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 Or Mounjaro — Which Is Better For You?
There isn't a straightforward answer to whether Wegovy or Mounjaro is "better" — both are prescription-only weight loss injections licensed in the UK, but they work differently and suit different people. Wegovy (semaglutide) uses a single GLP-1 mechanism, whilst Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist. Clinical trials show both help with weight loss on average, but individual results vary significantly. The right choice depends on your health profile, which a prescriber will assess during a clinical consultation. This guide compares them factually so you understand the key differences.
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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 They Work And Trial Results
Wegovy (semaglutide) is a GLP-1 receptor agonist — it activates one hormone pathway to reduce appetite, support feeling fuller, and slow stomach emptying. In the STEP-1 clinical trial, participants on the maximum 2.4 mg dose lost an average of approximately 14.9% of their body weight over 68 weeks alongside diet and exercise changes.
Mounjaro (tirzepatide) activates two pathways — both GIP and GLP-1 — which is a different mechanism. In the SURMOUNT-1 trial, the 15 mg dose showed average weight loss of approximately 20.9% of body weight. Clinical trials show Mounjaro achieved numerically higher average weight loss, but individual outcomes vary considerably.
- Wegovy: GLP-1 only, average ~clinically studied weight loss in trials
- Mounjaro: Dual GIP+GLP-1, average ~clinically studied weight loss in trials
- Both require reduced-calorie diet and increased activity for optimal results
- Both are prescription-only and require clinical assessment for eligibility
Trial results are averages — some people lose more, some lose less, and some don't respond as expected to either medication. Your prescriber will discuss realistic expectations during consultation.
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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 Which Might Suit You
Wegovy starts at 0.25 mg weekly and escalates to a maximum of 2.4 mg. Mounjaro starts at 2.5 mg and escalates to 15 mg. Both are injected once weekly. Common side effects are similar — nausea, diarrhoea, constipation, and stomach pain are most frequent with both medications. Injection site reactions occur with both.
Which suits you better depends on individual factors: your BMI, any weight-related health conditions, previous medication responses, tolerability, and prescriber assessment. Some people respond better to dual-mechanism (Mounjaro), others to single-mechanism (Wegovy). Neither is universally "better" — suitability is personal. A licensed prescriber will review your health history, current medications, and eligibility criteria to recommend which is appropriate for you. Try our GLP-1 weight loss calculator to explore projected outcomes, and use our free BMI calculator to understand your current weight category within NHS guidelines.
- 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 Mounjaro better than Wegovy because trial results were higher?
Clinical trials showed Mounjaro had numerically higher average weight loss, but this doesn't mean it's "better" for everyone. Individual results vary significantly with both medications. Some people respond excellently to Wegovy, others to Mounjaro. Trial averages don't predict individual outcomes. Your prescriber will assess which suits your health profile.
Can I switch from Wegovy to Mounjaro if Wegovy isn't working?
Potentially, yes — but only under prescriber guidance. There is no official conversion chart between the two, so any switch requires a new clinical assessment and prescription. Your prescriber will determine if switching is appropriate and what dose to start on. You cannot switch without professional supervision.
Which has fewer side effects, Wegovy or Mounjaro?
Both have similar common side effects — nausea, diarrhoea, and stomach discomfort are frequent with both. Individual tolerability varies. Some people tolerate one better than the other. Side effect severity often decreases over time as the body adjusts. Your prescriber can discuss tolerability profiles during consultation.
How long does it take to see weight loss results with either medication?
Weight loss typically becomes noticeable within 4–8 weeks, but the first few weeks focus on dose escalation and tolerating side effects. Most significant results appear after 12–16 weeks on a stable dose. Both medications require patience — rapid results aren't assured. Consistency with diet and exercise matters alongside medication.
Do I need an NHS referral to get Wegovy or Mounjaro privately in the UK?
No. You can access both through private online prescribing without an NHS referral. A UK-licensed prescriber will conduct an online clinical assessment. However, if you qualify for NHS access through a specialist tier 3 weight management service, your GP can refer you — though waiting lists vary by region and availability.
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.