CDM College Health Education Series

Osmotic laxatives are medicines used to treat constipation. They work by drawing water into the bowel, helping to soften the stool and make it easier to pass.

They are commonly used when lifestyle measures such as extra fluids, fibre and activity have not been enough.

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What Are Osmotic Laxatives?

Osmotic laxatives increase the amount of water in the bowel. This helps:

• Soften hard stools
• Increase stool volume
• Make bowel motions easier to pass
• Reduce straining

They are usually taken by mouth as a powder, liquid, sachet or tablet.

Common examples include macrogol/polyethylene glycol, lactulose, sorbitol, magnesium hydroxide and magnesium citrate.

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When Are They Used?

Osmotic laxatives may be used for:

• Occasional constipation
• Constipation related to low fibre or low fluid intake
• Constipation caused by reduced mobility
• Constipation related to some medicines
• Chronic constipation under medical guidance

They may also be used before some bowel procedures, but only when specifically prescribed.

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How Long Do They Take to Work?

Osmotic laxatives do not usually work immediately.

Many osmotic laxatives take around 2 to 3 days to have an effect.

Some products may work faster, depending on the type, dose and individual response.

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How to Take Them Safely

Follow the instructions on the packet or the dose given by your doctor or pharmacist.

General advice:

• Take the correct dose
• Mix powders or sachets exactly as directed
• Drink enough fluids during the day
• Do not take more than recommended
• Do not use long term unless advised by a healthcare professional

It is important to drink plenty of fluids when taking osmotic laxatives, as they work by drawing water into the bowel.

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Possible Side Effects

Osmotic laxatives are generally well tolerated, but they may cause:

• Bloating
• Wind
• Abdominal cramps
• Nausea
• Loose stools
• Diarrhoea

Healthdirect notes that osmotic laxatives can cause bloating and increased wind.

Stop or reduce the dose and seek advice if diarrhoea becomes troublesome or you feel dehydrated.

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Who Should Seek Advice First?

Speak with a doctor or pharmacist before using osmotic laxatives if you:

• Are pregnant or breastfeeding
• Are giving them to a child
• Are elderly or frail
• Have kidney disease
• Have heart disease
• Have inflammatory bowel disease
• Have severe abdominal pain, vomiting or bloating
• Have blood in the stool
• Have unexplained weight loss
• Have constipation that is new, severe or persistent
• Take regular medicines that may be affected by diarrhoea or dehydration

Some magnesium-containing laxatives may not be suitable for people with kidney problems unless advised by a doctor.

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When to Seek Urgent Medical Help

Seek urgent medical advice if you have constipation with:

• Severe or worsening abdominal pain
• A swollen or hard abdomen
• Vomiting
• Inability to pass wind
• Blood in the stool
• Black stools
• Fever
• Sudden constipation with severe symptoms
• Signs of dehydration, such as dizziness, very dry mouth or passing very little urine

Call Triple Zero (000) in a medical emergency.

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Lifestyle Tips to Help Constipation

Osmotic laxatives work best when combined with healthy bowel habits.

Helpful steps include:

• Drink enough water
• Increase fibre gradually
• Eat fruit, vegetables and wholegrains
• Stay physically active
• Respond to the urge to open your bowels
• Avoid regular straining
• Review constipating medicines with your doctor if needed

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Important Message

Osmotic laxatives can be helpful for constipation, but they should be used correctly. Do not rely on laxatives long term without medical advice, as not all laxatives are safe for prolonged use.

Emergency Warning Signs

Seek urgent medical help if constipation is associated with:

• Severe or worsening abdominal pain
• A swollen, hard or painful abdomen
• Repeated vomiting
• Inability to pass wind
• Blood in the stool or black stools
• Fever or feeling very unwell
• Dizziness, confusion or signs of dehydration
• Sudden constipation with severe symptoms

Call Triple Zero (000) immediately in a medical emergency.

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Disclaimer

This leaflet provides general health education only. It is not a substitute for medical advice, diagnosis or treatment from your doctor, pharmacist or qualified healthcare professional.

Always follow the instructions on the medicine label or the advice given by your healthcare provider. Seek medical advice if symptoms persist, worsen, or if you are unsure whether osmotic laxatives are suitable for you.

In an emergency, call Triple Zero (000).