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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How Quickly Do You Lose Weight With Mounjaro vs Wegovy?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription weight loss injections available in the UK, but they work at different speeds. Clinical trials show Mounjaro tends to produce faster initial weight loss than Wegovy, though individual results vary significantly. This comparison breaks down the trial data, dosing schedules, and what realistic timescales look like for weight loss with each medication. Weight loss typically begins within the first 2–4 weeks, with the most significant losses occurring between weeks 8–16.
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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 Weight Loss Data — Mounjaro vs Wegovy
The most significant clinical evidence comes from the SURMOUNT-1 trial for Mounjaro and the STEP-1 trial for Wegovy. Mounjaro at the maximum dose (15 mg weekly) showed an average weight loss of approximately 20.9% of body weight over 72 weeks, compared to Wegovy at 2.4 mg (the maximum weight loss injection uk dose) which achieved approximately clinically studied weight loss over 68 weeks. This difference reflects Mounjaro's dual GIP + GLP-1 mechanism versus Wegovy's single GLP-1 action. However, results vary substantially between individuals — some lose more, some less. Both medications show gradual, steady weight loss rather than rapid drops. The weekly weight loss injection schedule means dose increases occur every 4 weeks (Mounjaro) or over 16 weeks (Wegovy), with the most noticeable effects appearing after reaching maintenance doses. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses based on your current weight.
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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.
Weight Loss Timeline — What to Expect in the First Months
Most people begin noticing weight loss within 2–4 weeks of starting either medication, though initial losses are often modest — typically 1–3 kg in the first month. Between weeks 4–12, weight loss accelerates as your dose increases and your body adapts to the medication. By week 12–16, many people report more significant losses of 5–10 kg or more. The mounjaro kwikpen and Wegovy pre-filled pens both require a mounjaro uk prescription and dose titration schedule lasting 16+ weeks to reach maximum effect. Weight loss continues steadily through weeks 16–24, then typically plateaus. Importantly, prescription weight loss uk treatment works alongside dietary changes and increased activity — medication alone without lifestyle changes produces minimal results. Your GP or prescriber will advise on realistic expectations based on your individual health, BMI, and medical history.
- 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.
Does Mounjaro cause faster weight loss than Wegovy?
Clinical trial data suggests Mounjaro may produce slightly faster average weight loss — 20.9% versus 14.9% with Wegovy. However, individual results vary considerably. Some people lose weight faster on Wegovy; others respond better to Mounjaro. Your prescriber will assess which suits you based on your health history and mounjaro nhs nice eligibility.
How much weight can you lose in the first month on Mounjaro?
Most people lose 1–3 kg in the first month on Mounjaro, though some lose more or less. Initial losses are often modest because the starting dose (2.5 mg) is low. Weight loss accelerates as your dose increases over the first 16 weeks and your body adapts to the medication.
What's the difference between Mounjaro and Wegovy mechanisms?
Mounjaro is a dual GIP + GLP-1 receptor agonist — it activates two hormone pathways. Wegovy is a GLP-1 agonist only, activating one pathway. This dual action may explain why Mounjaro users report slightly faster average weight loss, though both require clinical assessment and prescription.
How long does the mounjaro dose titration take?
Mounjaro dose titration takes approximately 16–20 weeks to reach the maximum 15 mg dose. You start at 2.5 mg and increase by 2.5 mg every 4 weeks. Each step takes effect gradually, with noticeable weight loss changes occurring weeks 4–12 as doses increase.
Can I track my weight loss progress with MyWeightCheck?
Yes. Use our free progress tracker on this page to log your weekly weight and track your journey visually. Combined with our BMI calculator and weight converter, you can monitor your progress in stone, kilograms, or pounds — whatever measurement you prefer.
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.