Polyethylene Glycol (PEG) in Medications
Polyethylene glycol, also called PEG or macrogol, is a widely used inactive ingredient found in laxatives, tablet and capsule coatings, and some injectable products. PEG hypersensitivity is uncommon but recognized clinically, and PEG drew broader attention as an excipient in the mRNA COVID-19 vaccines.
What is polyethylene glycol (PEG)?
PEG is a synthetic polymer used as a pharmaceutical excipient, meaning it is part of the formulation rather than the active drug. It is also called macrogol on many international labels, and it appears in a range of molecular weights, from low-weight liquids used as solvents to higher-weight grades used in coatings.
Like other inactive ingredients, PEG is selected for a functional purpose: it can act as a solvent, a bulking agent in osmotic laxatives, a film former in tablet coatings, or a stabilizing component in some parenteral and biologic products. As Reker et al. documented in Science Translational Medicine (2019), ingredients labeled inactive are not inert for every patient and can occasionally drive clinically meaningful reactions.
Which kinds of medications contain PEG?
PEG appears across several product categories rather than in a single drug class. Common categories include osmotic laxatives and bowel preparations, oral solid coatings, and a subset of injectable and biologic products that use PEG or PEGylated components.
Laxatives and bowel preparations
Higher-molecular-weight PEG is used as the osmotic agent in many laxative and colonoscopy preparation products, where it works by retaining water in the bowel.
Tablet and capsule coatings
PEG is used as a plasticizer and film-forming component in coatings for oral solid dosage forms, so it can be present in a tablet even when it is not the focus of the formulation.
Injectables and biologics
Some injectable and biologic products contain PEG or PEGylated components. PEG is an excipient in the mRNA COVID-19 vaccines (per the CDC), the example that brought the most public attention to this category.
Topicals and other dosage forms
PEG also serves as a base or solvent in some topical and other formulations. Because it spans dosage forms, the only reliable way to know is to check the specific product.
Because PEG is not limited to one category, identifying the specific products that contain it for a given patient requires checking that product's excipient list rather than relying on the drug class.
How does PEG hypersensitivity present?
PEG hypersensitivity is uncommon but recognized in the clinical literature, and reported reactions range from cutaneous symptoms to immediate, potentially severe reactions including anaphylaxis. Bruusgaard-Mouritsen et al. (2021) describe PEG allergy as an underrecognized cause of immediate-type hypersensitivity, in part because PEG is so widely distributed across products that the trigger can be missed.
Molecular weight can be clinically relevant in PEG hypersensitivity, and cross-reactivity with related compounds has been described. Where a reaction is suspected, the specific PEG grade and molecular weight in the product may matter, not just the presence of PEG.
Suspected PEG hypersensitivity is an allergy evaluation question for the patient's care team. This page is a reference on the excipient itself; it does not diagnose individual patients or confirm which products are safe for a specific person.
What should you verify with the manufacturer?
For a patient with known or suspected PEG hypersensitivity, confirm with the manufacturer whether the specific product contains PEG or macrogol and, where clinically relevant, the molecular weight of the PEG grade used. Published labeling does not always make the grade explicit.
- Presence of PEG or macrogol: confirm whether the excipient is present in the exact product and dosage form being dispensed.
- Molecular weight or grade: when a reaction history makes molecular weight relevant, ask which PEG grade is used.
- PEGylated components: for injectables and biologics, confirm whether PEGylated ingredients are part of the formulation.
- Sourcing or formulation changes: if a patient reports a new reaction to a previously tolerated product, confirm whether the formulation has changed.
Related excipient explainers
Plain-language references on the excipients clinicians ask about most. Each covers where the ingredient appears, who it affects, and what to verify with the manufacturer.
Gluten in medicationsHow gluten enters medications through starch-based excipients, and why a generic "starch" label does not reveal the botanical source.Lactose in medicationsWhere lactose appears as a filler and inhaler carrier, who needs to avoid it, and how to verify a specific product.Alpha-gal and medicationsWhich mammalian-derived excipients matter for alpha-gal syndrome, and what to confirm with the manufacturer.Magnesium stearateWhy this common lubricant can be animal or vegetable derived, and what that means for vegan, halal, kosher, and alpha-gal needs.
Back to the education hubNeed to know whether a specific medication contains PEG?
This page covers PEG in general. To check the excipient profile of a specific product against a patient's exclusions, screen it in the AllergenMaps tool.