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: Cost, Effectiveness, and Which Suits You
If you're looking for affordable weight loss injections in the UK, you'll likely compare Mounjaro and Wegovy. Both are prescription-only GLP-1 medications approved for weight management, but they differ in mechanism, dosing, cost, and clinical effectiveness. Understanding these differences helps you and your GP or prescriber decide which option may be right for you. This guide breaks down the facts so you can make an informed choice based on your health needs and budget.
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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.
Mounjaro vs Wegovy: Clinical Evidence and How They Work
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two different hormone pathways to help regulate appetite and blood sugar. In the SURMOUNT-1 clinical trial, participants taking Mounjaro 15mg lost an average of 20.9% of their body weight over 72 weeks alongside a reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a GLP-1 receptor agonist only — activating a single hormone pathway. In the STEP-1 trial, participants taking Wegovy 2.4mg lost an average of 14.9% of body weight over 68 weeks under similar conditions.
The key difference: Mounjaro's dual mechanism may result in greater average weight loss, though individual results vary significantly. Both require clinical assessment and a prescription. Neither assures specific outcomes, and both work best alongside lifestyle changes rather than as standalone treatments.
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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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Cost, Dosing, and UK Eligibility — What You Need to Know
Both Mounjaro and Wegovy are available through NHS specialist weight management services (subject to regional availability and waiting lists) or through private prescribing. Private costs vary by dose and provider, but generally range from £129–£320 per month. Mounjaro typically costs slightly more due to its dual mechanism and higher maximum dose (15mg vs Wegovy's 2.4mg maximum). Eligibility for both medications is the same: BMI 30 or above, or BMI 27–29.9 with weight-related health conditions. Use our free BMI calculator to check your personal BMI, and our GLP-1 weight loss calculator to estimate potential outcomes at different doses. Your prescriber will assess which medication is more suitable for your individual circumstances, medical history, and budget.
- 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.
Is Mounjaro cheaper than Wegovy in the UK?
Mounjaro and Wegovy costs are similar, but Mounjaro is often slightly more expensive due to its dual mechanism. Both range from approximately £129–£320 per month depending on dose and provider. NHS costs are the same regardless of which you receive. Compare prices with your prescriber or pharmacy to find the most affordable option for your situation.
Which causes more weight loss — Mounjaro or Wegovy?
Clinical trials show Mounjaro users lost approximately 20.9% of body weight on average, versus 14.9% for Wegovy. However, individual results vary significantly based on genetics, diet, exercise, and consistency. Neither assures specific outcomes. Your prescriber will recommend based on your health profile, not just trial averages.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but requires prescriber guidance. There is no official conversion chart — the doses are not directly equivalent. Your prescriber will manage the switch carefully to minimise side effects and maintain effectiveness. This should only be done under medical supervision.
Which injection is easier to use — Mounjaro or Wegovy?
Both are once-weekly injections in a pre-filled pen. Mounjaro uses a KwikPen, Wegovy uses an auto-injection pen. Both are administered subcutaneously (under the skin) and can be self-injected. Ease of use is similar; personal preference varies. Your prescriber can show you both devices.
How long does it take to see weight loss results with these injections?
Weight loss typically begins within 2–4 weeks on Mounjaro or Wegovy, but most significant results occur after 12–16 weeks as doses increase. Both medications work best alongside a reduced-calorie diet and increased physical activity. Track your progress with our free progress tracker to monitor changes over time.
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.