Mounjaro®
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Start journey Learn moreWhy Wegovy can feel less effective when you've already been on Mounjaro
You moved from a dual-receptor medicine to a single one — here's why that matters
Picture a Monday morning: Mounjaro pen in the fridge door, injection done, and within weeks your appetite was noticeably quieter. Then the switch happened, and Wegovy hasn't quite recreated that quiet.
The reason sits in pharmacology. Tirzepatide stimulates both the GLP-1 receptor and the GIP receptor simultaneously. Semaglutide stimulates GLP-1 only. GIP activation appears to amplify the appetite-suppression signal beyond what GLP-1 alone achieves, and the head-to-head trial evidence supports this. In the SURMOUNT-5 study, published in the New England Journal of Medicine in 2025, adults with obesity who received tirzepatide lost significantly more body weight on average than those on semaglutide 2.4mg over 72 weeks. The gap isn't trivial.
So when someone moves from the higher-performing medicine to the lower-performing one, a reduced effect isn't a sign that Wegovy is broken or counterfeit. It reflects the underlying difference in mechanism. That said, Wegovy is a genuinely effective medicine with strong evidence behind it; the STEP 1 trial in the New England Journal of Medicine reported around 15% average weight loss at 2.4mg over 68 weeks. The comparison page on how Wegovy and Mounjaro differ goes deeper on the mechanism differences if you want more detail.
The clinical question is whether the switch was medically necessary or a pragmatic one, and whether reversing it is an option.
What the numbers look like side by side
A direct comparison helps put the experience in context. These figures come from the pivotal trials; population differences mean they are not perfectly interchangeable, but they give a reasonable clinical picture.
| Factor | Mounjaro (tirzepatide) | Wegovy (semaglutide) |
|---|---|---|
| Receptor pathway | Dual: GLP-1 and GIP | Single: GLP-1 |
| Average weight loss in pivotal trial | ~20–21% at 15mg (SURMOUNT-1, NEJM) | ~15% at 2.4mg (STEP 1, NEJM) |
| Head-to-head comparison | Greater average loss (SURMOUNT-5, NEJM 2025) | Lower average loss vs tirzepatide |
| Highest licensed UK dose | 15mg | 7.2mg (single-dose pen approved April 2026) |
| UK weight-management licence | BMI ≥30, or ≥27 with a weight-related condition | BMI ≥30, or ≥27 with a weight-related condition |
The 7.2mg Wegovy dose, approved by the MHRA in April 2026, does narrow the gap somewhat — trials at that strength reported around 20.7% average weight loss, approaching tirzepatide 15mg results. If you're on a lower Wegovy maintenance dose following a switch, what to do when Wegovy isn't performing as well as Mounjaro did covers whether titrating upward is worth discussing with your prescriber. See also the NICE appraisal of semaglutide (TA875) for the full evidence base behind its UK recommendation.
Three questions worth asking before concluding the switch has failed
Not every stall after switching is a fundamental mismatch between you and Wegovy. A few things are worth ruling out first.
Are you at the right maintenance dose? Wegovy's titration schedule runs from 0.25mg to a maintenance dose, and the switch protocols vary. If the jump in dose timing wasn't matched carefully, you may not yet be at the level where the full effect is apparent. This is exactly the kind of question a prescriber reviews at each repeat; it's one reason that patients who switched and found Wegovy wasn't working are often best served by a clinical re-review rather than a quick Google.
How long has it been? Appetite suppression typically deepens over the first several weeks at each dose level. A comparison drawn at week four will look different from week twelve.
Was the switch driven by supply or by clinical recommendation? If it was supply-led, returning to Mounjaro may be straightforward. If it was clinically recommended (a cost consideration, a side-effect profile, a comorbidity), the reasons still apply. People often ask whether the reverse is worth exploring too, which tells you this is a genuinely bilateral question.
One thing the evidence is clear on: stopping either medicine tends to reverse most of the weight lost. The pattern of regain after stopping treatment is well-documented and relevant to any switch decision. Worth factoring in before concluding that discontinuing is the answer.
What a clinical review at this point looks like
The right next step is a structured conversation with a prescriber who can review your full picture: current weight, how much you lost on Mounjaro, current dose of Wegovy, how long you've been at it, and any side-effect or medical factors that drove the switch. That's different from a quick message to a general helpline.
At nume, every repeat order goes back to a named prescriber for exactly this kind of re-assessment. Transfer patients provide evidence of their current treatment so the prescriber can make an informed call, including on whether a return to tirzepatide is clinically appropriate and practically available. For a broader look at where treatment options sit, our treatment overview explains what's currently licensed and dispensed. If cost is part of why the switch happened, the price difference between Mounjaro and Wegovy sets out the honest picture. For clinical team detail, our lead prescriber's profile is there to read.
Which medicine suits you is a clinical decision our prescribers make with you, based on your history, your health and what the evidence actually shows.
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