Switching from Semaglutide to Tirzepatide: What the Dosage Change Actually Means

The myth worth clearing up first: there is no simple dose-conversion chart

A common assumption is that switching from semaglutide to tirzepatide follows a fixed formula — that 2.4mg of semaglutide equals a specific tirzepatide dose, and you simply slot in at the equivalent rung. That assumption is understandable, and it's also incorrect. The two medicines act on different receptors: semaglutide activates the GLP-1 receptor alone, while tirzepatide activates both the GLP-1 and GIP receptors. Because the pharmacological targets differ, a milligram figure on one scale tells you nothing reliable about the appropriate starting point on the other.

That's worth sitting with for a moment, because people who've been on semaglutide for some time (and who've built up to 1.7mg or 2.4mg) sometimes worry they'll be "going backwards" by starting tirzepatide at 2.5mg. The concern is genuine, but the framing isn't quite right. The 2.5mg starting dose of tirzepatide exists to let your system adjust to a new mechanism, not to mark a lower level of treatment. Your prescriber will consider your full history when timing any increases. If you're curious about how patients moving from a higher semaglutide dose approach this, the detail on switching from 2.4mg semaglutide to tirzepatide covers that specific transition.

Published guidance does not provide a formal switching dosage chart between the two medicines, and the NICE appraisals for tirzepatide (TA1026) and semaglutide treat them as independent treatment pathways. The Mounjaro SmPC on the eMC does not list semaglutide doses as reference points for starting dose selection.

What a prescriber weighs up when you switch

Because no validated conversion table exists, the clinical assessment at the point of switching draws on several factors rather than a single number. How long you were on semaglutide matters, as does the dose you reached and how well you tolerated it. Your weight at the time of switching, any weight-related conditions, and the reason for switching (whether that's insufficient response, tolerability problems, or a preference for the dual mechanism) all feed into the decision.

Most people switching from semaglutide begin tirzepatide at 2.5mg, irrespective of the semaglutide dose they were on. This is the licensed starting point under the Mounjaro SmPC, and the titration schedule then progresses in 4-weekly steps at the prescriber's discretion. If you were previously on 1mg semaglutide, our page on making the move from 1mg semaglutide to tirzepatide walks through what that transition typically involves. There is some clinical discussion about whether patients who tolerated higher semaglutide doses well might move through early tirzepatide steps more quickly, but that is a prescriber judgement, not a self-directed decision.

The semaglutide-equivalent dose to tirzepatide page explores the evidence base for this question in more depth. For patients moving in the opposite direction, the considerations are different, our page on switching from Mounjaro to semaglutide covers that scenario.

Comparing semaglutide and tirzepatide: what the trial evidence says

Setting aside the switching mechanics, it helps to understand how the two medicines compare on outcomes. The table below draws on published trial data and NICE appraisal materials.

The SURMOUNT-5 head-to-head trial involved 751 adults with obesity and no diabetes, and over 72 weeks tirzepatide produced greater average weight loss than semaglutide 2.4mg. That result is meaningful context, but it reflects group averages. Individual response varies, and a higher average does not mean tirzepatide will suit every person better. Our Wegovy vs Mounjaro comparison sets out the full picture without declaring a winner.

Side effects to be aware of when switching

Both medicines share a broadly similar side-effect profile, driven by their shared GLP-1 pathway: nausea, loose stools, constipation, and indigestion are the most commonly reported, particularly in the early weeks or after a dose increase. Because tirzepatide is a new medicine to your system, these effects may return even if you'd largely settled on semaglutide, especially in the first few weeks of the 2.5mg starting dose.

The January 2026 MHRA Drug Safety Update for GLP-1 medicines flagged acute pancreatitis as an infrequent but serious risk: severe stomach pain that radiates to the back, with or without vomiting, requires urgent medical attention. This applies to both semaglutide and tirzepatide. Women taking oral contraceptives should be aware that tirzepatide can reduce pill absorption, a non-oral method is recommended for the first four weeks of treatment and for four weeks after each dose increase, as noted in NHS England's guidance on weight-management injections.

Side effects, timing questions, and anything about how your body is responding belong in a conversation with your prescriber. If something feels urgent, seek medical help promptly. You can also report suspected side effects via the MHRA Yellow Card scheme. Our support team is available seven days a week for aftercare questions.

Which medicine is the right choice (and at what starting point) is a clinical decision our prescribers reach with you individually, not a number you can calculate in advance. Patients who were on 1.7mg semaglutide before switching will find guidance tailored to their situation on our page covering the transition from 1.7mg semaglutide to tirzepatide.