Switching between weight loss medications is sometimes necessary. You may need to change if you are experiencing side effects, your weight has plateaued or you simply want to try other options. In all cases your pharmacist or doctor will decide if switching is a suitable choice.
It’s usually a requirement to wait at least seven daysbetween your last dose of Mounjaro and your first dose of Wegovy, or five weeks between your final dose of Wegovy and your first dose of Mounjaro. You may also need to adjust your dosage to begin with. Other than that, you shouldn’t have to change your routine too much.
Both Wegovy and Mounjaro are weekly injections but they work in slightly different ways. So, in this guide, we explain how switching works and what to expect.
How these treatments work
Wegovy contains semaglutide, a GLP-1 receptor agonist. GLP-1 is a natural hormone that helps regulate appetite and blood sugar. By mimicking this hormone, Wegovy helps you feel fuller for longer which can reduce cravings and support gradual weight loss.
Mounjaro contains tirzepatide, which is a dual agonist. It activates GLP-1 receptors -just like Wegovy – but also GIP receptors. This dual action can have an even greater impact on blood sugar regulation and appetite control.
Some people find they respond better to Mounjaro while others prefer Wegovy.
Eligibility for switching
The eligibility criteria for Wegovy is broadly the same as it is for Mounjaro. Most people need to have:
- A BMI of 30 or above, or
- A BMI of 27 or above with weight-related health conditions such as type 2 diabetes, high blood pressure or cardiovascular disease
If your BMI falls below the eligibility threshold during treatment, you may no longer meet the eligibility criteria. Your prescriber will review your progress and decide whether switching is a suitable option for you in your specific circumstances
Switching from Mounjaro to Wegovy
If you’re switching from Mounjaro to Wegovy, you should wait seven days after your last Mounjaro injection before taking your first injection of Wegovy.
Your first Wegovy dose will depend on how much your final Mounjaro dose was. For example:
| Mounjaro final dose | Wegovy first dose |
| 2.5mg | 0.5mg |
| 5mg | 0.5mg |
| 7.5mg | 0.5mg |
| 10mg | 1mg |
| 12.5mg | 1mg |
| 15mg | 1mg |
Your prescriber may adjust the starting dose depending on your previous progress and how well you tolerated Mounjaro.
Switching from Wegovy to Mounjaro
If you’re switching from Wegovy to Mounjaro, you should wait five weeks after your last Wegovy injection before taking your first dose of Mounjaro.
This longer waiting period is needed because Wegovy has a long half-life and can remain active in your body for several weeks after a final dose.
No matter what dose of Wegovy you were taking, you should always start on the 2.5mg dose of Mounjaro.
Step-by-step switching process
Switching is straightforward, here’s how to do it in six simple steps:
- Consultation – your prescriber will review your medical history, BMI and treatment response
- Approval – if switching is suitable, they will issue you with a prescription
- Last dose – take the final dose of your current medication
- Waiting period – follow the guidance: wait one week if you’re switching from Mounjaro to Wegovy or five weeks for Wegovy to Mounjaro
- Start new treatment – begin injections at the recommended starting dose
- Monitor and review – attend follow-ups where required and continue your weight loss journey
Are there any differences you should know about?
Although Wegovy and Mounjaro are both weekly injections, there are a few practical differences to keep in mind.
Wegovy pens only need to be primed before the very first use, whereas Mounjaro pens must be primed before every injection.
Both medicines need to be stored in the fridge, but if you are travelling or need to keep them at room temperature, then Wegovy can remain stable for up to 42 days compared with 30 days for Mounjaro.
These differences may influence which treatment you find easier to use and could play a part in your decision to switch.
Why you might switch
There are several reasons why people move from one weight-loss medication to another. Popular reasons include:
- Side effects – if one drug causes significant nausea, constipation or other problems then you might want to try another
- Cost or availability – sometimes one treatment is easier to access or cheaper to buy
- Plateau – in cases where weight loss has slowed down despite continued use a different treatment could work better
- Health benefits – Wegovy has proven cardiovascular protection, reducing the risk of stroke or heart attack. Mounjaro has shown similar results too, but it’s not specifically licensed for it
Side effects of switching
Most people tolerate Wegovy and Mounjaro well, but it’s normal to experience some side effects when starting or switching between them.
Some of the more common side effects include:
- Nausea
- Constipation
- Diarrhoea
- Decreased appetite
- Indigestion and acid reflux
- Stomach pain
These side effects tend to improve as your body adjusts to the medication.
More serious reactions such as pancreatitis or gallbladder problems are rare but require urgent medical attention if they do occur. If you’re concerned about how you’re feeling you should speak to your pharmacist or doctor.
Is it safe to switch?
Switching between Wegovy and Mounjaro is typically safe when it’s done under medical supervision. Your prescriber will consider your medical history, current dose and any side effects you’ve experienced before deciding the right time and starting dose for your new treatment.
Manufacturers sometimes advise longer periods for your body to washout previous medication from your system. But in practice, shorter intervals are often used because they are still safe and help you avoid unnecessary breaks in your treatment.
This approach allows you to maintain momentum in your weight-loss journey while your prescriber closely monitors how you respond to the new medication.
Benefits of each medication
Wegovy
Proven to reduce the risk of heart attack and stroke alongside significant weight-loss results. Wegovy also doesn’t affect oral contraceptives. However, as with any new medication, you should let your prescriber know about all other medicines you’re taking before switching.
Mounjaro
Trial data shows slightly stronger results for weight loss, with some people losing over 20% of their starting body weight.
Both medications work best when combined with a healthy diet and regular physical activity.
FAQs
Can I switch back if the new treatment doesn’t suit me?
Yes, if you experience side effects or don’t see progress then your prescriber may recommend switching back or trying an alternative.
Will I gain weight during the switch?
Weight gain is unlikely, as the effects of these medications overlap. If you continue with a healthy lifestyle and follow your prescriber’s advice, your progress should remain steady.
Is there withdrawal when stopping?
There are no withdrawal symptoms, but your appetite may increase once the medication wears off.
Is it considered safe to switch between Wegovy and Mounjaro?
Yes. Switching between Wegovy and Mounjaro is considered safe when it’s done under medical supervision. Your prescriber will guide you on the correct waiting period between treatments and choose the most suitable starting dose to reduce the risk of side effects. The overlap in how these medicines work also means there is no sudden loss of effect while changing so long as you follow the schedule advised by your clinician.
Do I need to change my diet during the switch?
No special changes are required but sticking to a balanced diet can help minimise digestive side effects.
How soon will I see results?
Some people notice changes in appetite within weeks but weight loss is gradual. Your prescriber will monitor your progress at follow-ups.
Professional support
Switching treatments should always be done with medical guidance. At myBMI, our team will:
- Review your eligibility and medical history
- Support you through the switching process
- Help you manage side effects
- Monitor your long-term progress
If you would like to learn more about how Mounjaro and Wegovy compare, read our detailed Mounjaro vs. Wegovy guide.
