How Long to Wait When Switching from Mounjaro to Wegovy?

Mounjaro (tirzepatide) is an effective weekly injection used for losing weight and long-term weight management.

However it’s not suitable for everyone. And some patients are concerned about recent changes to the price of Mounjaro in the UK. If this is the case, you might be considering switching from Mounjaro to Wegovy, another weight loss treatment.

But how long do you need to wait before starting it?

This article explains how long to wait before switching and why a short pause matters. We’ll also explain what a “washout period” is, what a typical switch looks like, and how to switch safely with a clinician.

Why Waiting to Switch Matters

Waiting when switching from Mounjaro to Wegovy matters because both medications work in similar ways. Taking them together can be harmful.

Both are weight loss injections known as glucagon-like peptide 1 (GLP-1) receptor agonists. Their active ingredients mimic a gut hormone called GLP-1, which suppresses hunger and slows stomach emptying.

While this action helps you eat less, it also comes with potential side effects like nausea, vomiting and diarrhoea. These are common ones on both medications. Using them at the same time can increase your risk of side effects, including serious ones.

The Risks of Switching Without a Break

If you don’t take a break between treatments, you could risk:

• Worse (and Serious) Side Effects: Overlap can mean extra nausea, vomiting, diarrhoea, tummy cramps and poor appetite. Both weight loss medications slow stomach emptying. If sickness is bad, dehydration can follow.
  
• Dose Confusion: If both drugs are still active, it’s hard to know which one is causing a problem. That makes it tougher to choose the right dose next time.
  
• Goes Against Label Advice: Official guidance for semaglutide (the active ingredient in Wegovy) says not to use it with other GLP-1 medicines. Tirzepatide (the active ingredient in Mounjaro) acts on the GLP-1 pathway too, so clinicians don’t advise using them together.

What is the Washout Period for Mounjaro?

When moving from Mounjaro to Wegovy, the washout period is one week (seven days).

A washout period is a planned gap between stopping one medicine and starting the next. It allows time for levels of the first drug to decrease.

So, if you’re wondering “can you take Wegovy a week after Mounjaro?” The answer is yes. Leave at least seven full days after you stop taking Mounjaro before you take your first Wegovy dose. This short break lowers the chance of extra side effects and keeps dosing simple.

Typical Switching Timeline

Here’s how the seven-day washout usually works in practice:

• To Inject on the Same Day: If your last Mounjaro dose is on Friday, take your first Wegovy dose on the next Friday (seven days later).
• To Change Your Injection Day: If your last Mounjaro was on Friday and you prefer Monday for future doses, you can start Wegovy on the Monday after next. That’s a 10-day gap.

You may not need to go back to the lowest dose. The best starting dose depends on your current Mounjaro dose and how you’ve tolerated treatment. For example if you were just starting Mounjaro, you would likely use the lowest dose of Wegovy.

Switching With Medical Supervision

“If you decide to switch to Wegovy, it’s straightforward,” Abdal Alvi, Chief Clinical Officer at Simple, explains. “We can suggest a safe dose for you to switch to so you won’t need to restart your treatment from the beginning.”

You’ll just need to follow these steps:

1. Fill in an Assessment Online: Your prescriber will review your medical history and body weight to assess suitability and keep you safe. Tell us your current Mounjaro dose and the date of your last injection. We’ll set your Wegovy start date at least seven days later.
   
2. Choose a Starting Wegovy Dose: Your provider will guide you on the safest and most appropriate dose. If you’re worried about side effects, you can choose to start on a lower dose.
   
3. Pick Your Weekly Day: Keep the same day each week so it’s easy to remember. This will help you follow your dosing schedule correctly.
   
4. Know What to Expect: Common side effects include nausea, vomiting, diarrhoea and constipation. If you can’t keep fluids down, have severe tummy pain or feel unwell, get medical help.

“You’ll also be giving important information about switching within the assessment. Please read this very carefully,” Abdal stresses.

Our clinical team is here for you throughout your weight loss journey. So if you need any support, call us on 0141 774 5023.

Key Takeaways

• Wait One Week: Leave seven days after stopping Mounjaro and your first Wegovy dose. Do not use them together.
  
• Why the Gap Matters: Both last a long time in the body and work on similar pathways. Overlapping them can increase side effects.
  
• Plan the Switch: Plan ahead for a safe switch so you can stay on track with your long-term health. Set a start date at least seven days later and pick your weekly day. Agree on a starting Wegovy dose with your clinician.
  
• Worried About Side Effects? You don’t have to start on the higher dose. You can start on a lower Wegovy dose and build up. This can reduce the risk of side effects.
  
• Tell Your Clinician About Your Health History: Fill in your assessment honestly. Tell them about your current medications and give accurate information. This will keep you safe.

References

Almandoz, J.P., Lingvay, I., Morales, J. & Campos, C., 2020. Switching between glucagon-like peptide-1 receptor agonists: rationale and practical guidance. Clinical Diabetes [online]. 38(4), pp.390–402. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7566932/ (Accessed: 9 September 2025).

Novo Nordisk A/S, 2025. WEGOVY (semaglutide) injection: Highlights of prescribing information [PDF online]. U.S. Food and Drug Administration. Revised: August 2025. Available from: https://www.accessdata.fda.gov/drugsatfda_docs/label/2025/215256s024lbl.pdf (Accessed: 9 September 2025).

Authorship

Authored by Hannah Morgan

Content Writer
Hannah Morgan is a content writer at Simple Online Pharmacy. She started her career as a health, fitness and scientific writer and researcher in 2022, alongside a degree in Biomedical Science. She has since worked as a content writer for various companies, brands and a well-known YouTuber. Hannah’s main goal is to provide scientifically-backed and engaging content.

Medically Reviewed by Richard Wood

Pharmacist / Clinical Specialist
GPhC reg: 2078802
Richard is a pharmacist and content reviewer at Simple Online Pharmacy. He officially joined the team in 2024 after several years of working with the company as a contractor. Prior to that, he spent over 11 years as a community pharmacist, building a strong foundation in patient care.