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
What Does The Mounjaro Injection Do?
Mounjaro (tirzepatide) is a prescription-only weekly injection that works by activating two natural hormone pathways in your body to help support weight management. Unlike other weight loss injections that work through a single mechanism, Mounjaro uses a dual GIP and GLP-1 receptor agonist approach—meaning it works in two complementary ways to help reduce appetite, support feeling fuller after meals, and assist with weight loss alongside a reduced-calorie diet and increased physical activity. It's approved by the MHRA in the UK and available through both NHS specialist weight management services and private prescription routes. Use our free GLP-1 weight loss calculator to explore how Mounjaro may support your individual weight management goals.
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: The Dual Hormone Mechanism
Mounjaro's unique strength lies in its dual action on two natural hormone systems. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) are hormones your body naturally produces after eating. Mounjaro mimics and amplifies these signals, creating a combined effect that:
- Reduces appetite and food cravings by signalling fullness to your brain
- Helps you feel satisfied after smaller portions
- Slows gastric emptying—how quickly food moves through your stomach
- Supports improved appetite control throughout the day
This dual mechanism may explain why clinical trial data showed Mounjaro helped participants achieve an average of 15–clinically studied weight loss at various doses, though individual results vary significantly. Each person responds differently depending on their starting weight, lifestyle changes, and adherence to the injection schedule.
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.
Mounjaro in NHS Weight Management Services
NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services, marking it as an option for eligible adults. Access is through tier 3 specialist services following referral from your GP—not as a standard prescription from primary care. Eligibility criteria include:
- BMI of 30 kg/m² or above, OR BMI of 27–29.9 with a weight-related health condition
- Lower thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults (BMI 27.5+)
- Adults aged 18 and over
NHS availability varies significantly by region and integrated care board. Many areas have substantial waiting lists. Your GP can discuss whether specialist weight management services are appropriate for you and help with referral where available.
- 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 insulin?
No. Mounjaro is not insulin and does not work like insulin. It's a GIP and GLP-1 receptor agonist that mimics natural hormones produced after eating. It helps regulate appetite and blood sugar control differently from insulin therapy.
How often do you inject Mounjaro?
Mounjaro is a once-weekly injection. You use a pre-filled KwikPen device and inject the same day each week. Each pen contains four weeks' worth of doses. Doses range from 2.5 mg to 15 mg depending on your personalised titration schedule.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist, while Wegovy (semaglutide) is a GLP-1-only agonist. Mounjaro's dual mechanism may offer different weight loss results. Both are weekly injections, prescription-only, and require clinical assessment before prescribing.
Can I get Mounjaro on the NHS?
Yes, Mounjaro is approved by NICE for NHS specialist weight management services. Access requires referral to tier 3 services from your GP. Availability and waiting times vary significantly by region. Private prescription routes are also available through GPhC-registered online providers.
What happens if I stop taking Mounjaro?
If you stop Mounjaro, its effects gradually wear off over several weeks. Weight regain is common if lifestyle changes (diet and physical activity) are not maintained. Always discuss stopping Mounjaro with your prescriber rather than stopping abruptly.
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.