Switching from Mounjaro to Semaglutide: What the Dosage Shift Really Means

Why can't you just match the milligrams when switching?

It is a reasonable first question. Mounjaro (tirzepatide) activates both GIP and GLP-1 receptors; semaglutide (Wegovy) targets GLP-1 alone. Because the two medicines bind to different receptor combinations, a 7.5 mg Mounjaro dose and a 1.7 mg Wegovy dose are not equivalent in any straightforward pharmacological sense, even though both slow gastric emptying and reduce appetite. The mechanisms overlap but are not identical, and weight-loss outcomes differ accordingly.

The clinical trial data illustrate this clearly. In the SURMOUNT-5 head-to-head trial published in the New England Journal of Medicine, tirzepatide produced greater average weight reduction than semaglutide 2.4 mg over 72 weeks. NICE's appraisal of tirzepatide (TA1026) notes this when weighing indirect and direct comparisons. Moving from the more potent agent to semaglutide means most people will be stepping down in average effect, how much depends on the dose you were on and how you personally responded.

There is also a practical side to this that patients often discover late: semaglutide's titration schedule runs from 0.25 mg up through 0.5 mg, 1.0 mg, 1.7 mg and 2.4 mg over roughly four to five months. Your prescriber will judge whether to start you at the bottom of that ladder or whether a faster climb is appropriate given your history. That judgment belongs to the clinician, not to a dose chart.

What does the evidence show about each medicine's weight-loss profile?

The table below summarises the key trial-reported averages. These are population figures from controlled studies; individual results differ, and no one's outcome can be guaranteed.

Sources: NICE TA1026; SURMOUNT-1 and STEP 1, New England Journal of Medicine. It is worth noting that Wegovy's newer 7.2 mg dose, now available in a dedicated single pen, narrows the gap with tirzepatide's highest dose, a detail worth discussing with a prescriber if switching is driven by efficacy concerns.

If your interest runs the other way and you are considering switching from semaglutide to tirzepatide, the same principle applies: the prescriber reassesses from scratch rather than translating doses numerically.

What side effects should you anticipate when moving between these medicines?

Both medicines share a broadly similar gastrointestinal side-effect profile: nausea, loose stools, constipation, indigestion and fatigue are the most commonly reported, typically peaking around a dose change and settling within days to a couple of weeks. The NHS patient pages for tirzepatide and semaglutide set out the full lists.

When you switch, re-exposure to a new agent at even a low starting dose can bring a fresh wave of GI symptoms, particularly nausea. Patients who tolerated Mounjaro well sometimes find semaglutide's side-effect profile slightly different in character, and vice versa. One practical checking habit worth building: on the day you take your first new dose, write the date and your current weight in your phone's notes app. It takes thirty seconds and gives you and your prescriber a clean baseline when you next speak.

The MHRA's January 2026 Drug Safety Update on GLP-1 medicines flagged acute pancreatitis as an infrequent but serious risk across this class. Severe stomach pain that spreads to the back, with or without vomiting, warrants urgent medical attention, this guidance holds regardless of which medicine you are on. Suspected side effects from either medicine can be reported at the MHRA Yellow Card scheme.

How does a prescriber decide which dose to start you on after switching?

There is no published conversion chart endorsed by UK regulators for moving between tirzepatide and semaglutide. A prescriber weighs several things: how long you were on Mounjaro, which dose you reached, how your body responded, any side-effect history, and your current weight and health picture. For most people switching to Wegovy, starting at the lowest dose and titrating methodically is the safer path, even if it feels like going backwards.

The question of what semaglutide dose is equivalent to Mounjaro comes up often in our prescribers' inboxes, and the honest answer is that equivalence is approximate at best. Anyone offering a neat conversion table as clinical fact is overstating what the evidence supports. A detailed overview of how the two medicines compare across price, availability and clinical profile is covered on the Wegovy vs Mounjaro page.

If cost is part of what is driving the switch, the UK price comparison between Mounjaro and Wegovy sets out what the market currently looks like honestly and factually. And if you are mid-treatment on a specific dose (say, switching from 7.5 mg Mounjaro or moving in the opposite direction from Wegovy 2.4 mg) the dose-specific pages go into the practical detail. Which medicine suits you at this point in your treatment is a clinical decision our prescribers make with you, not a matrix you can resolve alone.