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
Is Mounjaro Prescription Only?
Yes, Mounjaro (tirzepatide) is prescription-only in the UK — you cannot buy it over the counter. Like Wegovy, it requires a clinical assessment from a GP or licensed prescriber before being dispensed. Both are once-weekly injectable weight loss medications, but they work slightly differently. Understanding the prescription requirements and how they compare can help you decide which option might suit your situation. Use our free BMI calculator to check your starting point, and our GLP-1 weight loss calculator to see potential outcomes with either 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.
Mounjaro vs Wegovy: Prescription Status and Trial Data
Both Mounjaro and Wegovy are prescription-only medicines in the UK — neither is available without a clinical assessment. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways. Wegovy (semaglutide) is a GLP-1-only agonist. In clinical trials, Mounjaro users lost an average of 20.9% of their body weight at the maximum 15 mg dose (SURMOUNT-1 trial), whilst Wegovy users lost approximately 14.9% at 2.4 mg (STEP-1 trial). However, individual results vary significantly, and both require a reduced-calorie diet and increased physical activity to work effectively. The choice between them depends on your individual health profile and prescriber assessment — neither is inherently "better", but the dual mechanism of Mounjaro may suit some people differently than Wegovy's single GLP-1 pathway.
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.
Prescription Requirements and Access Routes
To access Mounjaro in the UK, you need a prescription from a licensed prescriber following a clinical assessment. This can happen through NHS specialist weight management services (tier 3 tier 4), where you'll be referred by your GP — though waiting lists vary significantly by region. Alternatively, private GPhC-registered online pharmacies offer Mounjaro prescriptions following an online consultation, usually within days rather than months. Your prescriber will assess your BMI, health conditions, medications, and suitability before issuing a prescription. Both access routes require the same clinical decision-making; the difference is speed and location. Regardless of route, you must have a valid UK prescription to legally obtain either medication.
- 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 without a prescription in the UK?
No. Mounjaro is prescription-only and controlled by the MHRA. You cannot purchase it over-the-counter or without a clinical assessment from a licensed UK prescriber. Any supply without a valid prescription is illegal.
Is Wegovy also prescription-only like Mounjaro?
Yes, Wegovy is also prescription-only in the UK. Both require a clinical assessment and a valid prescription. The main differences are the active ingredient (tirzepatide vs semaglutide), dosing schedule, and average weight loss in trials — not the prescription status.
Can my GP prescribe Mounjaro directly, or do I need a specialist?
Mounjaro is typically prescribed through NHS specialist weight management services (tier 3), not standard GP practice. However, some GPs may prescribe privately. For NHS access, you'll usually be referred to a specialist clinic. Private prescribers (online or in-person) can issue prescriptions without a specialist referral if you meet eligibility criteria.
How long does the prescription assessment take?
NHS assessments can take weeks to months depending on waiting lists in your region. Private online assessments typically take 24–48 hours, with prescription issued same-day or next-day if approved. Speed depends on your chosen route, not the medication itself.
What happens if I don't meet Mounjaro eligibility when assessed?
If you don't meet criteria for Mounjaro, your prescriber might suggest Wegovy, lifestyle support, or other approaches. Eligibility depends on BMI, health conditions, and individual factors. Your prescriber will explain alternatives based on your specific situation.
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.