drugs work by slowing down the bowel movement, which allows more water being absorbed from the stools and results in firmer stools and that the bowel movement becomes less frequent. Examples of these include loperamide and diphenoxylate.

  • But antidiarrhoeal drug should best be avoided in children for diarrhoea. Do not try to give medicines without medical advice. For the adult, please follow the instruction on label of your medication. Do not abuse or overdose.


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Common side effects and precautions of Antidiarrhoeals

Types of Laxatives
Common side effects
1. Adsorbents
  • Constipation
  • Bloating
  • Fullness
  • Not recommended for acute diarrhoea
2. Antimotility drugs
  • Abdominal bloating or cramp
  • Nausea and vomiting
  • Dry mouth
  • Constipation
  • Dizziness
  • Drowsiness
  • Skin rash
  • Should be avoided in patients with abdominal distension, or antibiotic-associated colitis
  • Use with caution in patients with hepatic impairment


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General advice on taking Antidiarrhoeals

  • Antidiarrhoeals should only be taken occasionally and on a short term basis.

  • Antidiarrhoeals are used for the symptomatic relief of diarrhoea and are not curative.

  • Oral rehydration solution, although not an antidiarrhoeal, is often used as first-line for replenishing fluids for diarrhoea patient, especially those with acute diarrhoea; and is suitable for children.

  • Make simple life adaptations to prevent and manage diarrhoea before using any medications, such as taking plenty of rest, avoiding fatty, spicy or heavy food and drinking plenty of fluid to replace the loss.

  • Some medicines can induce diarrhoea. Please ask your doctor if it is the common side effect of the medication to be taken.

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Communication with your doctor

  • If you have sudden changes in bowel patterns or habits or if the loose stools or stools with blood or mucus, it may be the signal of some serious bowel diseases, and you should consult the doctor as soon as possible.

  • Do not give children laxatives or antidiarrhoeals without doctor’s recommendation.

  • Seek medical advice before using laxatives and antidiarrhoeals if you are pregnant or breastfeeding.

  • Check with your doctor before using laxatives and antidiarrhoeals if you have a bowel condition such as irritable bowel syndrome.

  • Ask your doctor on how to gradually withdraw from laxatives if you are dependent on them.

  • Visit your doctor if your diarrhoea lasts longer than a week, or accompany with persistent vomiting.

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Storage of Laxatives and Antidiarrhoeals

Laxatives and antidiarrhoeals should be kept in a cool and dry place. Unless specified on the label, medicines should not be stored in refrigerators. Furthermore, drugs should be kept properly in places unreachable by children to prevent accidental ingestion.


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Acknowledgement : The Drug Office would like to thank the Professional Development and Quality Assurance (PD&QA) for their valuable contribution to the preparation of this article.

Drug Office
Department of Health
Jan 2018