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
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Long-Term Effects: Mounjaro vs Wegovy
Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections used in the UK, but they work differently and have distinct long-term effect profiles. This guide compares the evidence from clinical trials and explains how their mechanisms differ. Both medications require a clinical assessment and are prescribed alongside reduced-calorie diet and increased physical activity. Understanding the differences helps your prescriber decide which option may be most suitable for your individual health needs.
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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.
Clinical Trial Evidence and Long-Term Effectiveness
Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two separate hormone pathways, which may explain its higher average weight loss in trials. The SURMOUNT-1 clinical trial showed Mounjaro at 15 mg (maximum dose) produced approximately clinically studied weight loss over 72 weeks. Wegovy, a GLP-1 agonist only, showed approximately 14.9% average body weight loss in the STEP-1 trial over 68 weeks at the maximum 2.4 mg dose.
- Mounjaro mechanism: Activates both GIP and GLP-1 pathways, affecting appetite, satiety, and glucose metabolism
- Wegovy mechanism: Activates GLP-1 pathway only, primarily affecting appetite and gastric emptying
- Long-term sustainability: Both require ongoing injection to maintain weight loss — stopping either medication typically results in weight regain over time
- Individual variation: Clinical trial averages mask significant individual variation — some people lose more, some less, and results depend on adherence to lifestyle changes
The difference in mechanisms means long-term metabolic effects may differ, though both have been studied for up to 2 years in extended trials with generally sustained benefits.
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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.
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Choosing Between Them: Individual Suitability
Neither medication is inherently "better" — your prescriber will assess which suits your individual health, medical history, and response to the tirzepatide dosing schedule. Mounjaro's dose titration (starting at 2.5 mg and escalating weekly) may take longer to reach maximum effect but allows adjustment based on side effects. Wegovy's dose escalation (starting at 0.25 mg) is also gradual but reaches 2.4 mg more quickly. Both are prescription-only in the UK, available through NHS specialist services or private clinical assessment. Your GP or prescriber can assess eligibility based on your BMI and health conditions. Use our free GLP-1 weight loss calculator to estimate potential outcomes, and our BMI calculator to understand your current health category before your consultation.
- 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.
What's the main difference between Mounjaro and Wegovy for long-term weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. SURMOUNT trials showed Mounjaro produced approximately 20.9% average weight loss versus STEP trials showing Wegovy at 14.9%. Both require ongoing use to maintain results.
How long do the effects of Mounjaro last after stopping treatment?
Weight loss from Mounjaro is typically maintained only while taking the medication. When stopped, weight regain is common over subsequent months. Long-term sustainability requires continuing the injection as prescribed by your GP or specialist.
Are there differences in long-term side effects between Mounjaro and Wegovy?
Both share similar common side effects (nausea, diarrhoea, constipation) but Mounjaro's dual mechanism may affect side effect profiles differently in individual cases. Long-term safety data up to 2 years shows both are generally well-tolerated, though individual experiences vary significantly.
Which medication is more suitable for long-term use in the UK?
There's no one-size-fits-all answer — suitability depends on your medical history, BMI, comorbidities, and individual response. Both are prescription-only and require assessment by your GP or a UK-licensed prescriber. Your healthcare professional will recommend the most appropriate option for your circumstances.
How can I track my progress with either Mounjaro or Wegovy?
Monitor your weight loss using our free progress tracker, which helps record weight changes over time. Combined with regular check-ins with your prescriber and use of our GLP-1 weight loss calculator to track estimated outcomes, this provides a comprehensive view of your long-term progress.
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.