Can I just swap one for the other at the same dose?

No. There is no dose-for-dose swap. They are different medicines, and the mg numbers do not line up. A switch means your prescriber decides the starting dose on the new medicine, usually beginning low and stepping up, rather than continuing at the same number you were on.

Why do people switch?

The common reasons are side effects that are hard to manage, weight loss slowing or plateauing, cost, and supply problems. Which one suits a person is an individual decision for their prescriber, not something to judge from a comparison alone.

Which one causes more weight loss?

In SURMOUNT-5, the first head-to-head trial, average weight loss over 72 weeks was 20.2% with tirzepatide (Mounjaro) versus 13.7% with semaglutide (Wegovy). It was an open-label trial funded by the maker of tirzepatide. Trial averages are not a prediction for any one person, and more weight loss is not automatically the right choice for you.

Will the side effects start again if I switch?

Usually yes, to a degree. Because you start the new medicine at a low dose and step up, the stomach side effects that come with a dose increase can return for a while as your body adjusts, then settle.

Switching between Mounjaro and Wegovy

People move between these medicines for side effects, a plateau, cost or supply. They are not interchangeable at the same dose, and the switch itself is a decision for your prescriber. Here are the facts to take into that conversation.

Last updated 3 November 2026

The short version

They are different medicines: there is no dose-for-dose swap.
A switch means starting low on the new one and stepping up, decided by your prescriber.
Expect the step-up side effects to return for a while, then settle.
The change is a prescriber decision. Do not overlap or self-adjust.

They are different medicines

Mounjaro is tirzepatide, which acts on two gut hormone receptors (GIP and GLP-1). Wegovy is semaglutide, which acts on one (GLP-1). Because they are different molecules, the dose numbers do not translate between them, so you cannot match, for example, a 10 mg of one to a dose of the other. See the facts side by side in the Mounjaro vs Wegovy comparison.

What a switch actually involves

A switch is not continuing at the same number. Your prescriber sets a starting dose on the new medicine, usually the lowest, and steps it up over the following weeks, the same way you began the first one. Pens, how often you inject and storage can differ too, so treat it as starting a new medicine rather than a sideways move.

Why people switch

Side effects that are hard to manage on one medicine.
A plateau, where weight loss has slowed or stopped.
Cost: prices differ, so see what they cost.
Supply: if one is hard to get, see what to do.

What the head-to-head trial found

In SURMOUNT-5, the first trial to compare them directly, average weight loss over 72 weeks was 20.2% with tirzepatide and 13.7% with semaglutide. It was an open-label trial funded by the maker of tirzepatide. A trial average is not a prediction for any one person, and it does not mean more weight loss is the right choice for you. How people respond, and tolerate, varies a lot.

How to switch safely

Talk to your prescriber. They will decide the starting dose, when to stop the current medicine and when to begin the new one, so that you do not double up. Do not run the two together or change doses yourself. If you are switching provider at the same time, check the new provider is on the register first.

Common questions

Can I just swap one for the other at the same dose?: No. There is no dose-for-dose swap. They are different medicines, and the mg numbers do not line up. A switch means your prescriber decides the starting dose on the new medicine, usually beginning low and stepping up, rather than continuing at the same number you were on.
Why do people switch?: The common reasons are side effects that are hard to manage, weight loss slowing or plateauing, cost, and supply problems. Which one suits a person is an individual decision for their prescriber, not something to judge from a comparison alone.
Which one causes more weight loss?: In SURMOUNT-5, the first head-to-head trial, average weight loss over 72 weeks was 20.2% with tirzepatide (Mounjaro) versus 13.7% with semaglutide (Wegovy). It was an open-label trial funded by the maker of tirzepatide. Trial averages are not a prediction for any one person, and more weight loss is not automatically the right choice for you.
Will the side effects start again if I switch?: Usually yes, to a degree. Because you start the new medicine at a low dose and step up, the stomach side effects that come with a dose increase can return for a while as your body adjusts, then settle.

Sources

From the UK SmPCs and the published trials as of 3 November 2026. This is educational reference, not medical advice, and it does not recommend a medicine. Any change is a decision for your prescriber.