The best-evidenced laxative for ordinary constipation — and the one most often taken at too low a dose to work.
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Macrogol is an osmotic laxative. It is a large inert molecule that is not absorbed; it holds water within the stool, softening it and increasing its bulk, which in turn stimulates the bowel to move.
It does not irritate or stimulate the bowel wall, which is why it does not cause the cramping that stimulant laxatives can, and why it is suitable for long-term use.
It is first-line for most constipation in UK practice, including in children and pregnancy.
Most people who say macrogol did not work took one sachet a day for two days and stopped. The dose is titrated to effect — increase it every couple of days until stools are soft and comfortable, then find the maintenance dose that keeps them that way.
After a long period of constipation the bowel needs weeks to recover its tone. Stopping the moment things improve is why constipation so often returns immediately. Treatment is frequently needed for several weeks, then tapered down.
Electrolyte disturbance is possible at high doses, particularly in frail, elderly people or those with heart or kidney disease.
Allergic reactions are rare. Seek urgent help for facial swelling or breathing difficulty.
Caution in significant heart or kidney impairment, where the salt content of higher doses matters.
It is considered suitable in pregnancy and breastfeeding, and is generally the preferred laxative there.
Macrogol can reduce the absorption of other medicines taken at the same time, simply by moving things through faster. Separate other tablets by an hour or two where absorption matters — particularly levothyroxine and antiepileptics.
No routine monitoring for ordinary use.
Electrolytes are worth checking with prolonged high-dose use, in frail older people, and in anyone with kidney or heart disease.
New constipation in an adult over 50, or constipation with weight loss, rectal bleeding or anaemia, needs investigating rather than treating. Thyroid function, calcium and a full blood count are reasonable baseline checks, and an unexplained change in bowel habit warrants FIT testing and referral.
Yes, though macrogol is inexpensive over the counter and rarely needs a prescription for ordinary constipation.
What a consultation adds is the reason for the constipation, which is where most of the value sits.
What we will not do is supply laxatives repeatedly for a change in bowel habit that needs investigating. A prescription is never guaranteed. This page is information, not an offer to supply.
Own-brand macrogol sachets cost a fraction of branded Movicol and are pharmaceutically equivalent. Supermarkets and pharmacies both sell them.
On a private prescription the cost is broadly comparable to the England NHS prescription charge. NHS prescriptions are free in Wales, and free for many people in England.
Do not stop abruptly the moment things improve — that is the commonest reason constipation returns within days.
Continue at an effective dose until stools have been soft and comfortable for a sustained period, then reduce gradually. After long-standing constipation this can take weeks to months, and that is normal rather than a sign of dependence.
The bowel does not become dependent on it, which is a common and unfounded worry that leads people to stop too early. Long-term use is entirely acceptable where it is needed.
Usually one to three days. It is not a stimulant and it will not produce a result within hours — that is a different type of laxative.
Almost always the dose, the water, or the duration. One sachet a day for two days is not a trial. Increase gradually to two or three, dissolve each in a full 125ml, and give it a week.
No. Macrogol is not habit-forming and the bowel does not stop working without it. That worry causes people to stop far too early, which is why the constipation returns.
Yes — it is generally the preferred laxative in pregnancy, because it is not absorbed.
Yes, it is first-line for constipation in children, at doses adjusted for age. Childhood constipation often needs treating for months, and stopping early is the usual reason it recurs.
A new, persistent change in bowel habit over 50, blood in the stool, unexplained weight loss, or constipation with vomiting and severe pain. Those need assessment rather than a laxative.
Separate them by an hour or two, particularly levothyroxine, since macrogol can reduce absorption.
Clinically reviewed by Dr Mohammad Zubair Khan, GMC 7563469
Last reviewed
September 8, 2026
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