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 Purchase Mounjaro Online — Comparing Mounjaro and Wegovy
If you're researching how to purchase Mounjaro online in the UK, you may also want to understand how it compares to Wegovy, the other main GLP-1 weight management injection available. Both are prescription-only medications that require a clinical assessment from a UK-licensed prescriber before purchase. This guide explains the key differences between Mounjaro (tirzepatide) and Wegovy (semaglutide), their mechanisms, clinical trial results, and how eligibility and access work for both medications in the UK.
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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.
Mounjaro vs Wegovy: Mechanism and Clinical Trial Data
Mounjaro (tirzepatide) and Wegovy (semaglutide) work through different biological mechanisms. Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two separate hormone pathways in the body — this dual action may contribute to stronger appetite suppression and metabolic effects. Wegovy is a GLP-1 receptor agonist only, activating a single pathway. In clinical trials, Mounjaro showed average weight loss of approximately 15–21% of body weight across doses (SURMOUNT-1 trial), while Wegovy showed average weight loss of approximately 14.9% at its maximum dose (STEP-1 trial). However, these are clinical trial averages alongside reduced-calorie diet and increased physical activity — individual results vary significantly. Neither medication assures weight loss, and prescriber choice depends on individual health factors, not trial percentages alone.
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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.
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Doses, Side Effects, and Eligibility Differences
Doses: Mounjaro starts at 2.5 mg weekly and escalates to a maximum of 15 mg weekly. Wegovy starts at 0.25 mg weekly and escalates to a maximum of 2.4 mg weekly — much lower absolute doses because of their different potencies. Side effects are similar between both: nausea, diarrhoea, constipation, vomiting, and stomach pain are common. Eligibility is identical for both: adults with a BMI of 30 or above, or 27 or above with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea. Lower BMI thresholds apply for South Asian, Chinese, Black African, and Black Caribbean adults. Both require a prescription from a UK-licensed prescriber and both can be purchased online through GPhC-registered pharmacies following an online clinical assessment.
- 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.
Can I buy Mounjaro online without a prescription in the UK?
No. Mounjaro is prescription-only in the UK. You cannot legally purchase it without a valid prescription from a UK-licensed prescriber. Online prescribing services conduct a clinical assessment and issue a prescription if appropriate, but a prescription is always required. Never purchase from unlicensed sellers.
Which is more effective, Mounjaro or Wegovy?
Clinical trials showed slightly higher average weight loss with Mounjaro (15–21%) than Wegovy (14.9%), but these are averages only. Individual results vary significantly based on genetics, lifestyle, and how your body responds. Your prescriber will recommend the most suitable option for your personal health profile, not based on trial percentages alone.
How much does Mounjaro cost to purchase online in the UK?
Private costs vary by dose and pharmacy, typically ranging from £129 to £320 per month. NHS access is limited to specialist tier 3/4 weight management services and availability varies by region. Check with multiple GPhC-registered providers for current pricing and always confirm the cost includes the prescription fee and medication.
Is Mounjaro available on the NHS in the UK?
NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. However, availability is limited and varies significantly by region. NHS access requires referral to a specialist tier 3/4 service from your GP, and waiting lists can be very long. Many people access Mounjaro privately through online prescribing instead.
Can I switch between Mounjaro and Wegovy?
Yes, but any switch must be managed by your prescriber. Approximate dose equivalences exist (5 mg Mounjaro ≈ 0.5 mg Wegovy; 10 mg ≈ 1.7 mg; 15 mg ≈ 2.4 mg), but these are not official conversions. Never self-switch medications. Contact your prescriber if you want to discuss changing to the alternative medication.
Ready to take control of your weight loss journey?
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