What semaglutide is mixed with — and why it matters

What the licensed Wegovy injection actually contains

The Wegovy pre-filled pen is a clear, colourless aqueous solution. Its active ingredient is semaglutide at the dose your prescriber has authorised. The inactive ingredients are disodium phosphate dihydrate, propylene glycol, phenol, and water for injections. That is the complete list. There is no B12, no peptide blend, no lipotropic agent. Novo Nordisk manufactures it to pharmaceutical-grade standards under MHRA oversight, and every batch entering the licensed UK supply chain has been subject to that regulatory scrutiny.

The oral Wegovy tablet (approved by the MHRA in June 2026 as the first oral GLP-1 medicine licensed for weight management in the UK) adds one more ingredient worth understanding: SNAC. Sodium N-[8-(2-hydroxybenzoyl)amino]caprylate is an absorption enhancer rather than an active drug. Oral semaglutide is poorly absorbed on its own because stomach acid degrades it; SNAC transiently increases the local pH near the stomach lining and opens a pathway for the molecule to cross. You take the tablet on an empty stomach, with a small amount of plain water, and wait at least 30 minutes before anything else passes your lips, that sequence exists specifically so SNAC can do its job undisturbed. The NHS medicines guidance for semaglutide covers what each formulation contains if you want to read the detail directly.

Understanding the full semaglutide profile makes it easier to assess what you are being offered, licensed or otherwise.

Compounded semaglutide and the B12 question

Search online long enough and you will find semaglutide products advertised with additions: vitamin B12, cyanocobalamin, NAD+, or various other compounds. Some of these are sold by clinics or overseas pharmacies as bespoke mixes. It is worth being direct about what that means in the UK.

The MHRA licences medicines for specific formulations, specific doses, and specific manufacturing conditions. A compounded product that adds B12 or anything else to semaglutide is not that licensed product. It has not undergone the same stability testing, the same sterility verification, or the same efficacy review. The MHRA has warned publicly about fake and unlicensed weight-loss pens sold online (some counterfeit products seized in the UK have contained entirely different substances) and the rationale for using a GPhC-registered pharmacy connected to the authorised supply chain is precisely this. If you have seen references to a semaglutide and B12 combination, that product does not correspond to anything licensed in the UK for weight management.

A query our prescribers field regularly is whether adding B12 improves results or reduces side effects. There is no published clinical evidence from MHRA-reviewed trials that supports either claim for compounded versions. The legitimate answer to a B12 concern is a conversation with your GP or prescriber about your nutritional status independently of your semaglutide prescription.

What semaglutide interacts with in your body, the clinical mixing question

There is a second, equally legitimate reading of this question: what does semaglutide interact with once you take it? This is a clinical drug-interaction question, and it is the one your prescriber must assess before and during treatment.

Because semaglutide slows gastric emptying, it can alter how quickly other oral medicines are absorbed. Drugs with a narrow therapeutic window (certain antibiotics, anticoagulants, thyroid medications) may behave slightly differently in terms of timing. Oral contraceptives are a notable practical example: for women taking semaglutide, the absorption timing of the pill may shift, and NHS guidance recommends discussing contraception before starting treatment. There is a detailed look at medicines that require extra care alongside semaglutide on a dedicated page.

The interaction question is also why the free consultation at a service like nume is a clinical process rather than a formality. A prescriber reviews your current medicines, your medical history, and any relevant supplements before authorising treatment, the kind of review that cannot happen if a product is sold without a prescription. For a thorough picture of how Wegovy works as a treatment, the Wegovy overview covers the mechanism, the evidence, and the licensed indications.

If you are considering your options and want to understand the cost and access side of things, the weight-loss treatments page sets out what a private prescription through a regulated pharmacy actually includes.

Putting it together: the practical decision

When someone asks what semaglutide is mixed with, they are usually trying to answer one of three things: is what I've been offered legitimate; should I be concerned about a specific additive; or does semaglutide interact with something I already take. Each question has a clear answer.

The licensed product contains only what the SmPC lists. Anything described as semaglutide plus an additive is not that product and is not licensed in the UK. Drug interactions are real and individually assessed, which is why a prescriber, not a checkout page, makes the final call.

The range of semaglutide medicines available in the UK is broader than most people realise, spanning injection and tablet forms for weight management and separate products licensed for type 2 diabetes. Knowing which is which, and whether what you are looking at is genuinely licensed, is the starting point for any safe treatment decision.

You can also browse answers to common questions about starting treatment, or read about how our clinical team approaches prescribing on our clinical team page. When you are ready to check your eligibility, you can speak to our prescribers through a free consultation, reviewed the same day by a real clinician.