Switching from Wegovy to Mounjaro: what you need to know

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Thinking of switching from Wegovy to Mounjaro? Learn the key differences, side effects and how treatment transitions are managed safely.

Wegovy (semaglutide) and Mounjaro (tirzepatide) are two of the most widely used medications for weight loss. Both are designed to support people living with obesity by reducing appetite and helping to maintain a sustainable calorie deficit over time.

If you're currently taking Wegovy, you may wonder whether switching to Mounjaro is possible, or even if it might offer additional benefits.

While the two medications are similar in many ways, there are some important differences to consider. That includes:

How they work
How they're dosed
How switching between them is managed

How Wegovy and Mounjaro work

Wegovy and Mounjaro both act on hormones involved in appetite regulation. However, they are not identical.

Wegovy is a GLP-1 receptor agonist. It mimics the action of a hormone called 'glucagon-like peptide-1' (GLP-1), which helps to reduce appetite, increase feelings of fullness, and slow gastric emptying.

Mounjaro, on the other hand, is a dual GIP and GLP-1 receptor agonist. In addition to targeting GLP-1, it also activates receptors for a hormone called 'glucose-dependent insulinotropic polypeptide' (GIP).

This dual action may enhance its effects on appetite regulation, blood sugar control and energy balance.

While both medications support weight loss in similar ways, this difference in mechanism is one of the main reasons people consider switching to Mounjaro.

How effective are they?

Both Wegovy and Mounjaro are shown to support significant weight loss when combined with lifestyle changes.

In clinical trials:

Mounjaro users lost an average of 21% of their starting body weight over 72 weeks¹
Wegovy users lost an average of 15% over 68 weeks²

These results reflect average outcomes across large groups of participants. Individual results can vary depending on factors such as lifestyle, overall health and adherence (how closely you stick to the treatment plan).

While Mounjaro has shown higher average weight loss in trials, this doesn't necessarily mean it will be more effective for everyone. The best option depends on how your body responds to each medication and your tolerance of side effects.

Differences in dosage and administration

Both medications are taken as a once-weekly injection, using a pre-filled pen device. However, their dosing schedules differ slightly.

Wegovy dosing

Wegovy is typically started at a low dose (0.25mg) and gradually increased over several weeks to reduce the risk of side effects. Most people will go through five different dose levels before reaching a maintenance dose of 2.4mg.

Weeks 1 to 4: 0.25mg
Weeks 5 to 8: 0.5mg
Weeks 9 to 12: 1mg
Weeks 13 to 16: 1.7mg
Week 17+: 2.4mg

Mounjaro dosing

With Mounjaro, you also take a gradually increasing dose. However, these doses are different, and there is a wider range of doses available.

Weeks 1 to 4: 2.5mg
Weeks 5 to 8: 5mg
Weeks 9 to 12: 7.5mg
Weeks 13 to 16: 10mg
Weeks 17 to 20: 12.5mg
Week 21+: 15mg

More doses can mean more flexibility. There's more room for your healthcare team to personalise your dose, depending on how you tolerate the medication and how well it works for you.

Side effects and tolerability

Wegovy and Mounjaro have very similar side effect profiles, as both affect the digestive system.

Common side effects, particularly in the early stages of treatment, can include:³ ⁴

Nausea
Vomiting
Diarrhoea
Constipation
Reduced appetite

However, while the common side effects are very similar, Mounjaro users may experience certain side effects that are much rarer with Wegovy.

For instance, on rare occasions, Mounjaro users may experience hair thinning. Mounjaro is also known to make the contraceptive pill work less effectively, while this isn't a recognised risk for Wegovy.

On the other side of the coin, some people find Mounjaro easier to tolerate than Wegovy in terms of side effects. It's all about what works best for you and your body.

Learn more about the side effects of Wegovy and Mounjaro.

Why might someone switch from Wegovy to Mounjaro?

There are several reasons why someone may consider switching from Wegovy to Mounjaro.

1. Weight loss plateaus

If weight loss has slowed or stopped, a clinician may review treatment options.

2. Side effects

If side effects are difficult to manage, trying an alternative medication may be appropriate.

3. Treatment goals

Some individuals may be aiming for further weight loss or improved metabolic outcomes.

4. Clinical recommendation

A healthcare provider may suggest switching based on your overall progress and response to treatment.

How does switching work?

Switching between GLP-1-based medications is not simply a case of stopping one and starting another at a full dose.

In most cases, your clinician will:

Review your current dose and response.
Consider any side effects you've experienced.
Decide on an appropriate starting dose for the new medication.

You will usually start Mounjaro at a lower dose, even if you've been taking a higher dose of Wegovy. This helps to minimise the risk of developing new side effects.

There will also be a short gap between treatments. At Semapen, we recommend a gap of at least 10 days between your last dose of Wegovy and your first dose of Mounjaro.

The exact approach can vary from person to person, which is why switching should always be done under medical supervision.

Do you have to 'start again'?

In a sense, yes – but not always entirely.

Although your body is already used to a GLP-1 medication, Mounjaro has a slightly different mechanism of action. Starting at a lower dose allows your body to adjust safely.

However, your previous experience with Wegovy is still valuable. It can help inform:

How quickly doses are increased.
How side effects are managed.
What level of support you need.

So, while the dosing may restart at a lower level, your treatment plan remains personalised.

What stays the same?

Despite their differences, Wegovy and Mounjaro share several key similarities.

Both medications:

Are taken as once-weekly injections
Work by reducing appetite and supporting a calorie deficit
Require gradual dose increases
Are most effective when combined with lifestyle changes

Crucially, neither of these medications replaces the need for a healthy, balanced diet and regular physical activity. Instead, they support these changes by making them easier to maintain.

Support during the transition

Switching weight loss medication is more than just a clinical decision. It's part of a broader treatment journey tailored to you.

At Semapen, we review treatment plans on a case-by-case basis. That means reviewing your progress so far and any side effects, as well as your goals and preferences.

If a switch is appropriate, you'll be supported throughout the process, with guidance on dosing, side-effect management and ongoing care.

Wegovy and Mounjaro are both effective, evidence-based treatments for weight loss, with similar mechanisms but some important differences.

Mounjaro's dual action on GLP-1 and GIP receptors may offer additional benefits for some individuals, including potentially greater average weight loss.

The decision to switch medications should always be made with clinical guidance, taking your individual response and treatment goals into account.

With the right clinical support, switching medications can be a smooth and well-managed step in your weight loss journey.

Are you thinking of switching from Wegovy to Mounjaro? At Semapen, we offer step-by-step advice from real UK experts to help you get the most from your new medication. You can find out if you're eligible today by taking our quick digital consultation.

Sources

1. Jastreboff, A.M. et al. (2022) "Tirzepatide Once Weekly for the Treatment of Obesity" The New England Journal of Medicine, 387(3) https://doi.org/10.1056/NEJMoa2206038

2. Wilding, J.P.H. et al. (2021) "Once-Weekly Semaglutide in Adults with Overweight or Obesity" The New England Journal of Medicine, 384(11) https://doi.org/10.1056/NEJMoa2032183

3. Novo Nordisk (2026) Wegovy [patient information leaflet]. Retrieved from https://www.medicines.org.uk/emc/files/pil.13800.pdf

4. Eli Lilly and Company (2026) Mounjaro [patient information leaflet]. Retrieved from https://www.medicines.org.uk/emc/files/pil.15481.pdf

This article was reviewed and approved by Lujain Alhassan, Bariatric Nutritionist, on 3 May 2026.

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