Macrogol (PEG): Uses, Dosage & Side Effects

What Is Macrogol (PEG) and What Is It Used For?

Macrogol (polyethylene glycol 4000) is an osmotic laxative that works by retaining water in the intestinal lumen, increasing stool volume and softness, and stimulating natural bowel movements. It is used to treat constipation in adults, children from 6 months of age, and elderly patients. Macrogol is not absorbed into the bloodstream and is not metabolized, giving it an excellent safety profile.

Macrogol belongs to the pharmacological class of osmotic laxatives and is classified under ATC code A06AD15. The active substance is a long-chain linear polymer of ethylene oxide, commonly referred to as polyethylene glycol (PEG) with an average molecular weight of 4000 daltons. This specific molecular weight ensures optimal water retention in the intestinal lumen without significant absorption through the gut wall. Macrogol has been used in clinical practice since the 1990s and is included on the WHO Model List of Essential Medicines as a recommended treatment for constipation.

The mechanism of action of macrogol is elegantly simple. Each macrogol molecule forms hydrogen bonds with a large number of surrounding water molecules, effectively trapping water in the intestinal lumen. This osmotic effect increases the fluid content and volume of stool, making it softer and easier to pass. The increased stool volume also gently stretches the bowel wall, which triggers the natural peristaltic reflex – the wave-like muscle contractions that move stool through the intestines. Unlike stimulant laxatives (such as bisacodyl or senna), macrogol does not directly stimulate or irritate the nerve endings in the bowel wall. This means it does not cause the cramping and urgency commonly associated with stimulant laxatives, and it does not lead to habituation or bowel damage with long-term use.

A key pharmacological advantage of macrogol is that it is biologically inert. It is not absorbed from the gastrointestinal tract, is not broken down by intestinal bacteria, and is not metabolized by the liver or any other organ. The entire dose passes through the digestive system unchanged and is eliminated in the faeces. This property means that macrogol does not enter the systemic circulation and therefore has no systemic side effects, drug metabolism interactions, or organ toxicity. It also means it is safe for use in patients with liver or kidney impairment, though caution is still advised regarding electrolyte balance in these populations.

Macrogol is approved and commonly used for the following indications:

• Chronic constipation – the primary indication, providing gentle and effective relief of constipation in adults and children by increasing stool water content and volume
• Paediatric constipation – macrogol is one of the first-line treatments recommended by NICE and ESPGHAN guidelines for constipation in children from 6 months of age, as it is effective, well-tolerated, and does not cause the abdominal cramping associated with stimulant laxatives
• Fecal impaction – at higher doses under medical supervision, macrogol combined with electrolytes is used to disimpact hardened stool in children and adults, often as an alternative to enemas
• Bowel preparation – higher-volume macrogol solutions (typically macrogol 3350 with electrolytes) are used for bowel cleansing before colonoscopy, surgery, or radiological examinations
• Opioid-induced constipation – macrogol is frequently used alongside opioid analgesics to manage the constipation that commonly occurs as a side effect of opioid therapy

It is important to understand that macrogol treats the symptom of constipation but does not address underlying causes. Chronic constipation can result from inadequate dietary fibre, insufficient fluid intake, a sedentary lifestyle, certain medications (including opioids, iron supplements, calcium channel blockers, and anticholinergics), or underlying medical conditions such as hypothyroidism, irritable bowel syndrome, or neurological disorders. A comprehensive approach to managing constipation should always include lifestyle modifications – increasing dietary fibre, drinking adequate fluids, and engaging in regular physical activity – alongside any pharmacological treatment.

What Should You Know Before Taking Macrogol?

Before taking macrogol, be aware that it must not be used if you have intestinal obstruction or perforation, severe inflammatory bowel disease (such as ulcerative colitis, Crohn's disease, or toxic megacolon), or unexplained abdominal pain. Macrogol is safe during pregnancy and breastfeeding as it is not absorbed. Patients with kidney impairment or those taking diuretics should consult their doctor before use.

Macrogol is widely regarded as a safe and well-tolerated laxative, but like all medicines, it is not suitable for everyone. Understanding the situations in which macrogol should not be used, and the precautions that apply to specific patient groups, is essential for safe and effective treatment. The most important principle is that constipation accompanied by warning signs – such as unexplained weight loss, rectal bleeding, a sudden change in bowel habits in adults over 50, or severe abdominal pain – should always be evaluated by a doctor before starting any laxative treatment.

Contraindications

You must not take macrogol if any of the following apply:

• Allergy to macrogol (polyethylene glycol) or any other ingredient in the product – while rare, allergic reactions including anaphylaxis have been reported with macrogol-containing products
• Intestinal obstruction (bowel blockage) or suspected intestinal obstruction – macrogol increases stool volume, which could worsen a mechanical bowel obstruction and lead to perforation
• Intestinal perforation or risk of perforation – any condition that has weakened the bowel wall makes the use of osmotic laxatives potentially dangerous
• Severe inflammatory bowel disease – including active ulcerative colitis, Crohn's disease with strictures, or toxic megacolon (abnormal dilation of the colon)
• Unexplained abdominal pain – abdominal pain of unknown origin should be investigated before starting laxative treatment, as it may indicate a surgical condition

Warnings and Precautions

Speak to your doctor or pharmacist before taking macrogol in the following situations:

Organic disease should be excluded: Before starting macrogol therapy, especially in children, your doctor should ensure that the constipation is not caused by an underlying organic disease (such as Hirschsprung disease in infants or a bowel tumour in adults). If constipation does not respond to treatment within 2 weeks, seek medical review.

Diarrhoea risk: Macrogol can cause diarrhoea, particularly if the dose is too high. If diarrhoea develops, reduce the dose or temporarily stop treatment. Prolonged or severe diarrhoea can lead to dehydration and electrolyte disturbances, particularly loss of sodium and potassium. This is especially important in young children, elderly patients, and those with impaired kidney function.

Kidney impairment and diuretic use: Patients with reduced kidney function or those taking diuretics (water tablets) are at increased risk of developing low sodium (hyponatraemia) or low potassium (hypokalaemia) if macrogol causes significant diarrhoea. Your doctor should monitor electrolyte levels if you are in these groups and require prolonged macrogol treatment.

Swallowing difficulties: If you or your child has difficulty swallowing (dysphagia), discuss this with your doctor before taking macrogol. Do not mix macrogol with starch-based thickeners used for dysphagia management, as macrogol can break down the starch and result in a thin, watery consistency that may be aspirated into the lungs, potentially causing aspiration pneumonia.

Pregnancy and Breastfeeding

Constipation is one of the most common gastrointestinal complaints during pregnancy, affecting up to 40% of pregnant women. The hormonal changes of pregnancy (particularly increased progesterone) slow intestinal transit, and iron supplements prescribed during pregnancy often worsen constipation.

Pregnancy: Macrogol is generally considered safe during pregnancy because it is not absorbed into the bloodstream. It is not expected to affect the developing baby in any way. Many clinical guidelines, including those from NICE and the American College of Obstetricians and Gynecologists (ACOG), recommend macrogol as a first-line pharmacological treatment for constipation in pregnancy when lifestyle measures alone are insufficient. However, as with all medicines during pregnancy, you should consult your doctor or midwife before starting treatment.

Breastfeeding: Macrogol is not absorbed from the gastrointestinal tract and therefore cannot pass into breast milk. It is considered safe to use during breastfeeding. No dose adjustment is required.

Driving and Operating Machinery

Macrogol has no known effect on the ability to drive or operate machinery. No studies on driving ability have been conducted, but given that macrogol is not absorbed and has no systemic effects, impairment of these abilities is not expected.

How Does Macrogol Interact with Other Drugs?

Macrogol may temporarily reduce the absorption of other medicines taken at the same time, particularly drugs with a narrow therapeutic index or short half-life such as digoxin, anti-epileptic drugs, coumarins (warfarin), and immunosuppressants (ciclosporin, tacrolimus, mycophenolate). This reduced absorption can lead to decreased effectiveness of these medicines. To minimize this risk, take other medicines at least 2 hours before or after macrogol.

Because macrogol is not absorbed from the gastrointestinal tract and is not metabolized by the body, it does not interact with other medicines through the typical pharmacokinetic pathways (such as enzyme induction or inhibition). However, macrogol exerts its laxative effect by increasing the fluid content in the intestines, and this increased fluid volume can dilute and accelerate the transit of other medicines taken around the same time. This means that co-administered drugs may have less time in contact with the absorptive surface of the intestine, potentially reducing their bioavailability. This effect is most clinically significant for medicines with a narrow therapeutic window – that is, drugs where even small changes in blood levels can result in loss of efficacy or toxicity.

Clinically Significant Interactions

The following medicines require particular attention when used concurrently with macrogol:

Other Important Interactions

The following interactions are also worth noting:

What Is the Correct Dosage of Macrogol?

The recommended dose of macrogol depends on the patient's age and the formulation used. For paediatric constipation (4 g sachets): children 6 months to 1 year take 1 sachet per day; children 1–4 years take 1–2 sachets per day; children 4–8 years take 2–4 sachets per day. For adult constipation, typical doses are 1–3 sachets per day of adult-strength product. Dissolve each sachet in water and drink immediately. The effect typically occurs within 24–48 hours.

The correct dosage of macrogol varies depending on the patient's age, the severity of constipation, and whether the product is a paediatric formulation (typically 4 g macrogol per sachet) or an adult formulation (typically 13.125 g macrogol per sachet, often combined with electrolytes). Always follow the instructions on the product packaging or your doctor's specific prescription. The following dosing guidelines are based on international prescribing information and clinical guidelines.

Children (Paediatric Macrogol 4 g Sachets)

Macrogol is approved for children from 6 months of age for the treatment of constipation. Paediatric formulations contain a lower dose of macrogol (typically 4 g per sachet) and are designed to be mixed in a smaller volume of water for easier administration.

Adults and Adolescents

Adult macrogol formulations typically contain a higher dose per sachet (13.125 g macrogol, often combined with electrolytes including sodium chloride, sodium bicarbonate, and potassium chloride) and are dissolved in a larger volume of water.

Elderly Patients

No specific dose adjustment is required for elderly patients. However, older adults are more susceptible to fluid and electrolyte disturbances, particularly if they have reduced kidney function or are taking diuretics. Start with the lowest recommended dose and adjust based on response. Ensure adequate fluid intake during treatment. If macrogol causes significant diarrhoea, reduce the dose or temporarily stop treatment and consult a doctor.

How to Prepare and Take Macrogol

1. Open the sachet and pour the entire contents into a glass
2. Add the appropriate amount of water (50 ml for paediatric sachets, 125 ml for adult sachets)
3. Stir well until the powder is completely dissolved – the solution should be clear or slightly cloudy
4. Drink the solution immediately after preparation
5. If the prepared solution cannot be drunk immediately, it can be stored covered in the refrigerator (2–8°C) for up to 6 hours

Missed Dose

If you forget to take a dose of macrogol, take it as soon as you remember. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. Missing a single dose is unlikely to significantly affect treatment, as macrogol works cumulatively over days rather than producing an immediate effect from each individual dose.

Overdose

Taking too much macrogol typically causes diarrhoea, abdominal pain, or vomiting. The diarrhoea usually resolves when the dose is reduced or treatment is temporarily stopped.

What Are the Side Effects of Macrogol?

Common side effects of macrogol include abdominal pain, diarrhoea, and bloating. In children, perianal soreness may occur as a result of more frequent bowel movements. Serious side effects are rare but include allergic reactions (rash, urticaria, angioedema, anaphylaxis) and electrolyte disturbances (low sodium or potassium) in susceptible patients. Most side effects are mild, dose-related, and resolve with dose reduction.

Like all medicines, macrogol can cause side effects, although not everyone experiences them. Macrogol has an excellent overall safety profile because it is not absorbed into the body. Most adverse effects are related to its laxative action and are dose-dependent – meaning they can usually be managed by reducing the dose. The following frequency classification is based on clinical trial data and post-marketing surveillance reports.

Stop taking macrogol and seek emergency medical care immediately if you experience any of the following serious symptoms:

• Swelling of the face, tongue, or throat; difficulty breathing; hives combined with dizziness or collapse (signs of anaphylaxis or angioedema)
• Severe abdominal pain that does not improve, especially with vomiting and inability to pass gas or stool (possible intestinal obstruction)
• Signs of severe dehydration: extreme thirst, very dark urine, dizziness on standing, rapid heartbeat, or confusion

Side Effects in Children

Side Effects in Adults

If you experience any side effects while taking macrogol, particularly any serious or unexpected symptoms not listed above, report them to your healthcare provider. Reporting suspected adverse reactions after a medicine has been authorized helps ongoing monitoring of its benefit-risk balance. In many countries, patients and healthcare professionals can report side effects directly to the national pharmacovigilance authority (for example, the MHRA Yellow Card scheme in the UK, MedWatch in the US, or EudraVigilance in the EU).

How Should You Store Macrogol?

Store macrogol sachets at room temperature in a dry place. No special temperature requirements apply. Keep out of sight and reach of children. Do not use after the expiry date on the packaging. Prepared solution can be stored in the refrigerator (2–8°C) for up to 6 hours if not consumed immediately.

Proper storage of macrogol ensures the powder remains effective and safe throughout its shelf life. Follow these guidelines:

• Packaging: Store in the original packaging. The sachets protect the powder from moisture, which can cause it to clump or dissolve prematurely
• Temperature: No special storage temperature is required. Store at room temperature and keep away from excessive heat or humidity
• Children: Keep out of the sight and reach of children at all times
• Expiration: Do not use after the expiry date (month/year) printed on the carton and sachets. The expiry date refers to the last day of that month
• Prepared solution: If you prepare the macrogol solution but cannot drink it immediately, store it well covered in the refrigerator (2–8°C) and consume within 6 hours

Disposal: Do not dispose of medicines via wastewater or household waste. Return unused or expired macrogol to your local pharmacy for safe disposal. These measures help protect the environment.

What Does Macrogol Contain?

The active substance is macrogol 4000 (polyethylene glycol). Paediatric sachets contain 4 g of macrogol 4000 per sachet. Adult sachets typically contain 13.125 g of macrogol 3350 or 4000, often combined with electrolytes (sodium chloride, sodium bicarbonate, potassium chloride). Inactive ingredients vary by brand but commonly include saccharin sodium, flavouring agents (such as orange-grapefruit aroma), sorbitol, and acacia gum.

Macrogol is available in several formulations to suit different patient populations and clinical needs:

Paediatric sachet excipients (e.g., Omnilax, Lacrofarm Junior): saccharin sodium (E954), flavouring (orange-grapefruit aroma containing maltodextrin, sorbitol (E420), butylhydroxyanisole (E320), and acacia gum (E414)). The powder is off-white and produces an orange-grapefruit flavoured drink when dissolved.

Adult sachet excipients vary by brand. Common brands include:

• Moxalole / Laxido: Macrogol 3350 with sodium chloride, sodium bicarbonate, and potassium chloride; available in orange or unflavoured varieties
• Makrogol EQL: Macrogol 4000 without electrolytes
• MiraLAX / ClearLax / GlycoLax (available OTC in some countries): Macrogol 3350 without electrolytes; powder that can be dissolved in any clear beverage

Available pack sizes: Macrogol is commonly available in packs of 10, 20, 30, or 50 sachets. Not all pack sizes may be marketed in all countries.

Sodium content: Most macrogol formulations contain less than 1 mmol (23 mg) sodium per sachet for the paediatric product, making them essentially sodium-free. Adult products with electrolytes contain slightly more sodium but are still considered low-sodium medicines.