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 Cons vs Wegovy — What You Need to Know
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight loss injections licensed in the UK, but they work differently and carry different considerations. This guide compares the drawbacks and limitations of both medications to help you understand what your prescriber might discuss during your clinical assessment. Neither medication is universally "better" — suitability depends entirely on your individual health, medical history, and lifestyle. Use our GLP-1 weight loss calculator to explore potential outcomes with either medication.
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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 — And Why It Matters
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways. Wegovy (semaglutide) activates only the GLP-1 pathway. This difference affects how they work and how your body responds.
- Mounjaro: dual mechanism may mean faster appetite suppression but also potentially higher nausea rates initially; maximum dose 15 mg once weekly; requires dose titration over 20 weeks
- Wegovy: single mechanism; maximum dose 2.4 mg once weekly; dose escalation over 16 weeks; potentially fewer GI side effects at lower doses but may require longer to reach therapeutic effect
- Clinical trial data: SURMOUNT-1 (Mounjaro) showed average clinically studied weight loss at maximum dose; STEP-1 (Wegovy) showed average clinically studied weight loss — but individual results vary significantly
- Prescriber choice: Your UK prescriber will recommend based on your health profile, not on average trial results
Clinically BackedWeight Loss
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Potential Drawbacks and Practical Considerations
Both medications carry similar side effects — nausea, diarrhoea, constipation, and stomach pain are very common, especially during dose escalation. Mounjaro cons include a longer titration schedule (20 weeks to maximum dose) and higher early nausea rates reported by some users. Wegovy cons include a lower maximum dose and potentially slower onset of appetite suppression. Cost varies significantly between private providers (typically £129–£320 monthly depending on dose). Neither medication is available on routine NHS prescription — access is through specialist tier 3/4 weight management services only, with significant waiting times in most areas. Both require ongoing clinical monitoring. Your GP or prescriber can assess which medication aligns best with your health needs, lifestyle, and treatment goals.
- 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 more effective than Wegovy?
Clinical trials show Mounjaro produced slightly higher average weight loss (20.9% vs 14.9%), but individual results vary considerably. Effectiveness depends on your metabolism, adherence, diet, and exercise — not just the medication. Your prescriber will recommend based on your personal health profile, not average trial data.
Which has fewer side effects, Mounjaro or Wegovy?
Both have similar side effect profiles — nausea, diarrhoea, constipation, and stomach pain are common with both. Mounjaro users report higher initial nausea during dose titration. Wegovy may cause fewer GI issues at lower doses. Individual tolerance varies widely. Discuss your specific concerns with your prescriber.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion formula — your prescriber will advise on timing and dosing if a switch is appropriate. Never stop one medication and start another without guidance.
How long does dose titration take with each medication?
Mounjaro requires approximately 20 weeks to reach maximum 15 mg dose (minimum 4 weeks at each dose level). Wegovy requires approximately 16 weeks to reach maximum 2.4 mg dose. Your prescriber may adjust timing based on side effects and individual response.
Are Mounjaro and Wegovy available on the NHS in the UK?
Both are NHS-approved for specialist tier 3/4 weight management services, but availability is very limited. Most people access these medications privately through GPhC-registered online pharmacies following a clinical assessment. NHS waiting times can be several months to years depending on your region.
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.