Polyethylene Glycol 3350

What it is

Polyethylene glycol 3350 is a synthetic polymer, a long chain of repeating ethylene glycol units. It is a white powder that dissolves in water and is swallowed as a drink. It is absorbed in only trace amounts from the gut, so it works inside the bowel rather than in the bloodstream. The same molecule is sold in two very different products: a 17 g once-daily over-the-counter powder for constipation, and a 4 litre prescription solution with added salts for cleaning the bowel before a colonoscopy.

What the research says

The evidence here is consistent in direction but weak in quality. PEG 3350 holds water in the colon, which softens stool and increases how often people pass it. Cochrane found that against placebo in children it added about 2.6 stools a week, and that it beat lactulose both in children and in adults. But the same Cochrane review rated its own primary-outcome evidence low or very low certainty because the trials were sparse, short and often unblinded. The common harms are gut symptoms, flatulence, abdominal pain, nausea, diarrhoea and headache. The uncommon serious harm is allergy, including anaphylaxis, which the FDA adverse event database records for PEG 3350. The bowel-preparation product carries extra risks that the small daily dose does not: electrolyte disturbances, seizures, arrhythmias and ischaemic colitis.

Evidence grade: Well established.

How it works

Drug class: Osmotic laxative (polyethylene glycol polymer)

PEG 3350 is a large molecule that the gut barely absorbs. Each unit binds water by hydrogen bonding, so the water it is dissolved in stays in the bowel instead of being reabsorbed. That extra water softens the stool and increases its bulk, which triggers the normal stretch reflexes that move it along. Nothing enters the bloodstream in a meaningful amount, which is why it has few whole-body effects at laxative doses. (Source 1)

What it is used for

• The OTC label's claim is modest and matches the trials: it relieves occasional constipation and generally produces a bowel movement in one to three days. In a 156-patient placebo-controlled trial, PEG3350 plus electrolytes increased spontaneous bowel movements significantly more than placebo over two weeks (least-squares mean change from baseline 4.3 versus 1.6). Evidence: established. (Source 2)
• Approved for this purpose and it works, with diarrhoea that usually clears the bowel within about four hours. The trade-off is that nausea, fullness and bloating occur in up to 50 percent of patients and rare serious events include seizures, arrhythmias, ischaemic colitis and aspiration. Evidence: established. (Source 3)
• The US OTC label tells anyone 16 or under to ask a doctor, so paediatric use is outside the OTC labelling, yet it is one of the best-studied uses. Cochrane pooled 25 randomised trials and found PEG better than placebo, lactulose and milk of magnesia, but rated the certainty of the primary outcome low or very low. Evidence: limited. (Source 4)
• The OTC label says not to use it for more than seven days. A Japanese phase III trial continued PEG3350 plus electrolytes for 52 weeks with sustained benefit and mostly mild gut side effects, but it is one trial in one population. Evidence: limited. (Source 4)
• A 2024 Cochrane review of intractable childhood constipation included one 52-week trial using 0.5 g/kg/day PEG as the comparator and rated the comparison very low certainty, concluding that no robust conclusions could be drawn for most comparisons. Evidence: unknown. (Source 5)

Interactions

• Starch-based thickeners used for swallowing difficulty (label): PEG thins starch-thickened drinks. When a PEG product was mixed into starch-thickened liquids for people with dysphagia, the liquid thinned and choking and potential aspiration were reported. Both the OTC and prescription labels now say not to combine them. (Source 4)
• Any other oral medicine taken at the same time (label): The bowel preparation washes drugs through before they can be absorbed. The label says to take oral medicines within one hour before starting the preparation. (Source 6)
• Stimulant laxatives such as bisacodyl or sodium picosulfate (label): Taking a stimulant laxative alongside the PEG bowel preparation may increase the risk of bowel lining ulceration or ischaemic colitis; the label says to avoid the combination. (Source 6)
• Diuretics, ACE inhibitors, angiotensin receptor blockers and NSAIDs (label): These all affect kidney function or fluid balance, so combining them with the PEG bowel preparation raises the risk of kidney impairment; the label advises adequate hydration and baseline and post-procedure electrolytes, creatinine and BUN. (Source 7)
• Alcohol or benzodiazepine withdrawal, and tricyclic antidepressants (label): Bowel preparation has caused seizures in people with no seizure history. The label singles out people taking medicines that lower the seizure threshold such as tricyclic antidepressants, people withdrawing from alcohol or benzodiazepines, and people with suspected low sodium as being at higher risk. (Source 8)
• Polysorbate 80 (an emulsifier in many supplements, foods and injectables) (case reports): People allergic to PEG 3350 can cross-react to polysorbate 80. In the two cases studied, skin and provocation testing showed symptomatic reactivity to both, and anti-PEG IgE and IgG were detectable. (Source 9)
• Polyethylene glycol itself, as an excipient in other products (label): PEG is in thousands of medicines, supplements and cosmetics, so someone allergic to the laxative can react to unrelated products. The OTC label's allergy alert is simply not to use it if you are allergic to polyethylene glycol. (Source 10)
• Other drugs taken by mouth while on daily PEG (label): The prescription label states PEG reduces absorption of co-administered drugs; the mechanism is dilution and faster transit, and the same principle applies in a smaller way to daily laxative doses, though this has not been quantified for the 17 g dose. (Source 6)

Stopping it

• PEG 3350 does not cause dependence and no withdrawal syndrome is described for it. The over-the-counter label's stopping rule is driven by duration and symptoms rather than tapering. Under the heading 'Stop use and ask a doctor if', it lists rectal bleeding or worsening nausea, bloating, cramping or abdominal pain; getting diarrhoea; and needing a laxative for longer than 1 week. Those are reasons to stop and seek advice, not permission to continue. The label itself contains two printing mistakes in this panel - 'Ask a doctor of pharmacist' and 'or you nausea' - which are the manufacturer's and are reproduced here exactly as printed. (Source 10)
• Stopping is also indicated if new alarm symptoms appear. The label's 'Stop use and ask a doctor if' list includes rectal bleeding, or worsening nausea, bloating, cramping or abdominal pain, which it says may be signs of a serious condition. The wording 'or you nausea' is a printing mistake in the label itself; it means 'or your nausea'. (Source 10)
• Long-term continuous use has been studied rather than being assumed harmful. A 52-week open-label extension of a placebo-controlled trial reported sustained improvement in bowel function, with adverse drug reactions limited mostly to mild gut symptoms (abdominal pain 4.5%, diarrhoea 3.8%, nausea 3.2%, abdominal distension 2.6%). (Source 11)

What goes wrong

In the placebo-controlled paediatric trials the common side effects were gut symptoms and headache. (Source 12)

• Systematic review, Low certainty.
• Size: 101 participants in the placebo-controlled comparison.
• Who: Children with functional constipation.
• How long: Short follow-up.
• Result: No rates given; the review lists flatulence, abdominal pain, nausea, diarrhoea and headache as common. No serious adverse events were reported in the PEG versus lactulose trials, and one child was allergic to PEG.
• Funding: not stated in the record fetched.

Common adverse events in the placebo-controlled studies included flatulence, abdominal pain, nausea, diarrhoea and headache.

Nausea, fullness and bloating affect up to half of people taking the 4 litre bowel-preparation version. (Source 13)

• Official position, Certainty not rated.
• Size: Not quantified beyond the rate given.
• Who: Adults undergoing bowel cleansing before colonoscopy.
• How long: A single preparation.
• Result: Nausea, abdominal fullness and bloating in up to 50% of patients; less common reactions include cramps, vomiting, anal irritation, Mallory-Weiss tear bleeding and oesophageal perforation.
• Funding: US regulatory document.

Nausea, abdominal fullness and bloating are the most common adverse reactions (occurred in up to 50% of patients).

Serious hypersensitivity including anaphylaxis is listed for the PEG bowel preparation. (Source 13)

• Official position, Certainty not rated.
• Size: Spontaneous reports; frequency cannot be estimated.
• Who: Adults using PEG-3350 with electrolytes.
• How long: Single use.
• Result: Urticaria, rash, pruritus, dermatitis, rhinorrhoea, dyspnoea, chest and throat tightness, fever, angioedema, anaphylaxis and anaphylactic shock; no rates given.
• Funding: US regulatory document.

Hypersensitivity: Urticaria/rash, pruritus, dermatitis, rhinorrhea, dyspnea, chest and throat tightness, fever, angioedema, anaphylaxis and anaphylactic shock

In two patients studied in detail, immediate allergy to PEG 3350 was confirmed by skin and provocation testing and was associated with anti-PEG antibodies, and an FDA database search found 53 further reports of possible PEG 3350 anaphylaxis. (Source 9)

• Case series, Very low certainty.
• Size: 2 index cases plus 6 PEG-3350-tolerant controls, plus 53 FDA adverse event reports.
• Who: Adults with a history of immediate hypersensitivity to PEG-containing medicines.
• How long: Not applicable.
• Result: Both cases reacted to PEG 3350 and to polysorbate 80 on skin and provocation testing; anti-PEG IgE and IgG were positive only in the cases and binding rose with PEG molecular weight.
• Funding: not stated in the record fetched; PubMed indexes it as Research Support, N.I.H., Extramural.

Limit of this finding: The mechanistic result rests on two patients and six PEG-3350-tolerant controls, so it shows that this allergy exists and can be detected, not how common it is. The 53 further cases are spontaneous reports to the FDA that the authors describe as 'possible' anaphylaxis; they were not individually confirmed, so they should not be counted as 53 proven reactions.

FDA adverse event reports revealed 53 additional cases of possible PEG 3350 anaphylaxis.

Bowel-preparation PEG can cause fluid and electrolyte disturbances severe enough to lead to arrhythmias, seizures and kidney impairment. (Source 14)

• Official position, Certainty not rated.
• Size: Not quantified.
• Who: Adults undergoing bowel preparation, especially with heart failure, kidney impairment or arrhythmia risk.
• How long: Single preparation.
• Result: Rare reports of serious arrhythmias with ionic osmotic laxative bowel preparations; the label directs correcting abnormalities before use and considering post-colonoscopy electrolytes, creatinine and BUN.
• Funding: US regulatory document.

Fluid and electrolyte disturbances can lead to serious adverse events including cardiac arrhythmias, seizures and renal impairment.

Generalised tonic-clonic seizures and loss of consciousness have been reported with bowel preparation products in people with no prior seizure history. (Source 8)

• Official position, Certainty not rated.
• Size: Not quantified.
• Who: Adults undergoing bowel preparation.
• How long: Single preparation.
• Result: Associated with hyponatraemia, hypokalaemia, hypocalcaemia and hypomagnesaemia and low serum osmolality; the neurological abnormalities resolved when the electrolytes were corrected.
• Funding: US regulatory document.

There have been reports of generalized tonic-clonic seizures and/or loss of consciousness associated with use of bowel preparation products in patients with no prior history of seizures.

Osmotic laxative bowel preparations can produce colonic ulceration and, more seriously, ischaemic colitis needing hospital admission. (Source 15)

• Official position, Certainty not rated.
• Size: Not quantified.
• Who: Adults undergoing bowel preparation, risk increased by concurrent stimulant laxatives.
• How long: Single preparation.
• Result: No rates given; the label warns these ulcerations can be mistaken for inflammatory bowel disease at colonoscopy.
• Funding: US regulatory document.

Administration of osmotic laxative products may produce colonic mucosal aphthous ulcerations, and there have been reports of more serious cases of ischemic colitis requiring hospitalization.

Mixing PEG with starch-based thickeners thins the liquid and has caused choking and potential aspiration. (Source 16)

• Official position, Certainty not rated.
• Size: Not quantified; reported cases.
• Who: People with swallowing difficulty using starch-thickened drinks.
• How long: Not applicable.
• Result: No rates given; both the prescription and the over-the-counter labels now instruct against combining PEG with starch-based thickeners.
• Funding: US regulatory document.

when mixed with starch-thickened liquids reduces the viscosity of the starch-thickened liquid. When a PEG-based product used for another indication was mixed in starch-based pre-thickened liquids used in patients with dysphagia, thinning of the liquid occurred and cases of choking and potential aspiration were reported.

What the evidence supports

Against placebo in children, PEG increased the number of stools per week, but on only two small trials. (Source 12)

• Systematic review, Low certainty.
• Size: 101 patients in 2 randomised trials (25 RCTs and 2,310 participants in the whole review)
• Who: Children aged 0 to 18 with functional constipation.
• How long: Short; the review notes follow-up was short across comparisons.
• Result: Mean difference 2.61 stools per week (95% CI 1.15 to 4.08) favouring PEG.
• Funding: not stated in the record fetched.

Meta-analysis of two studies (101 patients) comparing polyethylene glycol (PEG) with placebo showed a significantly increased number of stools per week with PEG (MD 2.61 stools per week, 95% CI 1.15 to 4.08).

PEG produced more stools per week than lactulose and fewer children needed an additional laxative. (Source 12)

• Systematic review, Low certainty.
• Size: 465 participants in 6 trials for stool frequency; 304 participants for additional therapies.
• Who: Children with functional constipation.
• How long: Short follow-up.
• Result: Stools per week mean difference 0.70 (95% CI 0.10 to 1.31); additional therapies needed by 18% (27/154) on PEG versus 31% (47/150) on lactulose, RR 0.55 (95% CI 0.36 to 0.83), an absolute difference of about 13 percentage points.
• Funding: not stated in the record fetched.

Eighteen per cent (27/154) of PEG patients required additional therapies compared to 31% (47/150) of lactulose patients (RR 0.55, 95% CI 0.36 to 0.83).

A separate Cochrane review of all ten trials comparing lactulose with PEG in chronic constipation favoured PEG, except that the advantage on abdominal pain did not hold for adults and children separately. (Source 17)

• Systematic review, Low certainty.
• Size: 10 randomised controlled trials.
• Who: Adults and children with chronic constipation or faecal impaction.
• How long: Not stated in the record fetched.
• Result: Reported as better on stool frequency per week, form of stool and need for additional products in both adults and children; the advantage on relief of abdominal pain did not hold on subgroup analysis. No pooled effect sizes, confidence intervals or certainty ratings are given in the abstract, and the review dates from 2010.
• Funding: not stated in the record fetched.

The findings of our work indicate that Polyethylene glycol is better than lactulose in outcomes of stool frequency per week, form of stool, relief of abdominal pain and the need for additional products. On subgroup analysis, this is seen in both adults and children, except for relief of abdominal pain.

A higher PEG dose produced more stools than a lower one in a single dose-ranging trial. (Source 12)

• Randomized trial, Low certainty.
• Size: 90 participants in 1 trial.
• Who: Children with functional constipation.
• How long: Not stated in the record fetched.
• Result: 0.7 g/kg versus 0.3 g/kg: mean difference 1.30 stools per week (95% CI 0.76 to 1.84)
• Funding: not stated in the record fetched.

Participants receiving high dose PEG (0.7 g/kg) had significantly more stools per week than low dose PEG (0.3 g/kg) participants (1 study, 90 participants, MD 1.30, 95% 0.76 to 1.84).

A placebo-controlled phase III trial in Japanese adults found PEG3350 plus electrolytes increased spontaneous bowel movements significantly more than placebo over two weeks, with mostly mild gut side effects over the following year. (Source 11)

• Randomized trial, Moderate certainty.
• Size: 156 patients randomised and analysed (204 consented); 153 entered the 52-week extension.
• Who: Japanese adults with chronic constipation.
• How long: 2 weeks double-blind, then a 52-week open-label extension.
• Result: Primary endpoint, the change from baseline in frequency of spontaneous bowel movements at week 2: least-squares mean 4.3 (95% CI 3.6-4.9) with PEG3350+E versus 1.6 (95% CI 1.2-2.1) with placebo, P < 0.0001. Adverse drug reactions over the whole study: abdominal pain 4.5%, diarrhoea 3.8%, nausea 3.2%, abdominal distension 2.6%.
• Funding: not stated in the record fetched; registered as Japic CTI-163167.

Limit of this finding: The 4.3 and 1.6 are least-squares means for the trial's stated primary endpoint, the change from baseline in spontaneous bowel movements at week 2 - not absolute counts of bowel movements, and the abstract gives no time period for them. So they cannot be read as a ratio of bowel-movement frequency, and 4.3 against 1.6 is about 2.7 times, not three times, even taken at face value.

The primary efficacy endpoint was the change from baseline in frequency of spontaneous bowel movements (SBMs) at week 2 in the double-blind study. Secondary endpoints and adverse events were assessed. Safety and efficacy were also assessed in the extension study. RESULTS: Among 204 patients who provided informed consent, 156 were randomized and included in the full analysis. The frequency of SBMs was significantly higher with PEG3350 + E [least squares mean (LSM) 4.3, 95% confidence interval (CI) 3.6-4.9] compared with placebo (LSM 1.6, 95% CI 1.2-2.1; P < 0.0001).

A meta-analysis in children found PEG achieved disimpaction more often than non-PEG laxatives and was better accepted, with the authors calling for better trials of dose and regimen. (Source 18)

• Meta-analysis, Low certainty.
• Size: 10 studies included from 231 articles screened.
• Who: Children with constipation or faecal impaction.
• How long: Not stated in the record fetched.
• Result: No pooled effect sizes are reported in the abstract; the direction favoured PEG on successful disimpaction and on children's acceptance, and the authors state that optimal dosages, routes and regimens still need to be determined in future randomised studies.
• Funding: not stated in the record fetched.

Patients who were treated with PEG experienced more successful disimpaction compared with those treated with non-PEG laxatives. Treatment-related adverse events were acceptable and generally well tolerated. PEG-based laxatives are effective and safe for chronic constipation and for resolving fecal impaction in children. Children's acceptance of PEG-based laxatives appears to be better than non-PEG laxatives. Optimal dosages, routes of administration, and PEG regimens should be determined in future randomized controlled studies and meta-analyses.

What the evidence does not support

PEG was NOT better than enemas, dietary fibre, liquid paraffin or flixweed on stool frequency. (Source 19)

• Systematic review, Low certainty.
• Size: Between 83 and 261 patients per comparison.
• Who: Children with functional constipation.
• How long: Short follow-up.
• Result: PEG versus enemas MD 1.00 (95% CI -1.58 to 3.58); PEG versus flixweed MD 0.00 (95% CI -0.33 to 0.33); PEG versus dietary fibre MD 0.20 (95% CI -0.64 to 1.04); PEG versus liquid paraffin MD 0.35 (95% CI -0.24 to 0.95)
• Funding: not stated in the record fetched.

No statistically significant differences in the number of stools per week were found between PEG and enemas (1 study, 90 patients, MD 1.00, 95% CI -1.58 to 3.58), dietary fibre mix and lactulose (1 study, 125 patients, P = 0.481), senna and lactulose (1 study, 21 patients, P > 0.05), lactitol and lactulose (1 study, 51 patients, MD -0.80, 95% CI -2.63 to 1.03), hydrolyzed guar gum and lactulose (1 study, 61 patients, MD 1.00, 95% CI -1.80 to 3.80), PEG and flixweed (1 study, 109 patients, MD 0.00, 95% CI -0.33 to 0.33), PEG and dietary fibre (1 study, 83 patients, MD 0.20, 95% CI -0.64 to 1.04), and PEG and liquid paraffin (2 studies, 261 patients, MD 0.35, 95% CI -0.24 to 0.95).

In intractable childhood constipation, a trial using PEG as the comparator gave a very low certainty result and no robust conclusion. (Source 5)

• Systematic review, Very low certainty.
• Size: 102 children in that comparison (1,278 children across 10 RCTs in the review)
• Who: Children with functional constipation not responding to conventional therapy.
• How long: 52 weeks.
• Result: Enemas versus 0.5 g/kg/day PEG for treatment success RR 1.33 (95% CI 0.83 to 2.14), very low certainty, downgraded for risk of bias and imprecision.
• Funding: not stated in the record fetched.

One study compared three-weekly rectal sodium dioctyl sulfosuccinate and sorbitol enemas (n = 51) to 0.5 g/kg/day polyethylene glycol laxatives (n = 51) over a 52-week period. We are very uncertain whether rectal sodium dioctyl sulfosuccinate and sorbitol enemas improve treatment success (RR 1.33, 95% CI 0.83 to 2.14; very low certainty evidence, downgraded due to serious concerns with risk of bias and imprecision).

The widely circulated concern that PEG 3350 loads children with antifreeze chemicals was tested and not supported. (Source 20)

• Blood level study, Low certainty.
• Size: 9 children treated with PEG 3350 and 18 age- and sex-matched controls.
• Who: Children aged 6 to 12 being treated for constipation.
• How long: Samples before and every 30 minutes for 3 hours after a 17 g dose.
• Result: Ethylene glycol peaked at 1032.81 ng/mL (826.84-1486.13) at 90 minutes and triethylene glycol at 35.17 ng/mL (15.81-45.13); diethylene glycol did not change and was lower in the PEG group (40.13 vs 92.83 ng/mL, P = .008). A 17 g dose in 237 mL water contained ethylene glycol 1.32 +/- 0.23 micrograms/mL, against 0.07 micrograms/mL in the public water supply.
• Funding: not stated in the record fetched.

Daily PEG 3350 therapy in children was not associated with sustained elevation of EG, DEG, or TEG blood levels over levels in matched controls. Although EG and TEG levels increased after a standard dose of PEG 3350, their peak values remained well below toxic levels.

Where the evidence is mixed

Cochrane rated the certainty of its own primary-outcome evidence for childhood laxatives as low or very low. (Source 21)

• Systematic review, Very low certainty.
• Size: 25 randomised trials, 2,310 participants.
• Who: Children aged 0 to 18 with functional constipation.
• How long: Short follow-up.
• Result: GRADE downgraded for sparse data, inconsistency (heterogeneity) and high risk of bias; 14 of 25 studies at high risk of bias.
• Funding: not stated in the record fetched.

GRADE analyses indicated that the overall quality of the evidence for the primary outcome (number of stools per week) was low or very low due to sparse data, inconsistency (heterogeneity), and high risk of bias in the studies in the pooled analyses.

Where the research disagrees

Whether PEG should be preferred over lactulose for chronic constipation

• Lee-Robichaud and colleagues, Cochrane 2010, Meta-analysis of all ten randomised trials comparing the two: Polyethylene Glycol should be used in preference to Lactulose in the treatment of Chronic Constipation. (Source 17)
• Gordon and colleagues, Cochrane 2016, Meta-analysis of 25 randomised trials with GRADE assessment rating the primary outcome low or very low certainty: the results of the pooled analyses should be interpreted with caution because of quality and methodological concerns, as well as clinical heterogeneity, and short follow-up. (Source 21)

Whether trace ethylene glycol in PEG 3350 is a hazard to children

• Williams and colleagues (2018), Blood-level study in 9 treated children and 18 matched controls: Daily PEG 3350 therapy in children was not associated with sustained elevation of EG, DEG, or TEG blood levels over levels in matched controls. (Source 20)
• Williams and colleagues, on the single-dose finding that keeps the question open, Serial blood sampling over 3 hours after a 17 g dose: Although EG and TEG levels increased after a standard dose of PEG 3350, their peak values remained well below toxic levels. (Source 20)

How much

• Reference intake: There is no reference intake for a laxative; the dose is set by the product label or a prescriber. The over-the-counter label (MiraLAX, SPL effective 4 May 2026) directs adults and children 17 years and older to take one 17 g packet once a day dissolved in 4 to 8 ounces of any beverage. (Source 4)
• Upper limit: The over-the-counter label sets a duration limit rather than a dose ceiling: do not use more than 7 days, and anyone 16 or under should ask a doctor. The prescription bowel-preparation product is a single 4 litre course. (Source 4)
• Studied: The phase III adult trial started at 13.7 g/day dissolved in 125 mL of water and allowed titration up to 41.1 g/day. (Source 11)
• Studied: A paediatric dose-ranging trial compared 0.7 g/kg with 0.3 g/kg; the higher dose gave 1.30 more stools per week (95% CI 0.76 to 1.84). (Source 12)
• Studied: The Cochrane review of intractable childhood constipation included a trial using 0.5 g/kg/day PEG laxatives over 52 weeks. (Source 5)
• Studied: The bowel-cleansing product is a 4 litre solution containing 236 g of polyethylene glycol 3350 with added salts. (Source 22)

A common belief, and what the research shows

The belief: MiraLAX is antifreeze, it builds up in children, and it causes behavioural problems.

What the research shows: Polyethylene glycol 3350 is not ethylene glycol; it is a polymer that is 'absorbed in only trace amounts from the gastrointestinal tract'. The contamination question was measured directly in children: 'Daily PEG 3350 therapy in children was not associated with sustained elevation of EG, DEG, or TEG blood levels over levels in matched controls.' Ethylene glycol did rise for about 90 minutes after a dose, but 'their peak values remained well below toxic levels', and a 17 g dose contained less diethylene glycol than the local tap water used as a comparator. What the evidence does show is a different problem the slogan misses: real immediate allergy. The FDA adverse event database held '53 additional cases of possible PEG 3350 anaphylaxis.'

Questions and answers

What is it?

Polyethylene glycol 3350 is a synthetic polymer, sold as a white powder you dissolve in a drink. It is classed as an osmotic laxative and the gut absorbs it in only trace amounts. The over-the-counter version is 17 g of the pure polymer; the colonoscopy preparation is 236 g of the same polymer in a 4 litre jug with sodium sulfate, sodium bicarbonate, sodium chloride and potassium chloride added. (Source 18)

What does it do in the body?

It works by osmosis. The polymer holds water in the colon rather than letting it be reabsorbed, which produces a softer, wetter stool. The prescription bowel-preparation label describes the same mechanism as causing a diarrhoea that clears the bowel, usually within about four hours at the large dose. Because the polymer is poorly absorbed it does not act on the nervous system or the rest of the body. (Source 1)

Is it good or bad for you?

Good when the problem is hard, infrequent stool, and the amount matters. The over-the-counter label claims only that it relieves occasional constipation and generally produces a bowel movement in one to three days, and the trials support that. The bad side splits in two: mild and common (flatulence, abdominal pain, nausea, diarrhoea, headache; nausea and bloating in up to half of people taking the 4 litre preparation) and rare but serious (anaphylaxis, and with the bowel preparation, electrolyte disturbance, seizures, arrhythmias and ischaemic colitis). (Source 12)

How do you get more of it?

It is a manufactured product, so more means a larger or more frequent dose, which is a prescriber's decision beyond the label. The over-the-counter dose is one 17 g packet once a day in 4 to 8 ounces of any beverage. In trials, higher doses did produce more stools: 0.7 g/kg gave 1.30 more stools per week than 0.3 g/kg in children, and the adult phase III trial allowed titration from 13.7 g/day up to 41.1 g/day. (Source 12)

If it is harmful, what reduces it?

Because almost none of it is absorbed, stopping the powder is all that is needed; it leaves in the stool. The label's own triggers for stopping are symptomatic: under 'Stop use and ask a doctor if' it lists rectal bleeding or worsening pain, getting diarrhoea, and needing a laxative for longer than 1 week. If an allergic reaction is the problem, avoidance is the answer, and testing shows people allergic to PEG 3350 may also need to avoid polysorbate 80. (Source 10)

Why might someone be low in it or missing it?

Nobody is deficient in PEG 3350; it is a medicine, not a nutrient. The practical version of the question is why it might not work. The trials give two answers: the dose may be too low, since 0.3 g/kg worked less well than 0.7 g/kg in children, and the problem may not be simple functional constipation, which is why the label says to ask a doctor about nausea, vomiting, abdominal pain, a sudden change in bowel habit lasting over two weeks, or irritable bowel syndrome. (Source 12)

Which whole foods contain it or feed it?

No whole food contains polyethylene glycol 3350. It is a synthetic polymer, and in the bowel-preparation product it is supplied as a white powder with added sodium and potassium salts. PEG and the closely related polysorbates are, however, widely used as excipients in medicines and processed products, which is why people allergic to the laxative can react to things that look unrelated. The foods that matter for constipation itself (fibre, fluid) were tested against PEG in Cochrane and showed no significant difference in stools per week. (Source 22)

What happens if you do not have it?

Nothing happens from not having PEG itself; the question is what happens if constipation is untreated. In the placebo arms of the paediatric trials, children passed about 2.6 fewer stools a week than those on PEG, and in the adult trial the placebo group averaged 1.6 spontaneous bowel movements a week against 4.3 on PEG. Cochrane also found that children left on lactulose instead needed an additional laxative more often, 31 percent versus 18 percent. (Source 12)

How can you test for it?

There is no clinical test for PEG 3350 and none is needed, because it is barely absorbed. In research, glycol breakdown products can be measured in blood by mass spectrometry, which is how the contamination question was settled: ethylene, diethylene and triethylene glycol were measured in 9 treated children and 18 matched controls and showed no sustained elevation. For suspected PEG allergy there is a usable test: skin testing and graded provocation, with anti-PEG IgE and IgG assays available in research settings. (Source 9)

References

1. DailyMed, U.S. National Library of Medicine. PEG-3350 and Electrolytes for Oral Solution - FDA prescribing information, Section 12 CLINICAL PHARMACOLOGY (SPL effective 2026-07-24). 2026. Read the source
2. DailyMed, U.S. National Library of Medicine. MiraLAX (polyethylene glycol 3350) powder, for solution - OTC Drug Facts, Use section (Bayer HealthCare LLC, SPL effective 2026-05-04). 2026. Read the source
3. DailyMed, U.S. National Library of Medicine. PEG-3350 and Electrolytes for Oral Solution - FDA prescribing information, Section 1 INDICATIONS AND USAGE (SPL effective 2026-07-24). 2026. Read the source
4. DailyMed, U.S. National Library of Medicine. MiraLAX (polyethylene glycol 3350) powder, for solution - OTC Drug Facts, Directions (Packet Only) (Bayer HealthCare LLC, SPL effective 2026-05-04). 2026. Read the source
5. The Cochrane database of systematic reviews. Treatments for intractable constipation in childhood.. 2024. PMID 38895907, DOI 10.1002/14651858.CD014580.pub2. Read the source
6. DailyMed, U.S. National Library of Medicine. PEG-3350 and Electrolytes for Oral Solution - FDA prescribing information, Section 7 DRUG INTERACTIONS (SPL effective 2026-07-24). 2026. Read the source
7. DailyMed, U.S. National Library of Medicine. PEG-3350 and Electrolytes for Oral Solution - FDA prescribing information, Section 5.4 Renal Impairment (SPL effective 2026-07-24). 2026. Read the source
8. DailyMed, U.S. National Library of Medicine. PEG-3350 and Electrolytes for Oral Solution - FDA prescribing information, Section 5.3 Seizures (SPL effective 2026-07-24). 2026. Read the source
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