What do you call the weight loss injection — and does the name matter?

What are the actual medical names for the weight loss injections?

There are two licensed options in the UK. The first is tirzepatide, sold under the brand name Mounjaro and made by Eli Lilly. It works by activating two gut-hormone receptors simultaneously (GIP and GLP-1) which suppresses appetite and slows how quickly food leaves the stomach. The second is semaglutide, sold under the brand name Wegovy and made by Novo Nordisk. Semaglutide acts on the GLP-1 receptor alone. Both are once-weekly subcutaneous injections delivered via pre-filled pens.

The drug name (tirzepatide, semaglutide) is the international non-proprietary name, the same molecule regardless of which country you're in. The brand name is what Lilly or Novo Nordisk registered with the regulator. Both names appear on the packaging. Knowing both helps when you're reading clinical trial results, checking a pharmacy's stock, or verifying that what you've been offered matches what was assessed in the trials. The NHS medicines page on tirzepatide uses the drug name throughout, which is a useful reference if packaging feels confusing.

Neither name tells you what dose you'll start on. Treatment for both medicines begins at a low starter dose to allow your system to adjust, then titrates upward under prescriber guidance. Your prescriber sets that schedule, it isn't something to self-manage.

Where do the nicknames like 'skinny jab' and 'weight loss pen' come from?

The colloquial terms spread quickly once GLP-1 medicines became high-profile in the UK press. 'Skinny jab' is probably the most common, it's worth naming it once here just to say plainly that it has no clinical meaning and, if anything, understates what these medicines are. They're treatments for obesity, a recognised medical condition, not cosmetic tools. The MHRA has been explicit that GLP-1 medicines are not assessed or approved for quick or cosmetic weight loss.

If you're trying to understand what the weight loss injection is actually called, the informal terms in circulation are a reasonable starting point but none of them tells you which medicine, which brand, or which licence is relevant to your situation. 'Weight loss pen' is a neater shorthand and broadly accurate as a description of the delivery device, but if you want to understand what the weight loss injections actually are, it's worth knowing that the term covers both Mounjaro and Wegovy, and the two medicines have different mechanisms, different trial evidence, and slightly different eligibility criteria. 'Obesity injection' is similarly broad. If you've seen a product advertised under a nickname rather than a proper drug or brand name, that's worth treating as a prompt to check it against the GPhC pharmacy register before going further.

One practical habit worth building: look up the pharmacy selling the product on the GPhC register, it takes under a minute, and a legitimate dispensing pharmacy will always appear there.

Is Ozempic the same as the weight loss injection?

This is one of the most common points of confusion. Ozempic contains semaglutide, the same active ingredient as Wegovy. But Ozempic is licensed in the UK for type 2 diabetes, not for weight management. The two products use different doses and were approved on the basis of different clinical evidence. Wegovy's 2.4mg weekly maintenance dose is higher than the doses studied in Ozempic's diabetes trials, and its licence is specifically for weight loss. If you want a clear breakdown of what the two weight loss injections are and how they differ, that sets out the distinction between tirzepatide and semaglutide directly.

Conflating the two matters because someone seeking Ozempic 'for weight loss' is looking for a medicine used outside its licensed indication, something that requires careful clinical justification and isn't straightforward to prescribe legally for that purpose. A number of press stories about celebrities or shortages involved Ozempic, not Wegovy. The NICE technology appraisal for semaglutide in weight management (TA875) refers specifically to Wegovy, not Ozempic.

Similarly, Rybelsus is oral semaglutide but licensed for type 2 diabetes, not to be confused with the Wegovy tablet (oral semaglutide for weight management, approved by the MHRA in June 2026). Same molecule, different licence, different product. Names here really do carry clinical weight. A full overview of all three weight loss injection options sets this out clearly, and if you'd like a broader picture, our page covering all the weight loss injections available brings together the complete range in one place.

Does it matter which name you use when talking to a prescriber or pharmacist?

Practically speaking, most prescribers will understand what you mean if you say 'the weight loss injection', but using the correct name gets you a more useful conversation faster. If you say 'tirzepatide' or 'Mounjaro', a prescriber knows immediately which mechanism, which dose range, and which eligibility criteria apply. If you say 'the skinny jab', there's a clarification step first.

It also matters when you're comparing costs. Prices are quoted per pen, per medicine, by dose, and the cost structure of Mounjaro differs from Wegovy. Understanding that these are separate products with separate price points is part of making a properly informed decision. For context on how pricing works for private weight loss treatment, the treatment overview sets out what's included at each stage. Our clinical team reviews every consultation individually, regardless of which medicine you're enquiring about.

If you're still working out which option might suit your situation, our weight loss injection page covers both medicines side by side. And if you have a specific question that isn't answered there, the FAQs are a reasonable next stop before starting a formal consultation.