Macrogol (polyethylene glycol laxative)
PEG 3350, PEG 4000, MiraLAX, Movicol, Forlax, Transipeg, Laxido, Fortrans
Forms: Powders for solution, plain or with added salts (electrolytes); much larger bowel-cleansing preparations are used before colonoscopy.
An osmotic laxative: a large molecule that keeps water in the bowel and softens stools. Sold without prescription; a constipation guideline gives it a strong recommendation.
Legal status: Sold without prescription in most countries (rules vary by country); not on the WADA Prohibited List.
What it gives
What people use it for and what the sources report. Strength is a general category from the literature: mild, clear or strong.
Purpose
Used for constipation, including on GLP-1 drugs, where constipation can last longer than other gut side effects and a consensus advises stool softeners. Unlike magnesium laxatives it adds no magnesium load. Medical use: occasional and chronic constipation.
What people seek and what studies show
In adults with chronic constipation, trials showed more complete bowel movements than placebo, with a durable response (AGA-ACG 2023: strong recommendation, moderate certainty of evidence). Not studied in athletes or PED users; it has no effect on training or body composition.
Effects
Evidence: Approved medicine — studied in people for its medical use
Possible side effects
Possible does not mean certain: whether they appear depends on dose, duration, individual response and monitoring. Below — what to watch for and how to notice it early.
2 possible side effects
level · how often it is reportedWhat the levels mean
Level: general category from the literature, not your personal risk
How often
- common
- reported often
- possible
- reported in some people
- rare
- reported occasionally
How to lower the risks
For 2 of 2 possible side effects there are specific ways to lower the chance: everyday measures, supplements and options a doctor may consider. No measure removes a risk completely.
Low-level side effects
How each option helps (13)
- Avoiding alcohol and other liver stressors — Alcohol irritates the stomach, adds to aspirin-related stomach bleeding and is a main cause of pancreatitis; avoiding it lowers that part of the risk, not drug nausea.
- Fluid & electrolyte management — Dehydration makes gut complaints in long or hot sessions more likely; drinking enough helps that part, not nausea from drugs or pancreatitis.
- Working with a doctor — Assesses persistent vomiting or severe belly pain (possible pancreatitis or gallstones), can add stomach protection to aspirin and adjusts GLP-1 treatment when nausea persists.
- Omeprazole and other proton-pump inhibitors (PPIs) — A doctor may consider it for heartburn, reflux, dyspepsia or ulcer cover with aspirin or NSAIDs (label, guidelines). It does little for nausea or diarrhea; long-term use has its own risks.
- Famotidine (H2 blockers) — Relieves and prevents occasional heartburn (label); it does not help nausea or diarrhea. For reflux damage or long-term ulcer cover a doctor usually turns to a PPI.
- Loperamide — Eases acute diarrhea, including on GLP-1 drugs (consensus), but not its cause; not for nausea or bloody stools. Fluids and salts still come first.
- Magnesium carbonate — An antacid for heartburn and indigestion (label), often combined with other antacids; it does not help nausea and may itself loosen stools. Not with weak kidneys.
- Magnesium citrate — In larger amounts a saline laxative for occasional constipation (label); not for nausea. It causes cramps and loose stools itself; ask a doctor first with kidney disease.
- Magnesium hydroxide — Labeled as an antacid for heartburn and a laxative for occasional constipation; short-term relief only, not for nausea. It can itself cause diarrhea; not with weak kidneys.
- Magnesium oxide — An osmotic laxative that eases constipation (conditional guideline advice); not for nausea or heartburn. It loosens stools itself; with weak kidneys blood magnesium can rise.
- Pancreatin + dimeticone (Pankreoflat) — Registered for heaviness and bloating after meals; it does not ease drug nausea, heartburn or aspirin stomach pain. Not with pork or cow's milk protein allergy or acute pancreatitis.
- Probiotics — May ease diarrhea, for example on GLP-1 drugs (consensus); in sport studies they mostly did not reduce exercise gut symptoms. Not for nausea or heartburn.
- Psyllium husk fiber — Soluble fiber eases constipation, including on GLP-1 drugs, and can firm loose stools; it does not help nausea or heartburn and can itself cause bloating and gas.
How each option helps (18)
- Fluid & electrolyte management — Weighing before and after training shows sweat loss; ACSM advises keeping it under about 2% of body weight. Salty fluids help, but they do not offset the losses diuretics cause.
- Heat acclimatisation & cooling — Fluid and salt balance improves, but acclimatised athletes sweat more, so fluid needs go up, not down; it does not replace drinking or offset diuretic losses.
- Regular blood tests — Sodium, potassium, magnesium and kidney tests catch dangerous shifts from diuretics, clenbuterol or thyroid hormone; they do not make those drugs safe.
- Electrolytes (sodium, potassium, magnesium) — Replacing sweat sodium and fluid may lower the chance of dehydration and heat cramps; it does not remove heat-illness risk or make diuretics or water cuts safe, and its potassium is risky with ARBs.
- Magnesium — Replaces magnesium lost in sweat or with diuretics; there is no good evidence that it stops exercise cramps. It does not make diuretic use or extreme weight cutting safe.
- Magnesium aspartate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium carbonate — Supplies magnesium, but it is used mainly as an antacid and there are few data on it as a supplement; chalk on the hands supplies none. Does not make diuretics safe.
- Magnesium chloride — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium citrate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium gluconate — Replaces magnesium lost in heavy sweat or with diuretics. Cochrane found no trials in exercise cramps; runners who cramped did not have lower blood magnesium. Does not make diuretics safe.
- Magnesium glycinate (bisglycinate) — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium lactate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium malate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium orotate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Magnesium oxide — Supplies some magnesium, but far less is absorbed than from soluble salts; Cochrane found no trials in exercise cramps. Does not make diuretics safe.
- Magnesium taurate — Replaces magnesium lost in heavy sweat or with diuretics. A Cochrane review found no trials of magnesium for exercise-associated cramps. Does not make diuretics safe.
- Potassium — Replaces potassium lost with sweat or thiazide and loop diuretics when a test shows it is low; it does not make diuretics safe and is risky with potassium-sparing ones.
- Taurine — Used in practice against cramps on clenbuterol or diuretics; trials show fewer cramps only in liver disease, the clenbuterol link is rat data. Such cramps can mean low potassium: get a blood test.
Check-ups and blood tests
Which tests and check-ups to do and when. This is a guide — agree the exact schedule with a sports physician.
Myth & fact
“A laxative used regularly soon stops working.”
For polyethylene glycol, trials in chronic constipation showed a durable response (AGA-ACG guideline). Constipation that is new, severe or comes with bleeding still needs a doctor.
Combinations
No specific combination notes for this substance yet. The stack check still adds up side effects that several substances share.
Sources
Possible side effects by body system, combinations, how to lower the risks and which tests to do — free.
Open the stack check