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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Mounjaro vs Wegovy: Understanding the Differences
The term "clinically supported dose" is often used colloquially to describe the Mounjaro or Wegovy dose where users report optimal weight loss results with manageable side effects. Both medications are prescription-only injections licensed in the UK for weight management, but they work through different mechanisms and require different dosing schedules. Understanding how they compare can help you discuss options with your prescriber, though individual suitability is determined through clinical assessment.
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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 Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. This dual mechanism may contribute to its reported efficacy in clinical trials. Wegovy (semaglutide) activates only the GLP-1 pathway. In the SURMOUNT-1 clinical trial, Mounjaro at 15 mg achieved average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg achieved average weight loss of approximately 14.9% over 68 weeks. Both doses are maximum maintenance doses. Dosing schedules differ significantly: Mounjaro starts at 2.5 mg and escalates in 2.5 mg increments over 20+ weeks, with a maximum of 15 mg weekly. Wegovy starts at 0.25 mg and escalates in smaller increments, reaching 2.4 mg as the maintenance dose. Both are once-weekly injections. Individual results vary considerably, and weight loss depends on adherence, diet, and physical activity.
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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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Choosing Between Them: Clinical Assessment Matters
Neither medication is universally "better" — suitability depends on individual health factors, medical history, and prescriber judgment. Your GP or licensed prescriber will assess eligibility, current medications, and any contraindications. Both require a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. Both carry similar side effects including nausea, diarrhoea, and constipation, though severity varies. Private prescribers and NHS specialist weight management services both assess patients individually. If you're unsure which might be appropriate, use our free GLP-1 weight loss calculator to explore potential outcomes, then discuss findings with your prescriber during your consultation.
- 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 is the "clinically supported dose" of Mounjaro?
There is no official "clinically supported dose." The term refers colloquially to the dose where users perceive optimal weight loss with tolerable side effects, typically between 7.5 mg and 15 mg. However, the right dose for you is determined by your prescriber based on your response and tolerance. Some achieve good results at lower doses; others require the maximum 15 mg.
Is Mounjaro more effective than Wegovy?
Clinical trials show Mounjaro achieved higher average weight loss (approximately 21% at 15 mg) compared to Wegovy (approximately 15% at 2.4 mg). However, individual results vary significantly. Effectiveness depends on genetics, adherence, diet, exercise, and personal metabolism — not just the medication. Your prescriber can discuss which may suit your circumstances.
Can I switch from Wegovy to Mounjaro?
Switching between medications is possible but must be managed by your prescriber. There is no official dose conversion chart — approximate equivalence suggests Mounjaro 10 mg is roughly comparable to Wegovy 1.7 mg, but this is not an established clinical guideline. Your prescriber will advise on timing and dosing if a switch is appropriate.
Which injection is available on the NHS?
Both Mounjaro and Wegovy are NICE-approved and available through NHS specialist tier 3 weight management services. Availability, waiting times, and access criteria vary significantly by region. Your GP can refer you to your local specialist service. Private access to both is available through online prescribing without NHS referral.
Do Mounjaro and Wegovy have the same side effects?
Both share common side effects including nausea, diarrhoea, constipation, and stomach pain. Severity and frequency vary between individuals. Mounjaro's dual mechanism may cause slightly different tolerability patterns, but large-scale comparative data on side effect incidence is limited. Your prescriber will discuss likely effects based on your medical history.
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