Side Effects of Moving from Mounjaro to Wegovy: What Actually Happens

The biggest misconception: that your side effects will be lighter because semaglutide is a 'weaker' medicine

The assumption many people arrive with is that moving to Wegovy should feel easier because tirzepatide is sometimes described as the more potent of the two. In practice, that logic does not hold. Side effects with GLP-1 medicines are not a straightforward function of efficacy, they depend on which receptors are being activated, your personal gastrointestinal sensitivity, and critically, where you land in the dose schedule when you restart.

Mounjaro activates both GIP and GLP-1 receptors. Wegovy works on GLP-1 receptors only. When you switch, you are not continuing the same pharmacological signal at a lower intensity; you are changing the signal itself. Some people find semaglutide produces more pronounced nausea than they experienced at equivalent stages on tirzepatide. Others notice the reverse. If you want to understand what that change in signal can mean in practice, our page on switching from Mounjaro to Wegovy side effects covers what people commonly report during that transition. The NHS medicines page for semaglutide lists the most commonly reported effects as nausea, vomiting, diarrhoea, constipation, and stomach discomfort, a profile that overlaps substantially with tirzepatide but sits on a different biological footing.

The dose you restart on matters enormously. A prescriber will typically require you to begin Wegovy's titration schedule from a low starting dose rather than matching your last Mounjaro strength, and that restart is itself protective. Questions about exactly where to enter the schedule are for your prescriber and the Patient Information Leaflet, not a general guide.

For a fuller picture of how the two medicines compare across effectiveness and tolerability, our Wegovy vs Mounjaro side effects page covers the broader data in detail.

What the evidence actually shows about tolerability differences

Direct head-to-head tolerability data between the two medicines is limited. The SURMOUNT-5 trial (New England Journal of Medicine, 2025) compared tirzepatide and semaglutide 2.4mg in adults with obesity and found tirzepatide produced greater average weight reduction, but SURMOUNT-5 was not designed to rank tolerability, so drawing firm conclusions about which causes fewer side effects from that trial alone would be an overreach.

What the individual trial programmes do show is that gastrointestinal side effects are the most common category for both medicines. In STEP 1, nausea affected roughly 44% of semaglutide participants versus about 16% in the placebo group. SURMOUNT-1 data showed a broadly similar GI-led pattern for tirzepatide. Both medicines produce effects that are most noticeable after starting or after a dose increase, and that generally settle within days to two weeks as the body adjusts.

The practical implication for someone switching: the first few weeks on Wegovy may feel like a second adjustment period, separate from anything experienced on Mounjaro. That is not a sign the switch has gone wrong. It is the expected response to a new molecule starting its titration. A habit worth building early (checking in with yourself on a specific morning each week, noting any symptoms briefly) makes it far easier to describe patterns accurately if your prescriber asks.

The Mounjaro and Wegovy side effects page sets out each medicine's profile side by side in more depth.

A factual comparison of the key side-effect differences

The table below summarises the most clinically relevant points of difference and similarity based on the licensed product information and published trial data. It is a factual reference, not a basis for self-prescribing decisions.

Because the oral contraceptive interaction differs between the two medicines, anyone switching who uses the pill should flag this directly with their prescriber before their first Wegovy dose. The NHS England guidance on weight-management injections covers the contraception and HRT points relevant to both medicines.

For context on how costs compare across the two treatments, the tirzepatide vs semaglutide cost page sets that out clearly.

What to discuss with a prescriber before switching

No switch between these medicines should happen without a clinical assessment. The prescriber needs to understand why you are considering the change, whether that is inadequate weight loss, specific side effects you found difficult, supply, cost, or a personal preference for the injection format. Each reason points to a different clinical conversation.

Bring any symptom history you have: which side effects you experienced on Mounjaro, at which doses, and how they resolved (or did not). This gives the prescriber a much clearer picture of your GI sensitivity and helps them judge where to start you on Wegovy's titration schedule. Transfer patients at nume are asked to provide evidence of their current treatment and dose history, this is standard clinical practice, not extra bureaucracy.

If you have been on Mounjaro at a higher dose, a prescriber may also want to discuss the washout considerations, since the two medicines work on overlapping pathways. There is no one-size answer here; it depends on your response to treatment so far.

Our guide to changing from Mounjaro to Wegovy covers the practical steps in more detail. You can also explore the full range of treatment options on the weight loss treatments page, or read about the wider comparison between these two medicines on our Wegovy vs Mounjaro overview. Which medicine suits your situation is a clinical decision our prescribers make with you.