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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Is GLP-1 The Same As Mounjaro?
No, GLP-1 and Mounjaro are not the same thing. GLP-1 is a natural hormone pathway that regulates appetite and blood sugar. Mounjaro (tirzepatide) is a prescription-only injection that activates two hormone pathways: GLP-1 and GIP. Understanding the difference is important if you're exploring weight management options in the UK. This guide explains what each is, how they differ, and what that means for you.
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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.
What Is GLP-1 And How Does It Work?
GLP-1 (glucagon-like peptide-1) is a natural hormone produced in your gut after eating. It sends signals to your brain that you're full, which helps regulate appetite and food intake. GLP-1 also stimulates insulin release in response to food and slows how quickly food leaves your stomach.
GLP-1 receptor agonist medications work by mimicking and amplifying these natural effects. This hormone pathway is the foundation of several weight management medications licensed in the UK, including Wegovy (semaglutide) and Saxenda (liraglutide). Both are GLP-1-only medications. They activate the GLP-1 pathway to reduce appetite and support weight loss alongside a reduced-calorie diet and increased physical activity. Clinical trials showed that GLP-1 medications can help people lose an average of 15% of their body weight, though individual results vary significantly.
You can estimate potential weight loss outcomes using our GLP-1 weight loss calculator, which projects results at different doses based on clinical trial data.
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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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How Is Mounjaro Different From GLP-1 Medications?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two hormone pathways, not just one. GIP (glucose-dependent insulinotropic polypeptide) is a second natural hormone involved in appetite regulation and blood sugar control. By targeting both pathways simultaneously, Mounjaro may offer a different effect compared to GLP-1-only medications like Wegovy.
In the SURMOUNT clinical trials, Mounjaro showed an average weight loss of approximately 15–21% of body weight at the maximum dose (15 mg), compared to around 15% for GLP-1-only medications in their trials. However, individual responses vary. Both are prescription-only medicines requiring clinical assessment. Your GP or a licensed prescriber can discuss which approach might be suitable for your individual 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.
Is Mounjaro a GLP-1 medication?
Mounjaro is not a GLP-1-only medication. It's a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. This dual mechanism is the key difference between Mounjaro and medications like Wegovy, which target GLP-1 alone.
Can I switch from a GLP-1 medication to Mounjaro?
Switching between medications should only be done under medical supervision. There is no official established conversion chart between GLP-1 medications and Mounjaro. Approximate dose equivalences exist based on clinical practice, but any switch must be managed by your prescriber to ensure safety and effectiveness.
Why would someone choose Mounjaro over a GLP-1 medication?
The dual mechanism of Mounjaro may appeal to some people, and clinical trials suggested slightly higher average weight loss compared to some GLP-1-only medications. However, individual results vary significantly. Your prescriber will assess which medication is most appropriate based on your health profile and eligibility.
Are Mounjaro and Ozempic the same thing?
No. Ozempic contains semaglutide (the same active ingredient as Wegovy) but is approved for type 2 diabetes, not weight loss. Mounjaro contains tirzepatide and is approved specifically for weight management in the UK. They are different medications with different mechanisms and approvals.
Where can I get Mounjaro or GLP-1 medications in the UK?
Both are prescription-only medicines available through NHS specialist weight management services (tier 3) or private online prescribing via a UK-licensed prescriber. NHS access is through referral from your GP and availability varies by region. Private access is available without NHS referral following an online clinical assessment.
Ready to take control of your weight loss journey?
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