Mounjaro to Wegovy: Why There Is No Dose Conversion

There is no dose conversion chart between Mounjaro and Wegovy, because they are different molecules: tirzepatide acts on two receptors (GIP and GLP-1) and semaglutide on one (GLP-1). So your Mounjaro dose does not translate into an equivalent Wegovy dose. Switching means starting Wegovy's own escalation from its low starting dose and titrating up, decided and supervised by a prescriber. This guide explains why, and what switching actually involves.

If you are looking for a chart that converts your Mounjaro dose into the 'equivalent' Wegovy dose, the most important thing to know is that no such chart exists, and that is not an oversight. The two medicines are different molecules, so there is no milligram-for-milligram equivalence to convert between, and treating them as interchangeable would be unsafe.

This guide explains why there is no conversion, how the two differ, and what switching between them actually involves in practice, which is a fresh start on Wegovy's own escalation under a prescriber. It draws on the UK Summaries of Product Characteristics and the NHS, and it is general information; any switch is a clinical decision made with the prescriber who knows your case.

Why there is no conversion chart

The reason a conversion chart does not exist is fundamental to what these medicines are: Mounjaro is tirzepatide and Wegovy is semaglutide, two different active substances ¹². A dose conversion only makes sense between the same substance in different forms, not between two distinct molecules with their own dosing schemes ¹².

Each medicine has its own escalation schedule and its own maintenance doses, set out separately in its own product information, and the milligram numbers are not comparable across them ¹². A 'high' dose of one is not the same as a 'high' dose of the other, because the numbers refer to different substances doing the job in different ways ¹².

So any chart claiming to convert a Mounjaro dose into an equivalent Wegovy dose would be inventing an equivalence that does not exist, and following it could mean starting at an inappropriate dose ². The safe and accurate position is that there is no conversion: a switch is a fresh start on the new medicine's schedule, not a translation of the old dose ²³.

How the two molecules actually differ

Tirzepatide, the active substance in Mounjaro, acts on two receptors, GIP and GLP-1¹. Semaglutide, the active substance in Wegovy, acts on one, the GLP-1 receptor ². That difference in mechanism is one reason they are genuinely different medicines rather than two versions of the same thing ¹².

They also differ in their dosing details, with their own starting doses, their own step-by-step escalation intervals and their own maintenance doses, each defined in its own SmPC ¹². Our guide comparing Mounjaro and Wegovy covers how they compare more broadly ¹².

Because of all this, the experience of one does not predict the experience of the other in a simple way ¹². Side effects, tolerability and response can differ between the two, which is part of why a switch is approached as starting a new treatment rather than continuing the old one at a 'matching' dose ¹².

What switching actually involves

In practice, switching from Mounjaro to Wegovy means starting Wegovy at its own low starting dose and following its own escalation upwards, exactly as someone beginning Wegovy would, rather than jumping in at a dose matched to your old Mounjaro dose ²³. This is what protects tolerability on the new medicine ².

The reason is the same as for anyone starting a GLP-1 medicine: beginning low and increasing gradually helps the body adjust and manages gastrointestinal side effects ². Skipping that because you were already on a different medicine at a higher number would not be safe, because the new molecule needs its own introduction ².

How exactly a switch is handled, including timing and starting point, is a clinical decision for your prescriber, who will base it on your circumstances ²³. This is not something to attempt by self-converting a dose or sourcing medicine independently; it needs proper supervision ².

Considering treatment for weight management? You can start an assessment with a Cloud Pharmacy clinician, who will review your medical history and confirm whether treatment is appropriate.

Why people look for a conversion, and a better question

The search for a conversion chart usually comes from a reasonable place: people want to switch without losing progress or facing side effects again, and a neat chart feels reassuring ². Understanding why there is not one actually helps, because it sets the right expectation for how a switch works ²³.

A more useful question than 'what is my equivalent dose?' is 'how should this switch be managed for me?' ²³. That reframes it as the clinical decision it really is, covering why you are switching, how to start the new medicine safely, and what to expect during the new escalation ²³.

It also helps to expect that the early weeks on Wegovy may bring some of the adjustment you remember from starting Mounjaro, because the new molecule has its own settling-in period ². That is normal and is the trade-off for switching safely, rather than a sign something has gone wrong ².

Doing it safely

The safe way to switch is entirely through a registered pharmacy or service with a prescriber, who assesses whether switching is right for you and manages how it is done ²³. The NHS warns that some websites sell fake weight-loss medicines, so sourcing either medicine outside a registered route to manage a switch yourself is exactly the risk to avoid ².

Be especially wary of any source that offers a 'conversion dose' of Wegovy matched to your Mounjaro dose, because that is medically inaccurate and a sign of an unsafe seller rather than a helpful shortcut ². A legitimate switch starts Wegovy on its own schedule, full stop ²³.

If you are considering switching, the right next step is a conversation with a prescriber about why and how, not a search for a chart ²³. Our guide on Mounjaro versus Wegovy can help you think through the comparison before that conversation ¹².

The takeaway in one line

The single thing to remember is that there is no dose conversion between Mounjaro and Wegovy, because they are different molecules with their own separate dosing ¹². Your Mounjaro dose does not map onto a Wegovy dose ¹².

Switching means starting Wegovy at its own low starting dose and titrating up under a prescriber, just as anyone beginning Wegovy would, and accepting that the new medicine has its own introduction ²³. That is the safe, accurate picture ².

So treat any 'conversion chart' you come across with suspicion, ask your prescriber how a switch should be managed for you, and only ever use a registered route ²³. That approach protects both your safety and your progress far better than a chart that promises an equivalence the science does not support ¹².

What to expect during the change

It helps to go into a switch with realistic expectations about the early weeks ². Because you are starting the new medicine at its low starting dose and building up, the appetite effect you had become used to on your previous medicine may feel different, or less strong, until the new dose has been escalated over the following weeks ²³. That is expected and is part of starting any GLP-1 medicine, not a sign the switch has failed ².

Some people also notice the return of early side effects such as nausea as the new molecule is introduced and the dose climbs ². The same practical steps that help anyone starting out apply here: smaller, less rich meals, eating slowly, and staying hydrated, with your prescriber to turn to if anything is troublesome ². Our guide on managing nausea and gut symptoms is worth a look during the change ².

Because the trajectory restarts, it is worth resisting the temptation to judge the new medicine too quickly ²³. Give the escalation time to reach a maintenance dose before drawing conclusions, and bring any concerns to a review rather than acting on them alone ²³. A switch is a transition to manage patiently, not an instant swap ².

Keeping your prescriber informed throughout is what makes the change go smoothly ²³. They can adjust the pace of the new escalation, advise on timing, and make sure the transition fits your circumstances, which is exactly the kind of supervision a switch needs and that no chart could ever provide ².

It is also worth being clear with yourself about why you are switching in the first place, because that helps your prescriber make the right call ²³. Whether it is side effects, cost, supply, or how a medicine suits you, naming the reason turns the conversation into a proper clinical decision about whether Wegovy is likely to serve you better, rather than a mechanical swap, and it means the switch is made for a sound reason rather than on impulse ²³.

Finally, do not let the absence of a conversion chart put you off raising a switch if there is a good clinical reason for one ²³. The point of this guide is not that switching is wrong, but that it is done properly through a fresh, supervised start on the new medicine rather than by converting a dose, and a prescriber can make that change safe and straightforward for you ². With the right reason and proper supervision, switching is a routine clinical decision, not something to be anxious about ²³.

Frequently asked questions

Is there a Mounjaro to Wegovy dose conversion chart?

No. They are different molecules, tirzepatide and semaglutide, with their own separate dosing, so there is no equivalence to convert between ¹². Switching means starting Wegovy on its own escalation, not matching your Mounjaro dose ²³.

Why can't I just start Wegovy at a dose matching my Mounjaro dose?

Because the milligram numbers refer to different substances and are not comparable, so a 'matching' dose is medically meaningless and could be inappropriate ¹². Wegovy is started low and titrated up to protect tolerability, like any new GLP-1 medicine ².

What does switching from Mounjaro to Wegovy involve?

Starting Wegovy at its own low starting dose and following its own escalation upwards, supervised by a prescriber who decides if and how to switch based on your circumstances ²³. Expect a settling-in period on the new molecule ².

Will I lose my progress by restarting the dose on Wegovy?

Starting Wegovy on its own schedule is how a switch is done safely, and it is a clinical decision made with your prescriber to manage the transition ²³. The early weeks may bring some adjustment, which is normal rather than a sign of lost progress ².

Can I manage the switch myself?

No. A switch should go through a registered pharmacy or service with a prescriber, who assesses suitability and manages it ²³. The NHS warns some websites sell fake weight-loss medicines, so sourcing medicine to self-switch is exactly the risk to avoid ².

Why do the two medicines need different dosing?

Tirzepatide acts on two receptors, GIP and GLP-1, and semaglutide on one, GLP-1, so they are genuinely different medicines with their own dosing schemes ¹². That is why one's dose cannot be converted into the other's ¹².

Your next step

There is no dose conversion chart between Mounjaro and Wegovy, and that is because they are different molecules, tirzepatide acting on two receptors and semaglutide on one, each with its own separate escalation and maintenance doses. Your Mounjaro dose does not translate into an equivalent Wegovy dose, and any chart claiming otherwise is inventing an equivalence that the science does not support.

Switching in practice means starting Wegovy at its own low starting dose and titrating up under a prescriber, exactly as anyone beginning Wegovy would, and accepting a settling-in period on the new molecule. Treat any 'conversion dose' offer as a warning sign, use only a registered pharmacy or service, and ask your prescriber how a switch should be managed for you rather than searching for a chart. That protects both your safety and your progress far better than a false equivalence ever could.

Disclaimer

This guide is for general information only and does not constitute medical advice, diagnosis or treatment. The information here describes general clinical context based on UK regulatory sources cited above; it is not a recommendation for any specific medicine or treatment, which can only be made by a prescriber following individual assessment.

If you are considering treatment, speak to your GP or pharmacist, or arrange a consultation with a Cloud Pharmacy clinician. Prescription-only medicines are issued only after clinical assessment and where appropriate.

If you experience side effects from any medicine, you can report them through the Yellow Card scheme at yellowcard.mhra.gov.uk.

References

1. Mounjaro SmPC 4.2/5.1 (tirzepatide; dual GIP/GLP-1 receptor agonist; its own escalation and maintenance doses, distinct from semaglutide; no cross-product dose equivalence)
2. Wegovy SmPC 4.2/5.1 (semaglutide; GLP-1 receptor agonist; its own low starting dose and escalation; titrate up to manage tolerability; started on its own schedule regardless of prior medicine)
3. Tirzepatide/semaglutide (registered pharmacy; prescriber supervision; some websites sell fake weight-loss medicines; do not change medicine or dose without advice)