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 Online vs Wegovy — What's the Difference?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available online in the UK through licensed prescribers. While both are once-weekly GLP-1-based medications, they work differently and produce different average weight loss results. This guide compares the two side-by-side so you understand the key differences before seeking a clinical assessment. Individual results vary significantly, and the right choice depends on your personal health profile and prescriber recommendation.
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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
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. This means it activates two hormone pathways in your body simultaneously — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual action may enhance appetite suppression and help regulate fat utilisation more effectively than single-pathway medications.
Wegovy (semaglutide) is a GLP-1-only receptor agonist. It activates just the GLP-1 pathway, which reduces appetite and helps you feel fuller after smaller meals. Both medications slow gastric emptying (how quickly food leaves your stomach), though this effect often diminishes over time.
Clinical trial results from SURMOUNT-1 (Mounjaro) and STEP-1 (Wegovy) show Mounjaro achieved average weight loss of approximately 20.9% at the maximum 15 mg dose, while Wegovy achieved approximately 14.9% at its maximum 2.4 mg dose — though these are averages and individual outcomes vary considerably.
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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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Eligibility, Access, and Which Might Suit You
Both medications require the same UK eligibility criteria: a BMI of 30 or above, or BMI of 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or sleep apnoea. Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. Both are prescription-only and require a clinical assessment before being prescribed.
The choice between them is not yours alone — it's determined by your prescriber based on your medical history, other medications you take, and individual suitability. Some people respond better to one than the other. Your GP or a licensed online prescriber will assess which is appropriate for you. Use our GLP-1 weight loss calculator to understand potential outcomes at different doses for either medication, and our BMI calculator to check your current category.
- 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 stronger than Wegovy?
Mounjaro's dual mechanism (GIP+GLP-1) and higher maximum dose (15 mg vs 2.4 mg) produced greater average weight loss in clinical trials. However, "stronger" isn't accurate — they work differently, and individual response varies. Some people respond better to Wegovy. Your prescriber will choose based on your health profile, not on perceived strength.
Which is easier to inject — Mounjaro or Wegovy?
Both are once-weekly pre-filled pen injections equally easy to use. Mounjaro comes as a KwikPen, Wegovy as an auto-injection pen. Both are stored in the fridge when unopened. The injection technique is similar. Either is straightforward for self-administration after training.
What if Mounjaro or Wegovy doesn't work for me?
If one medication isn't producing results after sufficient time on the maximum dose, your prescriber may switch you to the alternative or explore other options. Switching between GLP-1 medications does happen in clinical practice, though any change must be managed by your prescriber.
Can I get Mounjaro or Wegovy through the NHS?
Both are available through NHS specialist weight management (tier 3) services, but access is limited and varies by region. Waiting lists can be very long. Private online prescription is more accessible — both are available through GPhC-registered online pharmacies following a clinical assessment.
Which has fewer side effects — Mounjaro or Wegovy?
Side effects are similar between both (nausea, diarrhoea, constipation, stomach pain). Individual tolerance varies. Starting at a low dose and increasing gradually helps most people adjust. Your prescriber will discuss side effect management with you regardless of which medication you're prescribed.
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.