Moving from 2.4mg Semaglutide to Tirzepatide: What the Switch Actually Involves

How the two medicines differ, and why that matters at the point of switching

Semaglutide (Wegovy) acts on a single hormone receptor: GLP-1. Tirzepatide (Mounjaro) activates two, GLP-1 and GIP. That dual action produces a somewhat different appetite-suppression and metabolic profile, which is one reason the trial results diverge. The question of switching tends to come up in one of three situations: you've reached the 2.4mg dose but weight loss has plateaued; side effects on semaglutide are persistent enough to want an alternative; or you've simply read the head-to-head evidence and want to know whether tirzepatide would do more.

Reaching 2.4mg semaglutide is significant, it's the standard maintenance dose licensed in the UK, and the dose at which trial results are typically reported. The STEP 1 trial showed around 15% average body-weight reduction over 68 weeks at that dose, published in the New England Journal of Medicine. That's a meaningful result. If you haven't achieved it, that's worth discussing with a prescriber before assuming a different medicine is the answer, adherence, diet, and other factors all play a role.

The dose equivalence question is where many people get stuck. There is no direct milligram-for-milligram conversion between the two medicines; they work differently enough that attempting to map doses numerically is misleading. A prescriber looks at your response history, tolerability, and current weight trajectory to decide where to start.

What the head-to-head evidence actually shows

The SURMOUNT-5 trial (published in the New England Journal of Medicine in 2025) ran a direct comparison between tirzepatide and semaglutide 2.4mg over 72 weeks in adults with obesity and no diabetes. Tirzepatide produced greater average weight reduction. That finding now sits inside NICE's appraisal of tirzepatide (TA1026), which noted that indirect and direct comparisons favour tirzepatide over semaglutide for weight outcomes.

The comparison is more nuanced than a single headline figure. Side-effect profiles overlap substantially, gastrointestinal effects (nausea, diarrhoea, constipation, indigestion) are common to both and typically most noticeable on starting or increasing a dose. Neither medicine is universally better tolerated. Some people find one settles faster than the other; that's an individual response, not something a trial average predicts for you specifically.

For a cleaner side-by-side view of the key clinical numbers, the table below pulls the main comparison points together.

Sources: STEP 1, NEJM; SURMOUNT-1 and SURMOUNT-5, NEJM; NICE TA1026.

What switching actually looks like in practice, and what to expect at the start

Switching from 2.4mg semaglutide to tirzepatide isn't a continuation. It's a new treatment. Most clinical guidance treats it as a restart from the lowest tirzepatide dose (2.5mg) regardless of where you were on semaglutide, allowing your system to adjust before titration begins. Your prescriber may apply a washout period between stopping semaglutide and starting tirzepatide, or may move directly; the SmPC and individual clinical judgement govern that, not a general rule.

The dosage considerations when switching are something our prescribers work through with each patient individually, taking into account how long you've been on semaglutide, what dose you're on, how you've tolerated it, and what your goals are. Transfer patients at nume provide evidence of their current treatment as part of our verification process, that's how a prescriber makes a safe, informed decision rather than guessing.

The practical side: Mounjaro arrives as a pre-filled KwikPen in a plain box, delivered to your door the next working day with a DPD tracking link. Each pen covers four weekly injections. If tirzepatide is clinically appropriate and prescribed, you'll know what to expect before it lands.

For patients thinking about cost alongside clinical factors, there's a fuller breakdown on our tirzepatide vs semaglutide cost page. Price matters, but for a prescription medicine, the right question is whether the clinical picture supports the switch, not which pen is cheaper.

Which medicine is right for you, and how that decision gets made

Neither medicine wins by default. Tirzepatide has stronger average weight-loss data in the trials. Semaglutide has a longer track record, a well-established tolerability profile, and for some patients represents unfinished business, they haven't yet reached 2.4mg or haven't given it enough time at maintenance dose. If you're already at 2.4mg semaglutide and your weight loss has genuinely stalled, that's a reasonable prompt to review. If you switched providers recently and are simply curious about tirzepatide, that's also worth discussing, but it's a different conversation.

A prescriber at nume (sorry, at nume) reviews the full clinical picture: your BMI, comorbidities, semaglutide history, current medication, and what you're trying to achieve. That review happens the same day. They may recommend continuing with semaglutide, switching to tirzepatide, or exploring something else entirely, including the broader range of weight-loss treatments. The decision isn't ours to make for you here, but you can read more about how dose considerations work in both directions and what the dose conversion process involves before your appointment.

Which medicine suits you is a clinical decision our prescribers make with you.