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 Is Mounjaro as a Diet Injection?
Mounjaro is a prescription-only weekly weight management injection licensed in the UK for adults with obesity or overweight conditions. It contains tirzepatide, a dual GLP-1 and GIP receptor agonist that works differently from other weight loss injections. Rather than being a "diet injection" in the traditional sense, Mounjaro is a medical treatment that, alongside a reduced-calorie diet and increased physical activity, may help reduce appetite and support weight loss. Individual results vary, and it requires a clinical assessment before prescription. This guide explains how it works, eligibility criteria, and what to expect in the UK.
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 as a Weight Management Treatment
Mounjaro is not a diet pill or appetite suppressant in the traditional sense. It's a prescription injection that activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). These hormones regulate appetite, hunger signals, and how quickly food leaves the stomach. When you use Mounjaro, these effects may help you feel fuller after smaller meals, reduce food cravings, and eat less overall — but only as part of a reduced-calorie diet and active lifestyle.
- GLP-1 activation: Signals to the brain that you're full, reducing appetite
- GIP activation: Supports fat utilisation and metabolic regulation
- Gastric slowdown: Food moves through the stomach more slowly, increasing satiety
Clinical trials showed that, on average, adults using Mounjaro alongside diet and exercise lost approximately 15–21% of their body weight. However, these results varied between individuals, and weight loss is not assured. Your GP or a licensed prescriber can assess whether this weekly weight loss injection is suitable for your personal situation.
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 Eligibility and How to Access It in the UK
You may be eligible for Mounjaro in the UK if you have:
- A BMI of 30 kg/m² or above (obesity), OR
- A BMI of 27–29.9 kg/m² (overweight) with at least one weight-related health condition — such as type 2 diabetes, prediabetes, high blood pressure, or sleep apnoea
- If you're of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds (from 27.5 kg/m²) may apply
Access in the UK is through NHS specialist weight management services (tier 3) or private online prescribing following a clinical assessment. NHS referral paths vary by region and often have waiting lists. Private access is available through GPhC-registered pharmacies. Use our free BMI calculator to check your personal BMI, and our GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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 a diet injection?
Mounjaro is a prescription weight management injection, not a diet pill. It's a GLP-1 and GIP receptor agonist that works alongside diet and exercise. It is not a traditional appetite suppressant or diet drug — it's a medical treatment that requires prescription and clinical assessment by a UK healthcare professional.
How often do you inject Mounjaro for weight loss?
Mounjaro is a once-weekly injection. You inject yourself (or someone can help) at the same time each week. Each pre-filled KwikPen contains four weekly doses. Doses range from 2.5 mg to 15 mg, with gradual increases every four weeks to find the right level for you.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) activates only the GLP-1 pathway. Clinical trials showed Mounjaro averaged slightly higher weight loss (up to 20.9% vs 14.9%), but individual results vary. Both are prescription-only and require clinical assessment. Your prescriber will recommend whichever is most appropriate for you.
Can I get Mounjaro on the NHS in the UK?
Mounjaro is approved by NICE for NHS use through specialist tier 3 weight management services. However, NHS access varies significantly by region and availability. Many areas have long waiting lists. Private access is available through online prescribing services following a clinical assessment. Speak to your GP about referral options in your area.
What are the main side effects of Mounjaro as a weekly injection?
The most common side effects include nausea, diarrhoea, vomiting, constipation, and stomach pain — especially when starting or increasing doses. These often improve over time. Serious side effects are rare but may include severe stomach pain (possible pancreatitis) or allergic reactions. Always report unexpected symptoms to your prescriber immediately.
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.