If Mounjaro Doesn't Work, Will Wegovy — or Vice Versa?

The myth: if one GLP-1 fails, the whole class fails

This is the misconception most worth correcting first. People assume that because Mounjaro and Wegovy are both injected weight-loss medicines, they work in identical ways, so failure with one means failure with both. That isn't accurate. Wegovy (semaglutide) activates GLP-1 receptors, the gut-hormone pathway involved in appetite and satiety. Mounjaro (tirzepatide) does that too, but it also activates a second receptor (GIP) making it a dual-agonist. If you're wondering whether Wegovy works the same as Mounjaro, the honest answer is that these are genuinely different pharmacological profiles. A body that responded poorly to semaglutide's single-pathway approach may respond differently to tirzepatide's two-receptor action, and vice versa.

There is also the question of tolerability versus efficacy. Sometimes treatment is stopped not because weight loss is absent, but because side effects (typically nausea, diarrhoea or reflux) became too difficult to manage at the doses needed. One medicine's GI burden can differ meaningfully from the other's for a given person. If you've had a poor experience with one and want to understand whether Wegovy might still work if Mounjaro didn't, that's a question worth exploring with a prescriber rather than assuming the answer is no. So "didn't work" is worth unpacking: was it the effect on weight, or the effect on your stomach?

Either way, the answer isn't to guess. A prescriber reviewing your treatment history (including how long you tried the first medicine, what dose you reached, and what symptoms you experienced) is the right starting point. Our clinical team handles exactly these conversations.

What the trial data shows about each medicine's ceiling

The SURMOUNT-1 trial, published in the New England Journal of Medicine, found average body-weight reductions of around 20–21% at tirzepatide's 15mg maintenance dose over 72 weeks. The STEP 1 trial, also published in the New England Journal of Medicine, reported around 15% average reduction with semaglutide 2.4mg over 68 weeks. In the SURMOUNT-5 head-to-head trial (72 weeks, adults with obesity, no diabetes), tirzepatide produced greater average weight loss than semaglutide 2.4mg, a result cited in NICE's appraisal of tirzepatide (TA1026). More recently, the higher 7.2mg Wegovy dose reported around 20.7% average loss at 72 weeks, narrowing that gap considerably.

These are population averages from controlled trials. Individual responses vary substantially. Some people lose far less than the trial average; a minority lose considerably more. If your weight loss on Mounjaro stalled well below the clinical trial range, and you reached the highest tolerated dose, the evidence on whether Wegovy works after Mounjaro suggests that switching, rather than assuming the class has failed, is a reasonable question to put to a prescriber.

A quick check worth doing before any appointment: note the highest dose you actually reached and roughly how many weeks you spent there. That single piece of information changes the clinical conversation considerably.

How Mounjaro and Wegovy compare side by side

The table below covers the main factual differences. It is not a ranking, which medicine is right for a given person depends on health history, tolerability and a prescriber's assessment.

For a fuller breakdown of how the two medicines differ in mechanism and practice, the page on what Mounjaro does that Wegovy doesn't goes into that in detail. If you've already tried Wegovy and are curious about how closely Wegovy works like Mounjaro in terms of the underlying mechanisms, that dedicated page covers the specific switching evidence.

Switching in practice: what a clinical review actually looks at

A prescriber considering a switch will want to know more than "it didn't work". Duration on the previous medicine, the highest dose reached and tolerated, the nature of any side effects, your current weight relative to your starting point, and any changes in your health since treatment began all factor in. Stopping one medicine and starting another also involves a washout or transition window that the prescriber will manage. The question of going straight from Mounjaro to Wegovy is one our clinical team fields regularly, and the short answer is that the timing depends on your specific situation. You shouldn't self-manage that transition.

Both medicines are also available only on prescription following clinical assessment, the NHS medicines page for tirzepatide and the equivalent page for semaglutide confirm this, and neither is suitable for everyone. History of medullary thyroid carcinoma, MEN2, certain GI conditions or pancreatitis requires careful discussion. Pregnancy, breastfeeding and trying to conceive rule both medicines out. People under 18 are not licensed to use either.

At nume, every treatment change (including a switch from one injection to another) goes through the same same-day clinical review that a first prescription does. You can read more about how our service works on the about us page, and our clinical team handles transfer and switch consultations directly. Which medicine suits you is a clinical decision our prescribers make with you, not a choice we'd ask you to make alone.

Ready to discuss your options? Speak to our prescribers with a free consultation.