Mounjaro not working: is switching to Wegovy the right move?

The biggest misconception: that a stronger medicine fixes a plateau

Many people assume that if one GLP-1 medicine has stopped working, moving to a different one will restart progress. That is the misconception worth correcting first. Wegovy (semaglutide) and Mounjaro (tirzepatide) work through related but different mechanisms. Mounjaro activates both GIP and GLP-1 receptors; Wegovy targets GLP-1 alone. The head-to-head data, from the STEP 1 trial for semaglutide and SURMOUNT-5 for tirzepatide, consistently shows tirzepatide producing larger average weight reductions. Switching from a dual-agonist to a single-agonist is not a clinical step forward on paper.

What actually causes a plateau or poor response on Mounjaro is usually one of a handful of things: the dose has not reached the level where the medicine is doing its full job; lifestyle factors such as protein intake or sleep have not shifted enough to work alongside reduced appetite; or an underlying condition (thyroid function, insulin resistance, certain medications) is blunting the response. A plateau is a signal to investigate, not to swap.

That said, individual responses vary considerably. Some people tolerate Mounjaro poorly, or find its side-effect profile difficult at higher doses. In those cases, a prescriber may consider semaglutide, and if you are in that position it is worth reading about what happens when Wegovy is not working after Mounjaro before drawing conclusions. The decision belongs in a clinical conversation, not in a forum thread. Our Wegovy vs Mounjaro comparison covers the evidence in full if you want to read the data before that conversation.

What the trial numbers actually show side by side

It helps to see the figures in one place. The table below draws from the SURMOUNT-5 head-to-head and the licensed trial programmes for each medicine, as discussed in NICE technology appraisal TA1026.

The 7.2 mg Wegovy dose narrows the gap in trial data (around 20.7% average weight loss over 72 weeks) but it was approved in the UK only in April 2026 and long-term real-world data is still accumulating. These are population averages; your prescriber looks at your individual picture. If you want to understand why Wegovy tends to produce less weight loss than Mounjaro for most people, that page goes deeper on the mechanism.

When switching might be the right clinical call

There are genuine reasons a prescriber might move someone from Mounjaro to Wegovy, or vice versa. Persistent intolerance to Mounjaro at doses below therapeutic effect is one. A supply issue affecting one medicine is another. Occasionally, a patient's comorbidity profile makes one molecule preferable, and the MHRA-approved cardiovascular indication for semaglutide (Wegovy) is a factor some prescribers weigh. Cost is a consideration too; the price difference between Mounjaro and Wegovy is not trivial at the higher doses.

One practical check you can do in under a minute: look at the injection date log in your phone or diary and count how many consecutive weeks you reached the same dose before the plateau appeared. If it was fewer than eight weeks at that dose, the medicine may simply not have reached steady state yet. That information is useful to share at your next clinical review.

Switching carries its own reset. People who move from Mounjaro to Wegovy often restart at a low dose and re-titrate, which means weeks at sub-therapeutic levels. Our page on Wegovy not working after switching from Mounjaro explains what to expect during that period. And if the concern runs deeper (specifically around weight returning when either medicine is paused) the evidence on weight regain after stopping treatment is worth reading before making any change.

Which medicine suits you is a clinical decision. Our prescribers work through exactly this kind of question with patients every day. Start your free consultation and a named GPhC-registered prescriber will review your situation the same day.