Switching between GLP-1 medications has become increasingly common in the UK, particularly since the Mounjaro price increase in September 2025 prompted many patients to evaluate whether Wegovy might offer better value. Here's what you need to know about making the transition safely.
Why people switch
The most common reasons include:
- Cost: Price changes can make one medication significantly cheaper than the other at certain doses
- Side effects: Some people tolerate one medication better than the other. Nausea rates differ (higher with Wegovy in trials, lower with Mounjaro)
- Effectiveness plateau: Some people stop losing weight on one medication and find the other restarts progress
- Cardiovascular benefit: Patients with heart disease may want Wegovy specifically for its proven cardiovascular protection from the SELECT trial
- Supply issues: Occasional stock shortages can force a temporary or permanent switch
- Clinical recommendation: A prescriber may recommend switching based on individual response
The critical rule: never take both simultaneously
Mounjaro and Wegovy must not be taken at the same time. Both act on GLP-1 receptors, and combining them can cause severe gastrointestinal side effects, dangerous drops in blood sugar, and other serious complications. Always stop one before starting the other.12
How to switch safely
The standard approach is:
- Take your last injection of your current medication on your usual day
- Wait at least 1 week (until your next scheduled injection day)
- Start the new medication on that next injection day, at the dose your prescriber recommends
Your prescriber will determine the appropriate starting dose of the new medication. In some cases, you may be started at a mid-range dose (rather than the very first titration dose) to avoid losing momentum. In other cases, particularly if you experienced side effects on your previous medication, you may restart from a lower dose and re-titrate.
Will I regain weight during the switch?
A one-week gap between medications is unlikely to cause meaningful weight regain. GLP-1 medications have long half-lives, so their effects persist for several days after the last injection. Most people don't notice any change in appetite or weight during a standard one-week transition.
If the switch involves re-titrating from a lower dose, you may experience slightly reduced appetite suppression during the escalation period. Maintaining your dietary habits during this time helps ensure continuity.
Switching from Wegovy to Mounjaro
If you're moving from semaglutide (Wegovy) to tirzepatide (Mounjaro), your prescriber will likely start you on a dose that's clinically appropriate based on where you were on Wegovy. There's no exact dose equivalence between the two medications (they're different drugs acting on different receptor profiles), so the starting dose is a clinical judgement.
Switching from Mounjaro to Wegovy
The same principle applies in reverse. Several UK providers have developed specific switching protocols — for example, some use a 7-day clinical switching process. Your prescriber will advise on the right Wegovy starting dose based on your Mounjaro dose, tolerability history, and weight loss goals.2
The key message
Switching is safe and straightforward when done under clinical supervision. Never switch on your own, never take both medications simultaneously, and always follow your prescriber's dose recommendations for the new medication. Most people make the transition smoothly and continue losing weight or maintaining their progress.