Switching from Wegovy to Mounjaro Side Effects
Side Effects and What to Expect
- Some patients experience fewer side effects switching due to prior GLP-1 exposure.
- Side effects may peak within 24-72 hours, improving over 1-2 weeks.
- Anti-nausea medication can help manage symptoms.
- Constipation and diarrhea are common but usually manageable.
- Gradual dose escalation reduces risk of severe side effects.
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Switching From Wegovy to Mounjaro Side Effects: What to Expect
You've finally made the decision to switch from Wegovy to Mounjaro. The clinical trial data looks promising, your provider has approved the transition, and you're ready for better results. But there's one thing nagging at you: what's going to happen when you start the new medication?
The nausea you experienced when starting Wegovy wasn't exactly pleasant. Neither was the first month of digestive issues. Now you're wondering if you'll have to go through all that again with Mounjaro, or whether it might be even worse.
Here's the reassuring truth: most patients who tolerated Wegovy well find the transition to Mounjaro manageable. Yes, you may experience some side effects, but they're typically similar to what you've already been through. And with proper preparation, you can minimise their impact on your daily life.
For detailed guidance on switching providers and what to expect throughout the process, see our complete guide to swapping Mounjaro providers in the UK.
What Side Effects Can You Expect When Switching to Mounjaro?
Mounjaro and Wegovy share very similar side effect profiles. Both medications work on the GLP-1 pathway, so your body has already adapted to many of the mechanisms that cause digestive side effects. This prior exposure often means the transition is smoother than starting from scratch.
That said, Mounjaro also activates GIP receptors, which Wegovy doesn't. This dual action is why it's more effective for weight loss, but it can also mean slightly different side effects for some patients.
Clinical trial data for tirzepatide (Mounjaro) shows:
- Nausea: Up to 18-29% of patients (varies by dose and indication)
- Diarrhoea: 13-23% of patients
- Constipation: Up to 9% of patients
- Vomiting: 6-14% of patients
- Decreased appetite: Up to 10% of patients (though this is often the intended effect)
- Dyspepsia (indigestion): Up to 9% of patients
These percentages are broadly comparable to Wegovy's side effect profile. In the SURPASS-2 trial, which directly compared tirzepatide and semaglutide, the most common adverse events were gastrointestinal and described as mild to moderate in severity in both groups.
Will Mounjaro Side Effects Be Worse Than Wegovy?
This is the question that worries most patients considering the switch. The honest answer: it varies from person to person, but there's reason for optimism.
Because your body has already adapted to a GLP-1 medication, you've essentially done the hard work. The receptors that caused nausea when you first started Wegovy have already adjusted. When you switch to Mounjaro, you're not starting from zero.
Some patients actually report fewer side effects after switching. One UK provider notes that patients sometimes find Mounjaro easier to tolerate than Wegovy, while others experience the opposite. There's no way to predict which group you'll fall into until you try.
What we do know from clinical trials:
- Side effects are dose-dependent. Higher doses cause more GI symptoms.
- Most side effects occur during dose escalation, not at maintenance doses
- Side effects are typically transient and improve as your body adjusts
- Long-acting GLP-1 medications (like both Wegovy and Mounjaro) tend to cause less nausea but more diarrhoea than short-acting options
When Will Side Effects Hit After Switching?
Understanding the timeline helps you prepare. Side effects from Mounjaro typically follow a predictable pattern:
First 24-72 Hours After Injection:
Peak drug concentration occurs 8-72 hours after injection. If you're going to feel nauseous, this is usually when it happens. Many patients report that side effects hit hardest on day 2 or 3 after their injection.
First 1-2 Weeks:
Your body is adjusting to the new medication. Side effects may be more noticeable than they will be later. This is normal and doesn't mean Mounjaro isn't working for you.
Weeks 2-4:
Most patients notice side effects beginning to settle. Your digestive system is adapting to the medication's effects on gastric emptying.
Dose Escalation Periods:
Each time your dose increases, you may experience a temporary return of side effects. This typically improves within 1-2 weeks at the new dose.
How to Minimise Side Effects When Switching
You've been through GLP-1 treatment before, so many of these strategies will be familiar. Apply what you learned during your Wegovy journey:
💡 Key Strategies:
- Eat smaller, more frequent meals: Both medications slow gastric emptying. Large meals sit in your stomach longer and are more likely to cause nausea. Stick to portions that worked well on Wegovy.
- Avoid trigger foods: Fatty, fried, and spicy foods tend to worsen nausea. If certain foods caused problems on Wegovy, they'll likely cause problems on Mounjaro too.
- Stay hydrated: Dehydration worsens nausea and can lead to more serious complications if vomiting or diarrhoea occur. Sip water throughout the day rather than drinking large amounts at once.
- Time your injection strategically: Some patients find side effects more manageable if they inject on a day when they can rest. If you know day 2 tends to be rough, plan accordingly.
- Start at an appropriate dose: Working with an experienced provider who considers your Wegovy history can help you start at a dose that balances effectiveness with tolerability.
When Side Effects Need Medical Attention
Most side effects are uncomfortable but not dangerous. However, some symptoms require prompt medical attention:
⚠️ Seek Medical Attention For:
- Severe or persistent abdominal pain (could indicate pancreatitis)
- Vomiting that won't stop or prevents you from keeping fluids down
- Signs of dehydration: dizziness, dark urine, extreme thirst, infrequent urination
- Severe allergic reaction: difficulty breathing, swelling of face/lips/tongue, severe rash
- Vision changes (particularly important if you have diabetes)
- Signs of gallbladder problems: pain in upper right abdomen, fever, jaundice
If you experience any of these symptoms, contact your healthcare provider or seek medical attention immediately.
Are There Side Effects Specific to Switching Medications?
Good news here: there are no specific side effects caused by switching from Wegovy to Mounjaro, provided you follow proper switching guidance (including the 7-day washout period between your last Wegovy dose and first Mounjaro dose).
The side effects you experience will be Mounjaro's standard side effects, not special "switching" side effects. If you skip the washout period and take both medications too close together, you significantly increase your risk of severe GI symptoms due to receptor overstimulation.
During the 7-day gap itself, most patients notice very little change. Wegovy stays active in your system for several days after your last injection, so you won't suddenly feel dramatically different.
What If Mounjaro Side Effects Are Unbearable?
Sometimes the switch doesn't go as smoothly as hoped. If you're struggling with side effects, you have options:
🔄 Available Options:
- Dose reduction: Your provider may recommend dropping back to a lower dose temporarily
- Slower titration: Staying at your current dose longer before increasing
- Anti-nausea medication: Short-term use of prescription anti-emetics can help you through the adjustment period
- Switching back: If Mounjaro truly doesn't agree with you, returning to Wegovy (or trying a different medication) is always an option
The key is communicating with your provider rather than suffering in silence or abandoning treatment altogether.
Managing Side Effects With G-1 Nutrition's Support
Side effect management is where provider quality really matters. Some clinics hand you a prescription and disappear. When nausea hits at 10pm on a Saturday, you're left searching forums for advice.
G-1 Nutrition takes a different approach:
- Individualised starting doses based on your Wegovy history and tolerance
- Responsive clinical support from GPhC-registered pharmacists who understand these medications
- Guidance on managing side effects tailored to your specific situation
- Dose adjustment recommendations when needed, not just a rigid protocol
- Transparent pricing so you know exactly what you're paying
Ready to Switch with Confidence?
Complete our online assessment to discuss switching from Wegovy to Mounjaro with clinical support that doesn't disappear when things get difficult.
