Laxatives · Gastrointestinal
Polyethylene glycol 3350
PEG 3350 · macrogol · RestoraLAX® · MiraLAX® · Lax-A-Day®(brand names vary by market)
An inert molecule that holds water and does nothing else.
Mechanism
A large, non-absorbed polymer that retains water in the stool by osmosis. It is not fermented by colonic bacteria, which is why it causes far less gas and cramping than lactulose.
Indications
- Constipation
- Faecal impaction
- Bowel preparation at high volume
Formulations
Dosing concepts
Titration
Dosed to stool consistency rather than to a fixed schedule, and it takes one to three days to work fully.
First line
It has the best evidence of the common laxatives for chronic constipation and is the sensible starting point for most patients.
Concepts, not prescribing instructions. Practice numbers live in current references and local protocols.
Pharmacokinetics
- Bioavailability
- Essentially none, which is the point
- Half-life
- Not applicable; acts in the lumen
- Elimination
- plasma: Not absorbed; passes through unchanged
Adverse effects
- Bloating and crampingcommonMuch less than with lactulose because it is not fermented.
- Diarrhoea if over-dosedcommon
- Electrolyte disturbance at bowel-preparation volumesserious
Contraindications & precautions
Contraindications
- Bowel obstruction or perforation
- Toxic megacolon
Precautions
- Renal or cardiac impairment at high volumes
Interactions
No curated interaction entries yet for this agent.
Monitoring
Stool frequency and consistency
The dose is titrated against it
Electrolytes with prolonged high-dose use
Mainly relevant at bowel-preparation volumes
Counselling points
- Mix the powder in a full glass of water or juice and drink it all.
- It takes a day or two to work; do not double the dose on day one.
- Adjust the dose to get a soft, formed stool.
Clinical pearls
- It is the laxative with the strongest evidence base and the mildest side-effect profile, and yet docusate, which repeatedly fails against placebo, is still prescribed more often out of habit.
- It softens stool but does not stimulate propulsion, which is why it is the wrong single answer for opioid constipation.
References & review
- Polyethylene glycol 3350 product monograph (consult the current version for your market) (monograph)
- Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed. (reference-work)
Last reviewed 2026-08-16 · jurisdiction: global · drug information changes; verify against current references before practice use.