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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Wegovy 1mg vs Mounjaro — How Do They Compare?
If you're considering weight management injections in the UK, you may be comparing 1mg Wegovy to Mounjaro. Both are prescription-only GLP-1 and GIP receptor agonists licensed for adults with excess weight, but they work differently and have different dosing schedules. Understanding the differences can help you and your prescriber decide which might be right for you. This guide compares the two based on clinical trial data, mechanism of action, and UK eligibility criteria.
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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.
Clinical Trial Data and Mechanism Differences
Wegovy (semaglutide) is a GLP-1 receptor agonist only. In the STEP-1 clinical trial, participants on 2.4mg (the maximum dose) achieved an average weight loss of approximately 14.9% of body weight over 68 weeks, alongside a reduced-calorie diet and physical activity.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. In the SURMOUNT-1 trial, participants on 15mg (the maximum dose) achieved an average weight loss of approximately 20.9% of body weight over 72 weeks, also alongside lifestyle changes.
The key difference is mechanism: Wegovy targets GLP-1 alone, while Mounjaro targets both GIP and GLP-1. This dual action in Mounjaro may contribute to potentially greater average weight loss in clinical trials, though individual results vary significantly.
At 1mg, Wegovy is in the early escalation phase (typically weeks 5–8 of treatment), not the maintenance dose. Direct comparison at this dose to full-strength Mounjaro is not clinically standard, as doses are escalated gradually over weeks based on tolerability and response.
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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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Dosing, Eligibility, and What Comes Next
Both medications are prescription-only in the UK and require a clinical assessment before being prescribed. Eligibility typically includes a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease.
Wegovy is escalated from 0.25mg to a maximum of 2.4mg over approximately 16 weeks. At 1mg, you're mid-way through the escalation phase. Mounjaro is escalated from 2.5mg to a maximum of 15mg over approximately 20 weeks. Neither medication is stopped at an intermediate dose — doses continue to increase as tolerated unless side effects occur.
Your GP or prescriber will assess your individual health, medical history, and preference to determine which medication is most suitable. Neither is inherently "better" — suitability depends on your personal circumstances. Use our GLP-1 weight loss calculator to estimate potential weight loss at different doses, and our BMI calculator to understand your current health status context.
- 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.
Is Wegovy 1mg equivalent to Mounjaro?
No. Wegovy 1mg is an intermediate dose during escalation (typically weeks 9–12), not a maintenance dose. Mounjaro starts at 2.5mg and escalates up to 15mg. They are not directly equivalent — they use different mechanisms and dosing schedules. Approximate clinical equivalence is estimated at: Wegovy 0.5mg ≈ Mounjaro 5mg, and Wegovy 2.4mg ≈ Mounjaro 15mg, but any dose change must be managed by your prescriber.
Which caused more weight loss in clinical trials — Wegovy or Mounjaro?
In published trials, Mounjaro (20.9% average weight loss at maximum dose) showed numerically higher average weight loss than Wegovy (14.9% at maximum dose). However, both were tested alongside reduced-calorie diet and physical activity, and individual results vary considerably. Trial results do not predict personal outcomes. Your prescriber will discuss realistic expectations.
Can I switch from Wegovy to Mounjaro on the NHS in the UK?
NHS access to both medications is through tier 3 specialist weight management services following referral from your GP. Switching between medications is possible but requires prescriber approval and assessment. Availability varies significantly by region (ICB). Ask your GP about local specialist services or contact your local ICB for referral pathways.
What are the main side effects at Wegovy 1mg compared to Mounjaro?
At 1mg, Wegovy commonly causes nausea, diarrhoea, vomiting, and constipation — similar to Mounjaro at lower doses. Both have the same side effect profile because they're both GLP-1 receptor agonists (or GLP-1-containing in Mounjaro's case). Side effects often reduce as the body adjusts over 2–4 weeks. Report persistent or severe effects to your prescriber.
How do I decide between Wegovy and Mounjaro?
This is a clinical decision made with your GP or prescriber. Factors include: your BMI and health conditions, tolerability of side effects, previous medication responses, cost (private vs NHS access), and prescriber experience. Both are licensed in the UK for eligible adults. Your prescriber will assess which is most suitable based on your individual circumstances. Neither medication is suitable without clinical assessment.
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