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 Mounjaro Do To Your Body?
Mounjaro is a prescription-only weight management injection that works differently in your body compared to other weight loss treatments. Understanding how tirzepatide (the active ingredient in Mounjaro) affects your system — and how to access it in the UK — can help you decide if this treatment is right for you. This guide explains the mechanisms, effects, costs, and routes to getting Mounjaro in the UK, whether through the NHS or private prescription.
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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.
How Mounjaro Works: The Dual Mechanism
Mounjaro is a dual GIP and GLP-1 receptor agonist — this dual mechanism is what sets it apart from other weight loss injections like Wegovy. It activates two natural hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). When you inject your weekly dose from the Mounjaro KwikPen, tirzepatide mimics these hormones to send signals to your brain that reduce hunger and increase feelings of fullness. This means you eat less and feel satisfied sooner.
The medication also slows gastric emptying — how quickly food leaves your stomach — allowing you to feel fuller for longer after meals. Additionally, Mounjaro affects how your body uses fat stores and helps regulate blood sugar levels. These combined effects support weight loss when combined with a reduced-calorie diet and increased physical activity. Clinical trials showed that people taking Mounjaro lost an average of 15–21% of their body weight, though individual results vary significantly.
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.
Cost, Access & How to Get Mounjaro in the UK
In the UK, Mounjaro is available through two routes: NHS specialist services and private prescription. NHS access is through tier 3 or tier 4 weight management services following a referral from your GP — however, availability varies dramatically by region, and waiting lists can be very long (often months to years). Private prescription is available without NHS referral through online consultations with UK-licensed prescribers, with costs ranging from approximately £130–£320 per month depending on your dose.
To access Mounjaro privately, you complete an online health assessment, and if approved by the prescriber, your prescription is dispensed by a GPhC-registered pharmacy. You'll then self-inject once weekly. Use our GLP-1 weight loss calculator to estimate potential results at different doses, and our BMI calculator to check whether you might be eligible (typically BMI 30+ or 27+ with health conditions).
- 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.
How long does it take for Mounjaro to work?
Most people notice appetite reduction within the first 1–2 weeks of starting Mounjaro. Measurable weight loss typically becomes evident after 4–8 weeks. Your dose is increased every 4 weeks, and maximum effect is usually seen after reaching your target maintenance dose (often 10–15 mg weekly). Results vary individually.
Will I lose weight immediately on Mounjaro?
Not immediately. The first dose (2.5 mg) is low and designed for adjustment. Meaningful weight loss usually appears after 4+ weeks as your dose builds and your body adjusts. The medication works best alongside a reduced-calorie diet and physical activity — it's not a standalone solution.
What is the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) has a dual GIP+GLP-1 mechanism, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, but results vary. Both are once-weekly injections; Mounjaro has a higher maximum dose (15 mg vs 2.4 mg). Your prescriber will advise which is appropriate for you.
Can I get Mounjaro on the NHS in the UK?
Yes, but access is limited. NICE has approved tirzepatide for NHS specialist weight management services. Availability depends on your local integrated care board (ICB). You'll need a GP referral to tier 3 services. Many areas have long waiting lists. Private prescription is an alternative without NHS waiting times.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £130–£320 per month depending on your dose and the provider. Starting doses (2.5–5 mg) are less expensive; higher maintenance doses (10–15 mg) cost more. Prices vary between providers, so comparing options is worthwhile. Always ensure you're using a GPhC-registered pharmacy.
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.