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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Will My Doctor Prescribe Mounjaro? Mounjaro vs Wegovy Explained
Whether your GP will prescribe Mounjaro depends on your individual health profile, BMI, and any weight-related health conditions you have. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and may suit different people. This guide explains the key differences so you can understand what to expect when discussing options with your GP or a licensed prescriber. Use our free BMI calculator above to check your starting point before any consultation.
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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 and Wegovy Differ: Clinical Trial Evidence
The main difference between Mounjaro and Wegovy is their mechanism of action. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways to regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1-only agonist, activating a single pathway. In clinical trials, this difference showed in outcomes:
- Mounjaro (SURMOUNT trial): participants lost an average of 15–21% of body weight at the highest dose (15 mg)
- Wegovy (STEP trial): participants lost an average of 14.9% of body weight at the highest dose (2.4 mg)
However, individual results vary significantly, and the difference between the two may not be significant for every person. Both require a reduced-calorie diet and increased physical activity to achieve results. A prescriber will assess which medication, if either, suits your individual circumstances.
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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.
Will Your GP Prescribe Either? Eligibility and Prescriber Decision
Your GP may prescribe either Mounjaro or Wegovy if you meet UK eligibility criteria: a BMI of 30 or above, or BMI of 27–29.9 with at least one weight-related health condition (such as type 2 diabetes, high blood pressure, or sleep apnoea). For South Asian, Chinese, Black African, or Black Caribbean adults, lower thresholds may apply. However, prescriber choice depends on factors including your medical history, previous weight loss attempts, and individual response to similar medications. Neither medication is assured — a clinical assessment is always required. You can check your BMI using our weight converter and free BMI calculator to understand where you stand before your appointment.
- 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 my GP prescribe Mounjaro, or do I need to go private?
Your GP can refer you to a specialist NHS tier 3 weight management service, where Mounjaro may be prescribed following NICE approval. However, NHS availability varies by region and waiting lists can be lengthy. Private online prescribing is also available through UK-licensed prescribers if you prefer faster access and don't require NHS referral.
Is Mounjaro stronger than Wegovy?
Clinical trials suggest Mounjaro may result in slightly higher average weight loss (15–21% vs 14.9%), but the difference is modest and individual results vary considerably. "Stronger" depends on how each medication works for your body. A prescriber will assess which suits you best.
What's the difference between the Mounjaro KwikPen and Wegovy pen?
Mounjaro uses a KwikPen (once weekly, doses up to 15 mg) while Wegovy uses an auto-injection pen (once weekly, maximum 2.4 mg). Both are pre-filled and designed for self-injection. The main difference is the medication itself, not the delivery device.
Will my GP discuss both Mounjaro and Wegovy with me?
A good prescriber will discuss available options relevant to your health profile. Both are licensed for weight management in the UK, but prescriber choice may depend on your medical history, previous medication responses, and individual circumstances. You can ask about both during your consultation.
What happens if Mounjaro doesn't work for me — can I switch to Wegovy?
Yes, if Mounjaro doesn't produce results or causes side effects you can't tolerate, a prescriber may suggest switching to Wegovy or another option. Any switch should be managed by your prescriber to ensure safe transition. This is another reason to discuss goals and expectations clearly at the start.
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.