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 to Spot Fake Mounjaro in the UK
Counterfeit Mounjaro pens are a growing concern in the UK as demand for weight loss injections increases. Fake tirzepatide products pose serious health and safety risks. This guide explains how to identify genuine Mounjaro KwikPens, understand legitimate UK prescription routes (both NHS and private), and protect yourself when accessing this prescription-only weight management medication.
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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.
Signs of Genuine vs Counterfeit Mounjaro
Genuine Mounjaro KwikPens have specific security features you should always check:
- Authentic packaging: Genuine pens come in branded Eli Lilly boxes with clear UK labelling and batch numbers that are legible and match pharmacy records
- KwikPen appearance: The pre-filled pen should feel solid, have a sealed cap, and display "Mounjaro" clearly on the barrel with the dose (2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, or 15mg)
- Colour coding: Each dose has a specific colour-coded band — 2.5mg (grey), 5mg (purple), 7.5mg (light blue), 10mg (light green), 12.5mg (light pink), 15mg (orange)
- Temperature monitoring: Genuine pens have a temperature indicator card in the box that changes colour if exposed to heat — counterfeits often lack this
- Hologram and safety seals: Check for Eli Lilly security holograms on the box and intact safety seals on the pen itself
- QR code verification: Scan the QR code on the packaging — this should link to Eli Lilly's genuine product information
- Pharmacy documentation: You should receive a prescription receipt and full pharmacy documentation with every legitimate supply
Red flags include misspellings on packaging, blurry or missing logos, incorrect colour banding, missing temperature cards, and pens supplied without proper pharmacy documentation.
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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.
Safe UK Routes to Access Mounjaro
NHS route: Mounjaro prescribed through NHS specialist weight management services (tier 3). Your GP can refer you, though waiting times vary by region. Prescriptions are dispensed by NHS pharmacy — no cost to patients.
Private route: Through registered GPhC pharmacies following an online clinical assessment with a UK-licensed prescriber. Legitimate private providers ask detailed health questions, request medical records where necessary, and issue prescriptions that you can verify. Costs range from approximately £129–£320 per month depending on dose and provider. Always check the pharmacy is registered with the General Pharmaceutical Council (GPhC) — search the GPhC register online to verify legitimacy before purchasing.
What to expect: Any legitimate prescriber will ask about your BMI, medical history, current medications, contraindications, and weight loss goals. They will not assures specific weight loss results. Use our free GLP-1 weight loss calculator to understand potential outcomes based on clinical trial data before starting treatment.
- 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.
Where can I safely buy Mounjaro in the UK?
Through NHS specialist weight management services (after GP referral) or from GPhC-registered private pharmacies following an online clinical assessment with a UK-licensed prescriber. Always verify pharmacy registration via the GPhC register before purchasing. Never buy from unverified online sellers or social media sources.
What should I check on a genuine Mounjaro KwikPen?
Check for authentic Eli Lilly packaging with clear labelling, correct colour-coded bands matching the dose, intact safety seals, a temperature monitoring card, and a hologram. The pen barrel should clearly display "Mounjaro" and the dose. Scan the QR code to verify it links to genuine product information.
How much does Mounjaro cost privately in the UK?
Private Mounjaro typically costs between £129 and £320 per month, depending on dose and pharmacy. Costs vary because different providers source from different suppliers. Always ask for a total cost breakdown before starting treatment, including any consultation fees.
Why is counterfeit Mounjaro dangerous?
Counterfeit pens may contain no active ingredient, incorrect doses, contaminated solutions, or harmful substances. This can cause serious health complications, no weight loss benefit, wasted money, and potential infection or allergic reactions. Only purchase from verified, legitimate sources.
How do I verify a private pharmacy is legitimate?
Search the GPhC (General Pharmaceutical Council) register at www.pharmacyregulation.org using the pharmacy name. A legitimate GPhC-registered pharmacy will be listed with a registration number. Check they are licensed to supply prescription-only medicines and offer online consultations with UK-licensed prescribers.
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.