Wegovy ingredients: what the pen actually contains

The common misconception: Wegovy isn't simply 'a hormone injection'

A lot of people assume Wegovy works by flooding the body with a natural hormone, as if the pen contains something extracted directly from human tissue. That's not quite right. Semaglutide is a synthetic analogue of GLP-1 (glucagon-like peptide-1), a hormone your gut releases after eating. Researchers at Novo Nordisk modified the molecule significantly (attaching a fatty acid chain that extends its half-life from a few minutes to roughly a week) so that a single weekly injection can maintain meaningful blood levels throughout the dose interval.

This structural modification is why semaglutide is not identical to the GLP-1 your body produces, and why it has a distinct pharmacological profile. It binds to and activates GLP-1 receptors in the brain's appetite centres, in the gut (slowing gastric emptying), and in the pancreas (stimulating insulin release in response to glucose). The therapeutic effect comes from this sustained receptor activation, not from simply topping up a deficiency. That distinction matters when patients ask whether they are 'replacing' something their body should be making on its own. They are not, they are using a drug that mimics and amplifies a natural signal for longer than the body normally would.

You can read a plain-language summary of how semaglutide works, its licensed uses, and its known side-effect profile on the NHS medicines page for semaglutide.

What the ingredients list in Wegovy actually contains

Wegovy's Summary of Product Characteristics lists the formulation precisely. The active ingredient is semaglutide. The inactive ingredients (excipients) are: disodium phosphate dihydrate, propylene glycol, phenol, and water for injections.

Each of those excipients earns its place. Disodium phosphate dihydrate acts as a buffer, keeping the pH of the solution stable so the semaglutide molecule remains intact from manufacture through to the moment of injection. Propylene glycol is a solubiliser, it helps maintain the right physical properties of the liquid at refrigerated temperatures. Phenol serves as the antimicrobial preservative, preventing contamination across the multiple doses held within a single pen. Water for injections is the carrier medium, produced to pharmaceutical-grade standards.

There are no sugars, no animal-derived excipients, and no gluten-containing components in the listed formulation. Patients with specific ingredient sensitivities should always cross-reference the current Patient Information Leaflet, since excipient details can change between manufacturing batches or following a regulatory variation. The authoritative source is the product's entry on the electronic Medicines Compendium (eMC), which holds the up-to-date Wegovy SmPC.

It is also worth understanding that the inactive ingredients in Wegovy are not therapeutically inert from an allergy standpoint, if you have a known hypersensitivity to any of them, your prescriber needs to know before treatment starts.

How Wegovy's ingredients differ from those of similar medicines

Patients transferring from another GLP-1 medicine, or those comparing options, sometimes ask whether the ingredients overlap. Ozempic also contains semaglutide and shares broadly similar excipients, but it is licensed for type 2 diabetes management rather than weight loss, and the injection volumes and pen designs differ. Rybelsus is oral semaglutide for diabetes, its formulation is entirely different because it uses sodium N-[8-(2-hydroxybenzoyl)amino]caprylate (SNAC) as an absorption enhancer to survive the gut environment.

The newer Wegovy overview page covers how these licensing distinctions play out in practice. Tirzepatide (Mounjaro), by contrast, has a different active ingredient altogether (it activates both GLP-1 and GIP receptors) and its formulation list differs accordingly. If you are curious specifically about how semaglutide compares to tirzepatide at the molecular level, the page on whether Ozempic and Wegovy share the same ingredients covers the semaglutide side of that comparison in detail.

For anyone weighing up which treatment might suit their situation, a broader look at weight-loss treatment options sets the context, though the decision itself sits with a prescriber who can review your full medical history.

Practical considerations the ingredients list raises

Knowing the formulation has real practical implications, not just academic ones. Phenol, for instance, can degrade if the pen is left in direct sunlight or exposed to temperatures above 30°C for extended periods, which is part of why Wegovy requires refrigerated storage between 2°C and 8°C. Once in use, pens may be kept at room temperature for a period, but for the precise storage window you should follow the current Patient Information Leaflet rather than any third-party summary, since storage guidance is a detail the regulator can update.

There is one timing point worth flagging here: if you are planning to order treatment around a bank holiday, a payday delivery, or a period when you are travelling, storage conditions at home need a moment's thought before the pen arrives. A pen that has spent two days unrefrigerated in a courier depot is not equivalent to one that arrived correctly cold-chain handled.

The main ingredient in Wegovy page goes into more depth on semaglutide's mechanism for readers who want the pharmacology. Those with questions about how the formulation interacts with a specific health condition (including whether Wegovy can affect gout) will find dedicated pages covering those angles. Any concern specific to your own circumstances should be raised with a clinician who has your full picture.

If you are ready to explore whether Wegovy is clinically suitable for you, check your eligibility with our prescribers, consultations are free, reviewed the same day by a GPhC-registered clinician, not software.