What are the weight loss injections called — and what makes them different?

The biggest myth: there is one "weight loss jab" (in fact there are two distinct medicines

Most people searching for what the weight loss injection is called have seen a single phrase) "the jab", "the slimming injection", occasionally "the skinny jab", as though one product dominates. The reality is more nuanced. Two separate medicines are licensed for weight management in UK adults: Mounjaro and Wegovy. They share a family resemblance (both mimic gut hormones, both slow gastric emptying, both reduce appetite) but they are pharmacologically different, manufactured by different companies, and carry different clinical profiles.

Mounjaro is made by Eli Lilly. Its active ingredient, tirzepatide, activates both the GIP receptor and the GLP-1 receptor simultaneously, it is the only dual-agonist weight management medicine licensed in the UK. Wegovy is made by Novo Nordisk. Its active ingredient, semaglutide, targets the GLP-1 receptor only. That single structural difference translates into real-world distinctions in average weight loss seen in clinical trials, in side-effect nuance, and in who a prescriber might favour for a given patient. If you want to read about all the weight loss injections available in the UK, the comparison is worth making carefully rather than treating them as interchangeable.

One further clarification matters: Ozempic is also semaglutide, but it holds a licence for type 2 diabetes management, not weight loss. The MHRA is clear on this distinction. Presenting Ozempic as a weight loss medicine would be legally and clinically inaccurate.

What the trial evidence actually says about results

When people ask what the new weight loss injection is called, they often really want to know which one works better. The short answer is that both produce meaningful results; the longer answer involves specific numbers from specific trials, and those numbers carry conditions.

In SURMOUNT-1, a 72-week randomised trial involving 2,539 adults with obesity and no diabetes, tirzepatide at the highest dose produced an average body-weight reduction of around 20–21%. The trial was published in the New England Journal of Medicine and formed the cornerstone of NICE's recommendation of tirzepatide (TA1026). In STEP 1, a 68-week trial of semaglutide 2.4mg, participants lost around 15% of body weight on average. A more recent head-to-head study, SURMOUNT-5, found tirzepatide produced greater average weight reduction than semaglutide 2.4mg over 72 weeks in adults with obesity.

These are population averages from controlled trial conditions. Individual results vary, and a prescriber reviewing your full picture (health history, current medicines, lifestyle) is the right person to set realistic expectations. Results also depend on following the dose escalation schedule and making the dietary and activity changes that both medicines are licensed alongside, not instead of.

For context on how costs compare across the two options, our overview of weight loss injection pricing sets out what a legitimate private prescription typically includes and what to watch for when prices seem unusually low.

Who can actually be prescribed these medicines

Both Mounjaro and Wegovy are licensed for adults with a BMI of 30 or above, or 27 or above where at least one weight-related health condition is present, for example, high blood pressure, raised cholesterol, obstructive sleep apnoea, prediabetes or type 2 diabetes. Lower BMI thresholds apply for some ethnic backgrounds under UK clinical guidance. BMI alone does not determine prescribing; a prescriber weighs the full clinical picture, including any medicines you already take and any contraindications in your health history.

Neither medicine is recommended during pregnancy, breastfeeding or when actively trying to conceive. They are not licensed for anyone under 18. People with a personal or family history of medullary thyroid carcinoma or MEN2 syndrome should not use tirzepatide; other conditions require careful prescriber review before starting either medicine.

On the NHS, access follows a phased rollout tied to NICE guidance, criteria are strict and waiting lists exist. Private prescribing through a regulated pharmacy is the alternative for people who do not meet NHS thresholds or prefer not to wait. If you are curious about accessing weight loss injections in specific parts of the UK, availability and waiting times vary by area. A more complete look at the three weight management medicines commonly discussed in the UK also covers orlistat, the oral option that works through a different mechanism entirely.

Checking the pharmacy before you order

Because these are prescription-only medicines, the route you take to get them matters as much as which one you choose. If you have been wondering what the newest weight loss injection is called, it is worth knowing that the MHRA has warned repeatedly about counterfeit weight loss pens sold online and via social media, fake pens have been found to contain insulin rather than the medicine on the label, with serious consequences for some buyers. Ordering from a seller that does not require a prescription is a significant safety risk, not a shortcut.

Any legitimate online pharmacy dispensing Mounjaro or Wegovy must be registered with the General Pharmaceutical Council. You can verify any pharmacy's registration at the GPhC pharmacy register, it takes about thirty seconds and is the single most reliable check available to you. At nume, every consultation is personally reviewed by a GPhC-registered Independent Prescriber on the day it is submitted. Your pen arrives via DPD the next working day, in plain packaging, with no subscription attached. If you place your order before noon, it can leave our pharmacy the same day once your prescriber has approved it, useful if you are trying to fit an order in before the school run.

If you are ready to talk to a prescriber about whether Mounjaro or Wegovy suits your situation, our free consultation is the place to start. Our clinical team is here to answer questions, not just process forms.