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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Mounjaro vs Wegovy — Which Is Right for You?
When choosing a weight management injection through an online clinic in the UK, understanding the differences between Mounjaro (tirzepatide) and Wegovy (semaglutide) is essential. Both are prescription-only GLP-1-based medications approved for weight management in UK adults, but they work slightly differently, have different dosing schedules, and produced different results in clinical trials. Your prescriber will assess which is more suitable for your individual circumstances following a clinical assessment. Here we compare the two to help you understand the key differences.
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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 Work Differently
The primary difference between these medications lies in their mechanism. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways in the gut and brain. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. Both slow gastric emptying and help regulate appetite, but Mounjaro's dual action on GIP and GLP-1 may support additional effects on fat utilisation and energy regulation.
Clinical trial data shows differences in average weight loss: in the SURMOUNT-1 trial, Mounjaro at 15 mg helped participants lose an average of 20.9% of body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity. In the STEP-1 trial, Wegovy at 2.4 mg resulted in an average weight loss of approximately 14.9% over 68 weeks under similar lifestyle support. Individual results vary significantly, and these are trial averages, not assured outcomes.
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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.
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Dosing, Availability, and Which Is Right for You
Dosing differences: Mounjaro starts at 2.5 mg weekly and escalates to a maximum of 15 mg. Wegovy starts at 0.25 mg and escalates to 2.4 mg. Both require a minimum of four weeks at each dose before increasing. Side effects profile is similar for both — nausea, diarrhoea, constipation, and stomach pain are common, though these typically improve over time.
Both medications are available through UK online clinics following a clinical assessment by a registered prescriber. Your prescriber will evaluate your medical history, current health conditions, BMI, and individual circumstances to determine which medication (if either) is appropriate. Some people may be prescribed one over the other based on personal factors, contraindications, or previous medication responses. Neither is universally "better" — suitability is individual.
- 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 Wegovy to Mounjaro or vice versa through an online clinic?
Yes, prescribers can manage switches between medications. However, there is no official conversion chart — switching requires prescriber guidance and new dose titration. Never attempt to convert doses yourself. Your prescriber will assess whether a switch is clinically appropriate and restart titration if needed.
Which medication causes fewer side effects — Mounjaro or Wegovy?
Both have similar side effect profiles. Nausea and gastrointestinal effects are common with both. Individual tolerance varies — some people find one more tolerable than the other. Your prescriber and personal experience over time will guide management. Most side effects improve as your body adjusts.
Are Mounjaro and Wegovy available on the NHS for online clinic access?
NHS access to both medications is through specialist tier 3 weight management services, not typically via online clinics. Private online clinics offer both following a clinical assessment and private prescription. NHS availability varies significantly by region and waiting lists can be lengthy.
How long does each medication take to show weight loss results?
Weight loss typically becomes noticeable after 4–8 weeks, with most significant loss occurring over 16–24 weeks. Both medications require consistent use alongside dietary changes and physical activity. Results continue to improve with proper dose titration and lifestyle support over several months.
What happens if I stop taking Mounjaro or Wegovy?
Weight loss effects typically plateau and may reverse if the medication is stopped and lifestyle changes are not maintained. These are weight management tools, not permanent solutions. Ongoing use, combined with sustained dietary and activity habits, supports long-term weight management.
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.