Semaglutide's CAS number and what it means for the medicine you're taking

What exactly is a CAS number, and why does semaglutide have one?

The Chemical Abstracts Service assigns a unique registry number to every distinct chemical substance ever documented in scientific literature. Semaglutide's number, 910463-68-2, was registered when the compound was first characterised and published. It has nothing to do with brand names or clinical approvals, it is simply a permanent address in the global chemical registry.

That permanence is useful. Regulatory agencies, including the MHRA here in the UK and the European Medicines Agency, use CAS numbers in dossiers to confirm they are evaluating the correct compound. Pharmacopoeial monographs reference them. When a manufacturer submits a Marketing Authorisation for a new semaglutide product, the CAS number anchors the chemical identity section of the submission, giving reviewers a fixed point of reference across thousands of pages of data.

For most people using Wegovy this is background information, but it becomes relevant when you are reading a clinical trial paper, a prescribing reference like the BNF entry for semaglutide, or a media story about a new formulation and you want to be certain the substance discussed is the one you are familiar with.

Is the molecule inside a Wegovy pen chemically identical to other semaglutide products?

Yes. The active molecule in Wegovy, in Ozempic, and in the Wegovy tablet shares CAS number 910463-68-2. One misconception that surfaces occasionally is the idea that the injectable and oral versions must be different drugs because the doses look so different, 2.4 mg by injection versus 25 mg by tablet at maintenance. The doses differ because oral bioavailability of large peptides is very low; the absorption enhancer (SNAC) in the tablet helps, but the body still absorbs only a fraction of the dose. More of the molecule is needed to achieve comparable blood levels. The molecule itself, though, is the same.

Brand names distinguish licensed indications, not chemical identities. Wegovy is licensed for weight management. Ozempic and Rybelsus carry a type 2 diabetes licence in the UK, the MHRA has been clear that these are not interchangeable for weight-loss purposes, regardless of shared chemistry. If you are curious about how this plays out for the newer tablet form, the page on oral semaglutide doses covers the escalation schedule in detail.

A practical note: anyone verifying the identity of a product they have received (for example, checking a Wegovy batch) should use the batch-verification route rather than the CAS number alone, since the CAS number cannot confirm that a pen contains genuine product at the right concentration. The Wegovy batch-checking guide explains how to do that properly.

Does the CAS number help identify counterfeit or diverted semaglutide?

Not directly. A CAS number identifies a compound by its chemical structure, but it cannot tell you whether a product has been manufactured under proper pharmaceutical-grade conditions, stored correctly, or filled to the claimed concentration. Counterfeit pens have historically contained a substance that might technically share a CAS number with a legitimate product while being produced in unlicensed conditions with no quality assurance, or, in some cases, an entirely different substance altogether.

The MHRA is the right authority here. Its Yellow Card reporting service allows anyone who suspects they have received a fake or substandard medicine to file a report, and it also accepts reports of adverse effects from legitimate products. The MHRA has issued repeated public warnings since 2023 about fake weight-loss pens sold through social media and unregistered websites, large seizures of counterfeit product have been made, and some fake pens were found to contain dangerous substances.

The only reliable protection is sourcing semaglutide through a pharmacy registered with the General Pharmaceutical Council. You can check any pharmacy against the GPhC register at any time. For further context on how the supply chain works and what safe private access looks like, the Wegovy treatment page is a good starting point, and the weight-loss treatments overview lays out the broader landscape of licensed options.

How does understanding semaglutide's chemistry fit into an informed clinical conversation?

Knowing that semaglutide is a GLP-1 receptor agonist (a synthetic peptide mimicking the gut hormone GLP-1, modified with a fatty-acid side chain to slow its breakdown) helps explain several things that patients often ask about. The side-chain modification is why it works for a full week from a single injection, rather than the hours a natural GLP-1 would last. It also helps explain why gastrointestinal effects are the most common early experience: the GLP-1 receptor is found throughout the gut, and activating it slows gastric emptying noticeably, particularly in the first weeks of treatment or after a dose increase.

These are the kinds of questions our prescribers discuss with patients most weeks, and having some background before that conversation tends to make it more useful. If you are considering semaglutide for weight management and want to understand whether it might be suitable for you, a free consultation is the natural next step, a prescriber reviews your health information on the same day, and no clinical decision is ever automated. You can start your free consultation whenever you are ready. For a broader comparison of the options, including how semaglutide and tirzepatide differ, the semaglutide and MCAS page and the cost context page may also be useful reading beforehand.