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 — What Do Clinical Reviews Show?
Mounjaro and Wegovy are both prescription-only weight loss injections licensed in the UK, but they work differently and deliver different results in clinical trials. This guide compares the two based on real evidence from clinical reviews, not marketing claims. Both are GLP-1 receptor agonists or related medications—Mounjaro (tirzepatide) is actually a dual GIP receptor and GLP-1 receptor agonist, making it mechanically unique. Understanding the differences helps you and your GP decide which might be more suitable for your individual situation.
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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 Differ — Clinical Trial Evidence
The key difference between Mounjaro and Wegovy lies in their mechanism. Wegovy (semaglutide) is a GLP-1 receptor agonist only—it signals one hormone pathway in your gut to reduce appetite and slow gastric emptying. Mounjaro (tirzepatide) activates two pathways: GIP receptor and GLP-1 receptor—this dual action may be why some people experience stronger appetite suppression in clinical trials.
Clinical trial comparisons show: SURMOUNT-1 (Mounjaro) reported approximately 15–21% average body weight loss at 72 weeks depending on dose. STEP-1 (Wegovy) reported approximately 14.9% average body weight loss at 68 weeks. Individual results vary significantly. Both doses escalate gradually over weeks—Mounjaro starts at 2.5 mg and reaches 15 mg maximum; Wegovy starts at 0.25 mg and reaches 2.4 mg maximum. Both are once-weekly injections delivered via pre-filled pens.
- Mounjaro: dual GIP+GLP-1 mechanism, potentially stronger appetite suppression
- Wegovy: single GLP-1 mechanism, longer track record in the market
- Both require a reduced-calorie diet and increased physical activity to work effectively
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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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Who Should Choose Which? Your GP's Role
Neither medication is universally "better"—suitability is personal. Your GP or prescriber will assess your medical history, current medications, and individual response to either drug. Some people tolerate one better than the other. Some prefer weekly dosing (both offer this). Cost and availability on the NHS or privately may also factor in. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses, but remember: these are estimates based on clinical averages, not assures.
Both medications carry similar common side effects: nausea, diarrhoea, constipation, and stomach pain—typically most severe in the first few weeks as your body adjusts. Serious side effects are rare but include pancreatitis symptoms and gallbladder problems. Neither is suitable for pregnant women, those under 18, or people with a history of severe gastroparesis. Your prescriber will discuss contraindications with you during your clinical assessment.
- 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 based on reviews?
Clinical trials show Mounjaro achieved slightly higher average weight loss (15–21% vs 14.9%), but differences are modest and individual results vary widely. Some people lose more on Wegovy, others on Mounjaro. Effectiveness depends on your metabolism, adherence, diet, and lifestyle—not just the drug itself.
Why does Mounjaro have a dual mechanism (GIP+GLP-1)?
Tirzepatide activates both GIP and GLP-1 receptors, which semaglutide (Wegovy) does not. The dual pathway may enhance appetite suppression and improve fat utilisation. Research suggests this may explain why some patients report stronger satiety with Mounjaro, though not everyone experiences this difference.
Which injection is available on the NHS in the UK?
Both Mounjaro and Wegovy can be prescribed through NHS specialist tier 3/4 weight management services following specialist assessment. Availability and waiting times vary by region and ICB. Private online prescribing is also available for both medications through GPhC-registered pharmacies.
Do Mounjaro and Wegovy have the same side effects?
Both have very similar common side effects: nausea, diarrhoea, vomiting, and constipation. Severity and duration vary between individuals. Mounjaro users report slightly more injection-site reactions in trials. Serious side effects (pancreatitis, gallbladder problems) are rare with both but require immediate GP attention if they occur.
Can I switch from Wegovy to Mounjaro or vice versa?
Yes, but only under prescriber guidance. There is no official established conversion dose between the two—approximate equivalences exist (e.g., 2.4 mg Wegovy ≈ 10–15 mg Mounjaro), but any switch must be managed individually by your prescriber based on your response and health status.
Ready to take control of your weight loss journey?
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