B12 and Wegovy: does semaglutide affect your vitamin B12 levels?

Where does the "B12 and Wegovy" idea actually come from?

A question our prescribers hear most weeks runs something like: "I've seen clinics offering semaglutide mixed with B12, should I be getting that instead?" The answer requires unpicking two quite different things.

In some countries, and on a number of UK-facing social media accounts, compounding pharmacies have marketed injectable mixtures described as "semaglutide with B12". These are not Wegovy. They are unlicensed compounded preparations that have not been assessed for quality, sterility or efficacy by the MHRA. The MHRA has warned explicitly about unsafe products sold online, and the Yellow Card scheme allows anyone to report a suspect seller. Buying a compounded semaglutide product without a valid UK prescription from a GPhC-registered pharmacy is not a safe route to weight management treatment.

Wegovy itself is a precisely manufactured, single-ingredient weekly injection produced by Novo Nordisk to pharmaceutical-grade standards. It does not contain B12. The two topics intersect not because they belong together as a treatment, but because people researching semaglutide online encounter both terms and reasonably want to know if there is a clinical connection. There is, but it is a nutrition question, not a product question. If you want to understand more about how B12 and semaglutide relate to one another, that dedicated page covers the topic in detail, and you can also read more about how semaglutide works as a weight management medicine on the semaglutide overview page.

Could Wegovy affect your B12 levels?

Semaglutide is a GLP-1 receptor agonist. One of its key mechanisms is slowing the rate at which the stomach empties its contents into the small intestine, which is a large part of why appetite falls on treatment. That same slowing has led researchers to ask whether long-term use might affect the absorption of nutrients that rely on gastric processes, B12 among them.

Vitamin B12 absorption is a multi-step process. Stomach acid and a protein called intrinsic factor are needed to release and then bind dietary B12 before it can be absorbed in the small intestine. Anything that meaningfully alters gastric function can, in theory, reduce how efficiently this happens. Metformin (another medicine used in weight management and type 2 diabetes) has a well-documented association with B12 depletion over time, and some clinicians have wondered whether GLP-1 medicines might carry a similar signal.

The honest answer is that robust, long-term data specific to Wegovy and B12 in weight-management populations is still limited. Our page on semaglutide and vitamin B12 goes into more depth on what the current evidence does and does not show. The NHS medicines guidance for semaglutide does not list B12 deficiency among the recognised side effects of Wegovy. If you eat a varied diet including meat, fish, eggs or dairy, your B12 status is unlikely to be dramatically altered by Wegovy alone. The risk is more plausible in people who already have borderline B12 levels, follow a strict vegan diet, or take other medicines that affect B12 absorption. A routine blood test through your GP is the sensible way to check.

What should you actually do if you're worried about B12 on Wegovy?

First, speak to your prescriber rather than self-supplementing. B12 injections (the kind a GP prescribes for a diagnosed deficiency) are a different matter from the B12 added to compounded semaglutide vials sold online, and conflating the two is how people end up buying unlicensed products they did not need.

If blood tests show your B12 is low or low-normal, your GP can advise on supplementation, whether oral B12 tablets or, where absorption is genuinely impaired, prescribed injections. Over-the-counter oral B12 supplements are widely available and safe for most adults at standard doses. The decision should follow a test result, not a marketing claim.

On diet more broadly: people on Wegovy eat less, and eating less means the margin for nutritional adequacy narrows. Prioritising protein, vegetables and a varied diet matters more on treatment than it does off it. If you have come across compounded mixtures and are curious about what colour semaglutide with B12 is, that page explains the visual differences and why they matter when assessing what you have been sent. This is one of the reasons that good weight management support (the kind that includes dietary guidance alongside the prescription) makes a practical difference. The Wegovy treatment page covers what clinical support looks like through a regulated UK service.

For those comparing costs of private weight management treatment, the Wegovy price comparison page sets out what a legitimate private prescription in the UK typically includes, which is worth reading before committing to any provider.

At nume, every consultation is reviewed personally by a GPhC-registered Independent Prescriber. If B12 or other nutritional concerns are relevant to your health picture, that is exactly the kind of thing a prescriber can take into account. You can also browse the weight loss treatment options page to understand the broader landscape before starting.

If you have further questions, our FAQs cover many common queries, or you can reach us directly via the contact page. When you are ready to take the next step, start your free consultation and a prescriber will review your circumstances the same day.