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
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How Does Mounjaro Work for Weight Loss in the UK?
Mounjaro (tirzepatide) is a prescription-only weekly weight loss injection that works as a dual GIP and GLP-1 receptor agonist—a mechanism that sets it apart from other weight loss medications. Understanding how it works, combined with what it actually costs and how to access it in the UK, helps you make informed decisions about whether this option might suit your health goals. This guide explains the science, the costs, and your realistic options for getting Mounjaro through both NHS and private routes.
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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 Explained
Mounjaro's effectiveness comes from its unique dual action. Unlike a single GLP-1 receptor agonist like semaglutide, tirzepatide activates both GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 receptor pathways. These are natural hormones your gut produces after eating.
GLP-1 signals fullness to your brain, reduces appetite, and slows how quickly food leaves your stomach. GIP helps regulate how your body uses fat. Together, they create a stronger appetite-suppressing effect than either pathway alone. Clinical trials show this dual mechanism may help users lose an average of 15–21% of their body weight over 72 weeks—though individual results vary significantly and depend on dose, diet, and activity level.
Mounjaro comes as a pre-filled KwikPen device injected once weekly under the skin. Doses start at 2.5 mg and escalate to a maximum of 15 mg weekly based on tolerance and response.
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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 Cost in the UK: NHS Access vs Private Route
NHS access: NICE has approved tirzepatide for NHS specialist weight management services, but access is highly limited and varies by region. You'll need a GP referral to a tier 3/4 specialist weight management service, and waiting lists can stretch many months or years depending on your area. If approved through the NHS, you pay only your standard prescription fee (currently £9.90 in England).
Private prescription route: Private prescribers offer faster access. Following an online consultation, if approved, private prescriptions typically cost £129–£320 per month depending on your dose and provider. This includes the clinical assessment and prescription. Private dispensing through GPhC-registered pharmacies means you access medication without NHS referral.
Try our free GLP-1 weight loss calculator to estimate potential results at different doses, which may help inform your decision.
- 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 does the GIP receptor do in Mounjaro?
GIP (glucose-dependent insulinotropic polypeptide) is a natural gut hormone that Mounjaro activates alongside GLP-1. It helps regulate fat utilisation and enhances the overall appetite-suppressing effect, which is why tirzepatide's dual mechanism may produce greater average weight loss than single GLP-1 medications like semaglutide.
How much does Mounjaro cost privately in the UK?
Private Mounjaro prescriptions typically range from £129–£320 per month depending on your dose (2.5 mg to 15 mg weekly). This covers the clinical consultation, prescription, and medication. Prices vary between providers, so it's worth comparing. Always ensure you're using a GPhC-registered pharmacy.
Can I get Mounjaro on the NHS in the UK?
NICE has approved tirzepatide for NHS specialist weight management services, but access is limited and varies by region. You need a GP referral to a tier 3/4 specialist service. Waiting lists are often very long. If approved, you pay only the standard prescription fee (£9.90 in England). Private routes offer faster access but at higher cost.
How is Mounjaro different from Wegovy for weight loss?
Both are weekly injections for weight loss, but they work differently. Mounjaro (tirzepatide) is a dual GIP + GLP-1 agonist; Wegovy (semaglutide) activates GLP-1 only. Clinical trials suggest Mounjaro may produce slightly higher average weight loss (15–21% vs ~15%), though individual results vary. Your prescriber can advise which might suit you.
What happens after I get a Mounjaro prescription online?
After your online consultation with a UK-licensed prescriber, if approved, your prescription goes to a GPhC-registered pharmacy. They dispense your KwikPens (usually a 4-week supply per order). You inject once weekly at home. You'll need follow-up consultations with your prescriber to monitor progress and discuss any side effects or dose adjustments.
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.