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
Free tracker included with every download this week
Understanding Mounjaro for Weight Management in the UK
Mounjaro (tirzepatide) is a prescription-only injection licensed for weight management in UK adults. It works differently from other weight loss medications because it activates two natural hormone pathways—GIP and GLP-1—rather than just one. If you've heard about "slimming injections" or weight loss jabs in the UK, Mounjaro is one of the newer options available. This guide explains how it works, who can access it, what to expect, and how it compares to alternatives like Wegovy. Our free BMI calculator and GLP-1 weight loss calculator can help you understand your current health status and estimate potential outcomes.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 Sets It Apart
Mounjaro is a dual GIP and GLP-1 receptor agonist — meaning it activates two separate hormone pathways in your body. GLP-1 (glucagon-like peptide-1) and GIP (glucose-dependent insulinotropic polypeptide) both signal to your brain that you're full, reduce food cravings, and slow how quickly food leaves your stomach. This dual mechanism may help you feel satisfied with smaller portions and eat less overall.
Unlike Wegovy (semaglutide), which targets only the GLP-1 pathway, Mounjaro's additional GIP activation may provide stronger appetite suppression for some people. Clinical trials showed that adults using Mounjaro lost an average of 15–21% of their body weight over 72 weeks, though individual results vary significantly. It's delivered as a once-weekly injection using a pre-filled pen.
- Dual hormone pathway activation (GIP + GLP-1)
- Once-weekly injection via KwikPen device
- Doses range from 2.5 mg to 15 mg
- Results achieved alongside reduced-calorie diet and exercise
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
UK Eligibility, Access, and What to Expect
In the UK, you may be eligible for Mounjaro if you have a BMI of 30 or above, or a BMI of 27–29.9 with weight-related health conditions like high blood pressure, type 2 diabetes, or sleep apnoea. Lower BMI thresholds (27.5+) apply to adults of South Asian, Chinese, Black African, or Black Caribbean heritage. You can access Mounjaro through NHS specialist weight management services (tier 3) or privately via a GPhC-registered online pharmacy following a clinical assessment.
Common side effects include nausea, diarrhoea, and reduced appetite—most ease over time. Weight loss is not assured, and you'll need to combine medication with a reduced-calorie diet and physical activity. Use our free weight loss calculator to estimate potential outcomes at different doses, and our progress tracker to monitor your journey over time.
- 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 Ozempic?
No. Both contain semaglutide, but Ozempic (up to 2 mg) is licensed for type 2 diabetes, while Mounjaro (up to 15 mg tirzepatide) is licensed specifically for weight management. Mounjaro uses tirzepatide (a different drug), not semaglutide. Never use Ozempic off-label for weight loss—always use the licensed weight management medication prescribed by your healthcare provider.
How much weight can I lose on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks at the highest dose (15 mg), alongside diet and exercise. However, individual results vary significantly—some people lose more, some less. Your GP or prescriber can discuss realistic expectations based on your personal health. Use our GLP-1 calculator for an estimate.
Can I get Mounjaro on the NHS in the UK?
Possibly. NICE has approved tirzepatide for NHS specialist weight management services (tier 3), but availability varies significantly by region and NHS trust. Waiting lists can be very long. Many people access Mounjaro privately through online prescribing services, which offer faster access but require payment (typically £129–£320 per month).
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) uses a dual GIP + GLP-1 mechanism and may provide slightly stronger appetite suppression. Wegovy (semaglutide) uses GLP-1 alone. Both are once-weekly injections. Average weight loss is similar (14–21%), but results vary individually. Your prescriber can advise which is more suitable for you based on your health profile.
Will I regain weight if I stop Mounjaro?
Weight regain is common after stopping any weight loss medication if diet and exercise habits don't remain in place. Mounjaro works best as part of a long-term approach including sustainable dietary changes and physical activity. Your prescriber can discuss the best plan for your individual situation and whether ongoing treatment is appropriate.
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.