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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How Mounjaro Works as a GLP-1 Receptor Agonist
Mounjaro (tirzepatide) is a prescription-only weight management injection that works differently from other GLP-1 medications available in the UK. While most GLP-1 drugs activate a single hormone pathway, Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it targets two natural signalling pathways in your body to help regulate appetite and support weight management. This dual mechanism is what makes Mounjaro distinct from other weight loss injections like Wegovy, which contains semaglutide, a GLP-1 agonist only.
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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.
The Dual GLP-1 and GIP Mechanism Behind Mounjaro
Mounjaro activates two hormone pathways:
- GLP-1 (glucagon-like peptide-1): A natural hormone that signals to your brain that you are full, reduces appetite, and slows how quickly food leaves your stomach. This helps you feel satisfied after smaller meals.
- GIP (glucose-dependent insulinotropic polypeptide): A second hormone pathway that supports blood sugar regulation and may enhance the weight management effect beyond GLP-1 alone.
By activating both pathways, Mounjaro may provide a stronger appetite-suppressing effect than single-pathway GLP-1 agonists. Clinical trials using Mounjaro showed average weight loss of approximately 15–21% of body weight over 72 weeks, alongside a reduced-calorie diet and increased physical activity. However, individual results vary significantly, and weight loss is not assured. Mounjaro is injected once weekly using a pre-filled KwikPen device, with doses ranging from 2.5 mg to 15 mg.
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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 GLP-1 Weight Loss Medications
In the UK, three prescription-only medications are licensed for weight management: Mounjaro (tirzepatide), Wegovy (semaglutide), and Saxenda (liraglutide). Mounjaro and Wegovy are both once-weekly injections, whereas Saxenda is a daily injection. The key difference is mechanism: Wegovy is a GLP-1 agonist only, while Mounjaro is a dual GIP and GLP-1 agonist. Some clinical evidence suggests the dual action of Mounjaro may lead to slightly greater weight loss than single-pathway GLP-1 drugs, but results depend on individual factors including adherence, diet, exercise, and metabolism. Your GP or a licensed prescriber will assess which medication is most appropriate for your individual health needs following a 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 the same as Wegovy?
No. Both are prescription-only weight loss injections available in the UK, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro is given once weekly at doses up to 15 mg, while Wegovy's maximum dose is 2.4 mg. Clinical trial data suggests different weight loss profiles, but individual results vary.
What is a GLP-1 receptor agonist?
A GLP-1 receptor agonist is a medication that mimics GLP-1, a natural hormone your gut produces after eating. GLP-1 signals your brain that you are full, reduces hunger, and slows stomach emptying. Mounjaro goes further by also activating GIP, a second hormone pathway. This dual action may help you feel fuller on smaller portions and manage appetite more effectively.
How much weight can I expect to lose with Mounjaro?
Clinical trials showed an average weight loss of 15–21% of body weight over 72 weeks, depending on dose and adherence. However, this is an average — individual results vary significantly based on genetics, diet, exercise, metabolism, and other factors. Weight loss is not assured. Use our free GLP-1 weight loss calculator to see potential outcomes at different doses.
Is Mounjaro available on the NHS in the UK?
Yes, tirzepatide (Mounjaro) has been approved by NICE for NHS use within specialist tier 3 weight management services. However, availability varies significantly by region and ICB. Many areas have waiting lists of several months to over a year. Private access through online prescribing is available without NHS referral.
What makes Mounjaro different from other GLP-1 drugs?
Mounjaro's dual GIP and GLP-1 mechanism sets it apart. While Wegovy and Saxenda activate the GLP-1 pathway alone, Mounjaro activates both GIP and GLP-1, potentially amplifying appetite suppression and metabolic effects. This dual action is why some people may experience different results with Mounjaro compared to single-pathway GLP-1 medications. ```
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