Macrogol (polyethylene glycol) !
An inert, non-absorbed polymer that holds water in the bowel and softens stool. Also used, with salts, to clean the colon before colonoscopy.
Updated 2026-11-01
Also called: Polyethylene glycol, PEG 3350, PEG 4000
Mechanism of action
Macrogol is a large, inert polymer that is not absorbed or broken down by colonic bacteria. Its molecules hold water in the bowel by osmosis, so stools become larger, softer and more frequent. Because bacteria do not ferment it, it causes less gas and cramping than lactulose or sorbitol. Bowel-preparation solutions add sodium, potassium, chloride, bicarbonate and sulfate so large volumes cause little net shift of fluid or electrolytes.
- Inert polymer: not absorbed, not fermented
- Holds water in the bowel lumen by osmosis
- Larger, softer stools trigger more frequent bowel movements
Pharmacokinetics
- Absorption
- Essentially not absorbed
- Metabolism
- Not broken down by colonic bacteria
- Elimination
- In the stool
- Onset and duration
- For constipation, a bowel movement usually comes in 1 to 3 days
Indications
- Constipation in adults and children Constipation and faecal impaction →
- Faecal impaction Constipation and faecal impaction →
- Bowel preparation before colonoscopy (with electrolytes)
Adverse effects
Common
- Bloating
- Abdominal pain and cramps
- Flatulence
- Nausea or vomiting
- Diarrhoea
Contraindications
- Allergy to polyethylene glycol
- Known or suspected bowel obstruction
- Kidney disease without medical supervision
Key interactions
- Starch-based thickeners for swallowing problems
- The label warns against combining them; patients who need thickened liquids are given a different plan
- Other oral medicines
- Faster transit can reduce their absorption; they are usually given at least an hour apart
What is monitored
- Stool frequency and consistency
- Diarrhoea, which signals an excessive dose
- Fluid and electrolyte balance in heart or kidney disease and during bowel preparation
Administration and safety
- The powder is fully dissolved in a drink before it is taken; it is not swallowed with clumps.
- Not mixed with starch-based thickeners used in dysphagia.
- During bowel preparation the patient keeps drinking clear fluids to stay hydrated.
Nursing care
- Check for signs of bowel obstruction (vomiting, distension, severe pain) before starting.
- Record stool output and report diarrhoea.
- In bowel preparation, watch for dizziness, weakness and dehydration, especially in older adults.
- Teach to space other medicines from the dose and to report rectal bleeding.
Pregnancy and breastfeeding
Considered suitable in pregnancy and breastfeeding because it is barely absorbed.
Test yourself
Think of the answer, then tap the question to see it.
Why does macrogol cause less gas than lactulose?
Colonic bacteria do not ferment it, so little gas is produced.
Why are electrolytes added to macrogol bowel-preparation solutions?
So that large volumes clean the colon without causing important net shifts of fluid or electrolytes.
Which swallowing aid should not be mixed with macrogol?
Starch-based thickeners used in dysphagia; the product label warns against combining them.
Related drugs
Related conditions
← Back to the class: Laxatives
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - POLYETHYLENE GLYCOL 3350 powder, for solution (DailyMed (U.S. National Library of Medicine), 2026); Polyethylene Glycol 3350: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2016); Macrogol: a laxative medicine to treat constipation - NHS (NHS (National Health Service, UK), 2026); Farmacología básica y clínica (Katzung), 16.ª ed., cap. 62 (McGraw Hill, 2025).
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