Switching from Mounjaro to Wegovy | A simple guide

Published on: October 9, 2025 Medically reviewed by: Dr Thush Balan

Thinking about switching from Mounjaro (tirzepatide) to Wegovy (semaglutide)? You are not alone. With recent UK price changes for Mounjaro, many patients are exploring Wegovy as a more affordable option while keeping results on track.

At HeySlim, every switch is reviewed by a UK-based doctor. We look at your current dose, any side effects, your weight loss so far, and your goals. We then confirm the safest starting dose of Wegovy for you. You will have direct access to a HeySlim weight loss doctor for questions about side effects, nutrition, exercise and staying motivated.

Quick summary

Leave a seven day gap between your last Mounjaro injection and your first Wegovy dose.
You do not always need to start from scratch. Your Wegovy starting dose is usually mapped from your current Mounjaro dose. This is a guide only and your doctor will personalise it after review.
Some pharmacy-led sites use more cautious lower starting doses. HeySlim is doctor-led and personalises your plan after medical review.
You can message your HeySlim doctor any time for side effects, nutrition and exercise help.

The difference between Mounjaro and Wegovy

Both are weekly injections that help control appetite.

Wegovy contains semaglutide.
Mounjaro contains tirzepatide.

How they work. Both medicines activate the GLP-1 receptor. GLP-1 is a natural gut hormone that tells your brain you are full and slows how quickly your stomach empties. That means smaller portions feel satisfying and you stay fuller for longer.

What makes Mounjaro different. Mounjaro is a dual agonist. It acts on two hormones: GLP-1 and GIP. Adding GIP on top of GLP-1 may give stronger appetite and metabolic effects for some people.

What results looked like in trials.

Wegovy (semaglutide): Up to about 20.7% average weight loss at the highest dose with lifestyle changes.
Mounjaro (tirzepatide): Up to about 22.5% average weight loss at the highest dose with lifestyle changes.

These are averages from clinical studies. Individual results vary. At HeySlim your plan and starting dose are doctor reviewed and personalised to you.

How the switch works at HeySlim

Step 1. Quick clinical update

Tell us your last Mounjaro dose and date. Share any side effects and your recent weight changes.

Step 2. Doctor review

A HeySlim doctor reviews your history. We consider other health conditions such as diabetes or reflux, any side effects, and your rate of weight loss. We then suggest the right Wegovy starting dose for you.

Step 3. Plan your start date

We confirm your first Wegovy injection at least seven days after your final Mounjaro dose. Keeping your usual injection day can help routine.

Step 4. Start Wegovy

Use the pen as instructed. Prime once before first use only.

Step 5. Check ins and dose progression

We monitor side effects, appetite and weight. Your doctor advises if and when to increase your dose.

What to expect in the first four to six weeks

Mild stomach symptoms are common early on. Nausea, bloating, or feeling full quickly. These usually improve after the first few weeks.
Some patients notice a brief pause in weight loss after the switch. This is usually temporary.
Lifestyle support matters. You can access your HeySlim doctor for advice on nutrition, exercise, sleep and habits that support results.

Practical tips for a smooth switch

Keep the same weekly injection day if possible.
Store Wegovy in the fridge before first use. Two to eight degrees Celsius. After opening, store in the fridge or at room temperature up to thirty degrees Celsius for up to six weeks.
Eat smaller, protein rich meals. Avoid heavy or fatty meals on injection day to reduce nausea.
Drink water and include fibre to help with constipation.

Why switch with HeySlim

Doctor reviewed plan in the UK. Not just an automatic conversion.
Direct access to your weight loss doctor for side effects and for questions about nutrition and exercise.
If you have had troublesome side effects with Mounjaro, we can start at a safer Wegovy dose and move up more gradually.
Clear check ins and a stepwise titration plan that balances comfort and results.

Frequently asked questions

Do I need to wait seven days before starting Wegovy?

Yes. A one week gap is recommended to allow Mounjaro to clear before starting Wegovy. Your doctor may advise differently in special situations.

Will I lose progress when I switch?

Most patients maintain momentum after a short transition. If you have plateaued or struggled with side effects, switching can help.

Do I have to start on the lowest Wegovy dose?

Not always. We map from your last Mounjaro dose and how well you tolerated it. Your doctor confirms the safest starting point.

Next steps

Complete the short HeySlim assessment with your last Mounjaro dose and date.
Your case is reviewed by a UK based doctor.
Your Wegovy pen is dispatched and ready to start seven days after your last Mounjaro dose.
Check in with your HeySlim doctor for dose adjustments and support.