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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Compare Mounjaro: How Does It Stack Up?
If you're considering weight loss treatment in the UK, you may have heard about Mounjaro (tirzepatide) and want to understand how it compares to other options. Mounjaro is a prescription-only injection that works differently to some alternatives because it activates two hormone pathways rather than one. This guide explains how Mounjaro works, who can access it, what doses are available, and how it compares to other weight management treatments available in the UK. Always consult your GP or a licensed prescriber to find out which option is right for your individual circumstances.
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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 Works and What Makes It Different
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways in your body. This dual mechanism is what sets it apart from some other weight loss injections. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are hormones that help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. Mounjaro also slows how quickly food leaves your stomach, though this effect typically reduces over time. You inject Mounjaro once per week using a pre-filled KwikPen device.
Doses range from 2.5 mg to 15 mg, with titration (gradual increases) over several weeks. In clinical trials (SURMOUNT-1), participants on Mounjaro lost an average of 15–21% of their body weight over 72 weeks when combined with a reduced-calorie diet and increased physical activity—though individual results vary significantly. Your prescriber will assess whether Mounjaro is appropriate for you and determine the best starting dose.
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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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Mounjaro vs Other Weight Loss Options: Key Comparisons
Mounjaro vs Wegovy (semaglutide): Both are once-weekly injections and prescription-only. Wegovy is a GLP-1 agonist (single mechanism), while Mounjaro is a dual GIP/GLP-1 agonist. Clinical trial data shows Mounjaro users lost approximately 15–21% body weight, compared to around 15% with Wegovy at its maximum dose—though results vary between individuals and cannot be assured. Maximum doses differ: Mounjaro goes up to 15 mg, Wegovy to 2.4 mg.
Both require a clinical assessment before prescription. Access in the UK is either through NHS specialist weight management services (tier 3) or private online prescribing following a consultation. Use our free GLP-1 weight loss calculator above to explore potential weight loss estimates at different doses and understand what realistic expectations might be for your circumstances.
- 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.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is available through NHS specialist weight management services (tier 3). Access varies significantly by region and NHS Integrated Care Board (ICB). You'll need a GP referral to specialist services. Waiting lists can be very long in many areas. Private prescribing is also available through registered online services following a clinical assessment—this doesn't require an NHS referral.
What's the difference between Mounjaro and tirzepatide?
Mounjaro is the brand name for tirzepatide. "Tirzepatide" is the active ingredient—the medicine itself. Mounjaro is how it's marketed and sold in the UK. They're the same medication. When your GP or prescriber discusses your treatment, they may use either term interchangeably.
Is Mounjaro better than Wegovy?
Both are effective weight loss medications with different mechanisms. Clinical trials show Mounjaro users lost slightly more weight on average (15–21% vs ~15%), but individual results vary greatly and depend on many factors including adherence, lifestyle changes, and personal physiology. Your prescriber will advise which is more suitable for your health profile and circumstances.
How does the Mounjaro KwikPen work?
The Mounjaro KwikPen is a pre-filled auto-injection pen. You inject once weekly into your stomach, thigh, or upper arm (arm requires assistance). Each pen contains four weekly doses. Store unopened pens in the fridge at 2–8°C. After first use, you can store at room temperature below 30°C for up to 30 days. Always check your pen before injecting.
Who is eligible for Mounjaro in the UK?
You may be eligible if you have a BMI of 30 or above, or BMI 27–29.9 with at least one weight-related health condition (type 2 diabetes, prediabetes, high blood pressure, sleep apnoea, or cardiovascular disease). For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. A prescriber will assess your individual eligibility following a clinical consultation. ```
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