The UK's most complete GLP-1 guide
Every Question Answered. Every Side Effect Explained.
- How GLP-1 medications work
- Mounjaro vs Wegovy compared
- Injection instructions
- Side effects & solutions
- What to eat on treatment
- FAQs answered
Free tracker included with every download this week
Switching to Wegovy From Mounjaro — What You Need to Know
If you're considering switching from Mounjaro to Wegovy, or your prescriber has suggested a change, it's important to understand how these two weight loss injections differ and why the switch might be recommended for your individual circumstances. Both are prescription-only medications used for weight management in the UK, but they work slightly differently and have different dosing schedules. This guide explains the key differences and what to expect during a medication switch.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
What Is BMI and Why Does It Matter?
Body Mass Index (BMI) is the most widely used screening tool for assessing whether your weight falls within a healthy range. Used by the NHS, GPs, and weight management services across the UK, BMI provides a quick snapshot of your weight relative to your height. The formula is simple: your weight in kilograms divided by your height in metres squared (kg/m²).
While BMI isn't a perfect measure — it doesn't account for muscle mass, bone density, or fat distribution — it remains the standard first step in identifying potential weight-related health risks including type 2 diabetes, cardiovascular disease, high blood pressure, and certain cancers.
The NHS also recommends adjusted thresholds for people of South Asian, Chinese, or Black African heritage — a BMI of 23 or above is classified as overweight, and 27.5 as obese. Our calculator includes this adjustment as a one-click toggle.
How Mounjaro and Wegovy Differ in Mechanism and Dosing
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways in the body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single hormone pathway. In clinical trials, Mounjaro showed average weight loss of approximately 15–21% of body weight (SURMOUNT-1 trial), whilst Wegovy showed approximately 15% average weight loss (STEP-1 trial), though individual results vary significantly.
Dosing also differs: Mounjaro starts at 2.5 mg weekly and escalates to a maximum of 15 mg weekly. Wegovy starts at 0.25 mg weekly and escalates to a maximum of 2.4 mg weekly. Because of these differences, approximate dose equivalences exist—for example, Mounjaro 15 mg is roughly equivalent to Wegovy 2.4 mg—but any medication switch must be managed by your prescriber, not self-managed.
Use our GLP-1 weight loss calculator to explore potential outcomes and dose comparisons between these medications.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
How It Works
Three simple steps to understand your weight and take action.
Enter your height and weight in our free calculator. Get your BMI, NHS category, healthy weight range, and ethnicity-adjusted thresholds instantly.
If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
Use our progress tracker to log your weight weekly, visualise your journey with charts, and stay motivated — all stored privately in your browser.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Why Might Your Prescriber Recommend Switching?
Reasons for switching from Mounjaro to Wegovy include side effect tolerability, individual response, cost, or availability. If you're experiencing persistent nausea, gastrointestinal upset, or injection site reactions on Mounjaro, Wegovy may be better tolerated. Conversely, if Wegovy hasn't produced adequate weight loss, your prescriber might recommend Mounjaro's dual mechanism.
Any switch requires a clinical assessment—your prescriber will not simply replace one with the other. There may be a gap between stopping Mounjaro and starting Wegovy to allow your body to adjust. Never attempt to switch medications without guidance. Both remain prescription-only medicines requiring ongoing prescriber oversight. Your GP or the prescriber managing your weight loss can discuss whether a switch is appropriate for your health profile, current weight loss progress, and any side effects you're experiencing.
- Dual GIP/GLP-1 receptor agonist
- Up to 22.5% body weight loss (SURMOUNT-1)
- Weekly injection, dose escalation over 20+ weeks
- Available via private prescription in the UK
- Doses: 2.5mg → 5mg → 7.5mg → 10mg → 12.5mg → 15mg
- GLP-1 receptor agonist
- Up to 15–17% body weight loss (STEP trials)
- Weekly injection, 5-step dose escalation
- NHS & private prescription available
- Doses: 0.25mg → 0.5mg → 1mg → 1.7mg → 2.4mg
Mounjaro vs Wegovy: Head-to-Head
A side-by-side comparison of the two most popular GLP-1 weight loss medications available in the UK.
| Feature | Mounjaro | Wegovy |
|---|---|---|
| Drug class | Dual GIP/GLP-1 agonist | GLP-1 agonist |
| Active ingredient | Tirzepatide | Semaglutide |
| Avg. weight loss | 15–22.5% | 12–17% |
| Key trial | SURMOUNT-1 (2022) | STEP 1 (2021) |
| Max dose | 15 mg weekly | 2.4 mg weekly |
| Escalation period | 20–32 weeks | 16–20 weeks |
| Administration | Weekly injection (pen) | Weekly injection (pen) |
| NHS availability | Private prescription only | NHS & private |
| Approx. private cost | £150–£250/month | £150–£300/month |
| Common side effects | Nausea, diarrhoea, constipation | Nausea, vomiting, diarrhoea |
Data sourced from SURMOUNT-1 and STEP 1 clinical trials. Costs are approximate and vary by provider. Always consult a prescriber.
Am I Eligible for Weight Loss Medication?
In the UK, eligibility for GLP-1 weight loss medications like Mounjaro and Wegovy is based on your BMI and overall health profile.
- BMI of 30 or above (obese)
- Age 18 or over
- No contraindicated conditions
- Committed to lifestyle changes
- BMI of 27 or above
- Plus type 2 diabetes
- Or high blood pressure
- Or obstructive sleep apnoea
Use our BMI calculator to check whether your BMI falls within the eligible range.
How We Built These Tools
Every calculator and guide on myweightcheck is built with accuracy and transparency in mind. Our BMI calculator uses the standard WHO formula with NHS-aligned category thresholds. Our GLP-1 projections are modelled on published clinical trial data from SURMOUNT and STEP studies.
All data stays on your device. We don't require sign-ups, and we don't store your health information on any server. Your progress tracker saves data locally in your browser using localStorage, so only you can see it.
We're based in the UK and our tools are designed specifically for UK users — supporting stone & lbs by default, referencing NHS guidelines, using NICE-approved medication data, and linking to GPhC-registered pharmacies.
Frequently Asked Questions
Common questions about BMI, weight loss medications, and our free UK tools.
Can I switch from Mounjaro to Wegovy immediately, or is there a gap?
There is typically a gap between stopping Mounjaro and starting Wegovy to allow your body to adjust. Your prescriber will advise on timing. Mounjaro takes approximately 4 weeks to fully leave your system, so Wegovy is usually started after this period. Never attempt to overlap the two medications without explicit prescriber guidance.
Will I need to restart at a lower dose of Wegovy if I switch from Mounjaro?
Yes, you will typically restart Wegovy at its standard starting dose of 0.25 mg, not jump directly to a higher equivalent dose. This allows your body to adjust to the single GLP-1 mechanism and helps your prescriber monitor tolerability. Dose escalation follows the standard Wegovy schedule from there.
Is Wegovy less effective than Mounjaro?
Clinical trials show similar average weight loss outcomes—both approximately 15% body weight on average—but individual results vary. Wegovy may be equally effective for some people; others respond better to Mounjaro's dual mechanism. Effectiveness depends on your individual physiology, adherence, and lifestyle factors, not on the medication alone.
What if I have side effects on Wegovy after switching from Mounjaro?
Some people tolerate Wegovy better than Mounjaro, and vice versa. If you experience side effects on Wegovy, inform your prescriber. They may recommend dose adjustment, slower escalation, or potentially switching back to Mounjaro or exploring another option. Never stop abruptly without prescriber guidance.
How do I know if switching is right for me?
Your prescriber will assess whether switching is appropriate based on your weight loss progress, side effects, health conditions, cost, and availability. Use our BMI calculator to track your current status, and discuss your concerns openly with your GP or prescriber managing your weight loss treatment. Switching decisions are personalised, not one-size-fits-all.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.