Switching from Saxenda to Mounjaro: What Your Body May Experience

Saxenda and Mounjaro both act on GLP-1 receptors, but they are not identical medicines. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it acts on an additional pathway that Saxenda does not. Saxenda is also a daily injection, while Mounjaro is taken once weekly. Because of these differences, your body is responding to a new mechanism, a new dosing rhythm, and — especially in the early weeks — a dose that your prescriber has chosen as a starting point for you.

Commonly reported experiences when transitioning to Mounjaro include:

• Nausea — often most noticeable in the first few days after each early dose
• Changes in appetite and food noise — many people notice these feel different or more pronounced than with their previous medicine
• Gastrointestinal effects — including loose stools, constipation, indigestion, or reflux
• Fatigue or mild dizziness — sometimes reported in the adjustment period
• Injection-site reactions — redness or tenderness at the site, particularly if you are still settling into a rotation routine

These effects are not universal, and their intensity varies from person to person. For many people, they ease noticeably within the first few weeks as the body adapts. According to electronic Medicines Compendium (eMC) product information, gastrointestinal events are among the most commonly reported effects with tirzepatide, particularly during the initial period of use.

If you are also curious about switching in other directions, our guides on moving from Ozempic to Mounjaro and switching from Wegovy to Mounjaro cover those transitions in more detail. If your prescriber is considering a different path, you may also find our page on switching from Saxenda to Wegovy useful for comparison.

If any symptom is severe, persistent, or causing you concern — particularly vomiting you cannot manage, significant abdominal pain, or anything that feels unusual — contact your healthcare professional promptly rather than waiting it out.

One of the most valuable things you can do during a medicine switch is keep a clear, dated record of how you feel — and that is exactly where GLP Trackr's side-effect tracking feature comes in. Rather than trying to remember whether that nausea was worse in week one or week two, you can log each symptom as it happens, rate its intensity, and watch patterns emerge over time.

This kind of record is genuinely useful at your next prescriber appointment. Instead of a vague "I felt a bit off at the start", you can share a clear picture: which days were harder, whether symptoms followed each injection, and when things began to improve. The app's dose logging feature also means your injection dates and strengths are all in one place, so you and your prescriber can correlate how you felt with where you were in your schedule.

GLP Trackr also lets you log daily check-ins covering energy, mood, and appetite — helpful context during a transition when more than just digestion may feel different.

GLP Trackr helps you capture this so you can discuss it with your prescriber — it is not a substitute for their guidance, and any decisions about your dose or medicine remain entirely with them. Any side effect you are unsure about should be raised with your healthcare professional, and if your prescriber advises it, effects can be reported to your national reporting scheme (such as the UK's Yellow Card scheme).

For a broader overview of what people commonly experience on Mounjaro, visit our guide to Mounjaro side effects.

Want to start logging your transition from day one? GLP Trackr is free to try for 7 days — available on the App Store and Google Play. Your future self (and your prescriber) will thank you for the notes.