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
Best Place for Mounjaro Injections vs Wegovy
If you're considering weight loss injections in the UK, you may be comparing Mounjaro and Wegovy — two prescription-only medications with different mechanisms and clinical profiles. Both are licensed for weight management in UK adults, but they're not identical. This guide explains where to inject each medication, how they differ, and what the clinical trial evidence shows so you can understand the differences clearly. Your prescriber will help you decide which is right for your individual situation.
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 and Wegovy Differ — Mechanism and Trial Results
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — meaning it activates two separate hormone pathways in the body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This difference affects how they work and clinical outcomes.
In the SURMOUNT-1 clinical trial, Mounjaro at maximum dose (15 mg once weekly) achieved average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at maximum dose (2.4 mg once weekly) achieved average weight loss of approximately 14.9% over 68 weeks. Both results were achieved alongside reduced-calorie diet and increased physical activity. Individual results vary significantly — these are trial averages, not assured outcomes for any person. Both medications are injected once weekly, though Mounjaro uses a KwikPen and Wegovy uses an auto-injection pen.
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.
Injection Sites and Suitability — What Your Prescriber Considers
Both Mounjaro and Wegovy are injected into the same three body sites: the stomach (abdomen), upper thigh, or upper arm. You rotate the injection site each week to avoid tissue damage. The best choice between these two medications depends on your individual health profile, not the injection location.
Your prescriber will assess your eligibility based on BMI, weight-related health conditions, and current medications. Both require a clinical assessment before prescription. Use our free GLP-1 weight loss calculator to see projected weight loss outcomes at different doses for each medication, and check your BMI using our BMI calculator to understand your starting point. Individual suitability is a clinical decision — discuss your options with your GP or a licensed prescriber.
- 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.
What's the main difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist activating two hormone pathways. Wegovy (semaglutide) is a GLP-1 agonist activating one pathway. This mechanism difference contributes to different clinical trial outcomes and individual responses. Both are prescription-only once-weekly injections licensed for UK weight management.
Which one causes more weight loss — Mounjaro or Wegovy?
In clinical trials, Mounjaro at maximum dose showed higher average weight loss (20.9%) than Wegovy (14.9%). However, individual results vary significantly based on genetics, lifestyle, and personal response. Neither result is assured for any individual. Your prescriber will help determine which is more suitable for you.
Are injection sites the same for both medications?
Yes — both Mounjaro and Wegovy are injected into the stomach, upper thigh, or upper arm. You rotate sites weekly. Injection location is not the deciding factor between the two; clinical assessment and individual suitability determine which medication is prescribed.
Do both require a prescription and clinical assessment in the UK?
Yes, both Mounjaro and Wegovy are prescription-only medications in the UK. Both require a clinical assessment by a UK-licensed prescriber before prescription. You can access them through NHS specialist weight management services or private online prescribing, depending on your circumstances and local availability.
Which medication is available on the NHS in the UK?
NICE has approved both tirzepatide (Mounjaro) and semaglutide (Wegovy) for NHS use within specialist tier 3 weight management services. Availability and waiting times vary significantly by region. Private access is available through GPhC-registered online pharmacies following a clinical assessment without NHS referral.
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.