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 And Social Impact: How It Compares To Wegovy
Weight loss medications like Mounjaro (tirzepatide) and Wegovy (semaglutide) have reshaped conversations around weight management in the UK. Both are prescription-only GLP-1-based injectables, but they work differently and may suit different people. Understanding the differences—including their mechanisms, clinical trial results, and social factors like injection frequency and cost—helps you and your GP decide which might be appropriate for you. This guide compares both medications factually, without claiming one is superior to the other.
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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.
How Mounjaro And Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist—it activates two natural hormone pathways simultaneously. This dual mechanism may help regulate appetite, reduce food cravings, and support insulin response. It's a once-weekly injection delivered via a KwikPen device.
Wegovy (semaglutide) is a single GLP-1 receptor agonist—it activates only the GLP-1 pathway. It also supports appetite reduction and fullness signals, but through one mechanism rather than two. Wegovy is also a once-weekly injection. Clinical trial data showed:
- Mounjaro (SURMOUNT-1): average 15–clinically studied weight loss at different doses
- Wegovy (STEP-1): average approximately clinically studied weight loss at the maximum dose of 2.4 mg
Both require a UK prescription following clinical assessment. Individual results vary significantly based on genetics, lifestyle, and adherence.
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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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Social And Practical Factors In Your Choice
Beyond mechanism and efficacy, practical factors matter. Both injections are once-weekly, reducing injection frequency compared to daily alternatives like Saxenda (liraglutide). Cost varies—private prescriptions typically range from £129–£320 monthly depending on dose and provider. NHS access is through specialist tier 3 weight management services, with significant waiting lists in many regions. Oral contraceptive users on Mounjaro must use additional contraception for 4 weeks after starting and after each dose increase, whereas Wegovy has no such requirement. Social stigma around injectable medications is decreasing, but some people prefer discrete options. Your GP or prescriber will assess which medication is clinically appropriate based on your health profile, eligibility, and personal circumstances—not which has better "social impact," as both support meaningful health outcomes when used alongside diet and exercise.
- 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?
Mounjaro is a dual GIP + GLP-1 agonist (two mechanisms), while Wegovy is a GLP-1 agonist only (one mechanism). Both are once-weekly injections. Clinical trials showed Mounjaro resulted in slightly higher average weight loss (15–21%) compared to Wegovy (approximately 15%), but individual results vary.
Which medication causes fewer side effects?
Both have similar common side effects: nausea, diarrhoea, vomiting, and constipation. Mounjaro users may experience more gastrointestinal effects initially due to its dual mechanism. Individual tolerance varies. Your prescriber can help manage side effects through dose adjustment or supportive measures.
Is Mounjaro or Wegovy available on the NHS in the UK?
Both are available through NHS specialist tier 3 weight management services, but access varies by region and availability is limited. Private prescriptions are available through online assessments with UK-licensed prescribers. Waiting times for NHS services can be lengthy in many areas.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching is possible but must be managed by your prescriber. There's no official conversion chart—approximate equivalence exists (e.g., Wegovy 2.4 mg ≈ Mounjaro 10–15 mg), but any switch requires medical guidance and careful dose adjustment.
Do these medications affect contraception?
Mounjaro may reduce absorption of oral contraceptives, so additional contraception (barrier method or switch) is needed for 4 weeks after starting and after each dose increase. Wegovy has no such requirement. Discuss contraception with your prescriber before starting either medication.
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