Wegovy or Mounjaro: working out which injection suits you

Step 1: understand what each medicine actually does inside your body

Wegovy works through a single pathway. Semaglutide mimics GLP-1, a gut hormone released after eating that signals fullness to the brain, slows how quickly the stomach empties, and reduces appetite. It is given as a once-weekly subcutaneous injection, starting at 0.25mg and titrated up over several months to a standard maintenance dose of 2.4mg, and, since January 2026, a higher 7.2mg dose is also licensed for adults with a BMI of 30 or above. You can read the full NHS patient information on semaglutide for a plain-English breakdown of the mechanism and what to expect.

Mounjaro takes a different approach. Tirzepatide activates two receptors simultaneously: GLP-1 and GIP (glucose-dependent insulinotropic polypeptide). GIP is thought to amplify the appetite-reducing and metabolic effects beyond what GLP-1 alone achieves. The result, in trials, is a somewhat larger average reduction in body weight. Treatment begins at 2.5mg (a dose whose job is to let your system adjust, not to produce the bulk of any weight change) and rises in steps up to 15mg. It is the only medicine of its kind licensed for weight management in the UK.

This mechanistic difference matters clinically: it is one reason the trial results differ, and one reason a prescriber will look at your individual response rather than simply handing you the medicine that performed better on average in a study.

Step 2: look at what the evidence actually says, and where its limits lie

A question our prescribers hear most weeks is whether the trial results translate directly into a personal prediction. They don't, and being honest about that is important.

In the STEP 1 trial (68 weeks, semaglutide 2.4mg), participants lost around 15% of body weight on average. The SURMOUNT-1 trial for tirzepatide (72 weeks, up to 15mg) recorded average reductions of around 20–21% at the highest dose. SURMOUNT-5 then put the two medicines head-to-head directly (751 adults with obesity, no diabetes, 72 weeks) and tirzepatide again produced greater average weight loss. The NICE appraisal of tirzepatide references these results and discusses why indirect comparisons consistently favour tirzepatide. That said, the 7.2mg Wegovy dose, approved by the MHRA in early 2026, showed around 20.7% average loss over 72 weeks in trials, which narrows the gap considerably at the top of the semaglutide dose range.

Averages describe populations, not individuals. Some people respond more strongly to semaglutide; others plateau on one medicine and do better when switched. The right reading of this evidence is not "Mounjaro wins" but "on average, tirzepatide produced more weight loss in trials, and both produced clinically meaningful results." Your prescriber weighs this alongside everything else.

For a fuller look at how these two medicines compare across side effects, eligibility and cost, the detailed Wegovy assessment page works through the nuances.

Step 3: factor in eligibility, practical considerations and your existing medications

Both medicines share a similar eligibility threshold: adults with a BMI of 30 or above, or 27 or above with at least one weight-related condition such as high blood pressure, type 2 diabetes, obstructive sleep apnoea or high cholesterol. Lower BMI thresholds apply for some ethnic backgrounds under UK guidance. That rough overlap means eligibility alone rarely settles the Wegovy-or-Mounjaro question.

Practical differences can matter more. If needles are a concern, Wegovy's 7.2mg pen is a single auto-dosing injection with a covered needle that locks after use, a design detail some patients find less daunting. Injection site guidance covers the abdomen, thigh and upper arm options that apply to both medicines. Storage is similar for both: refrigerated until use, with a limited room-temperature window that varies by product, the Patient Information Leaflet for each medicine gives the exact figures, and relying on those rather than secondary sources is the safest habit.

Oral contraceptive users should note that tirzepatide slows gastric emptying enough to reduce pill absorption in the first four weeks of treatment and after each dose increase; adding a non-oral contraceptive method during those windows is recommended. NHS England's guidance on weight-management injections covers this clearly. The same absorption concern does not have the same documented evidence base for semaglutide, though your prescriber will review all your medications regardless of which medicine is under discussion.

If you want to understand the cost dimension before booking a consultation, the Wegovy cost page sets out what private treatment typically involves and what a transparent price should include.

Step 4: how a prescriber reaches the decision, and what comes next

After the steps above, many people still feel uncertain, and that is exactly where a prescriber's judgment comes in. At nume, every consultation is read by a GPhC-registered Independent Prescriber, a real clinician who reviews your health history, current medications, BMI, weight-related conditions and any contraindications. Software does not make that call.

If you are already on one of these medicines and wondering whether to switch, that too is a conversation for your prescriber. Transfer patients are assessed on the basis of their current treatment and any evidence of how they are responding. The Wegovy treatment overview and the semaglutide information page give further background on how Wegovy works in practice, while the treatment options overview covers the broader landscape of weight-loss medicines licensed in the UK.

The starting point, whether you lean towards Wegovy or Mounjaro, is a free consultation. Our clinical team reviews every case individually, and there is no obligation after the assessment. If you have questions before you begin, the FAQs page covers the most common ones.