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
Free tracker included with every download this week
How Does the Mounjaro Pen Work Compared to Wegovy?
Mounjaro and Wegovy are both once-weekly injectable weight management medications, but they work in different ways. Mounjaro uses a dual mechanism — activating both GIP and GLP-1 hormone pathways — whilst Wegovy activates GLP-1 alone. Both come as pre-filled injection pens, but the doses, speed of titration, and clinical trial results differ. Understanding how each works can help you discuss options with your prescriber. This guide compares the mechanisms, eligibility, and practical use of both medications in the UK.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
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 the Dual Mechanism Works: Mounjaro vs Single-Action Wegovy
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist. This means it activates two natural hormone pathways simultaneously. GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1) both signal to your brain that you are full, slow how quickly food leaves your stomach, and regulate fat utilisation. The dual action may produce stronger appetite suppression than single-pathway medications.
Wegovy (semaglutide) activates GLP-1 alone. It signals fullness, slows gastric emptying, and reduces cravings — but via one hormone pathway rather than two. Clinical trials suggest both are effective, though individual results vary significantly. The dual mechanism of Mounjaro may explain why SURMOUNT trial participants lost an average of 15–21% body weight, compared to approximately 15% with Wegovy in STEP trials — though these are different studies with different populations.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Mounjaro KwikPen Doses vs Wegovy Pens: Titration and Maintenance
The Mounjaro KwikPen starts at 2.5 mg weekly and escalates every 4 weeks: 5 mg, 7.5 mg, 10 mg, 12.5 mg, and finally 15 mg maximum. Each pen contains 4 weeks of doses. Wegovy pens start lower (0.25 mg) and escalate more gradually over 16 weeks to reach 2.4 mg maximum. This slower titration with Wegovy may mean fewer gastrointestinal side effects initially, but it takes longer to reach the target dose. Both require a UK prescription and clinical assessment. Mounjaro NHS NICE guidance and private prescribing both require demonstrating eligibility — typically BMI 30+ or 27+ with weight-related health conditions. Your prescriber will discuss which escalation schedule suits you and monitor your response.
- 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 the same as Wegovy?
No. Both are once-weekly weight loss injections, but Mounjaro uses dual GIP/GLP-1 activation whilst Wegovy uses GLP-1 only. Mounjaro may produce stronger appetite suppression. Both require prescription and clinical assessment in the UK. Ask your prescriber which suits your health profile.
Does the Mounjaro KwikPen work differently than Wegovy?
Both are pre-filled injection pens you use yourself once weekly. The difference is in what they contain (the hormone mechanisms) not how you inject them. Storage, injection sites, and technique are similar. Mounjaro escalates faster (every 4 weeks) than Wegovy (every 4 weeks over 16 weeks total).
Can I switch from Wegovy to Mounjaro?
Possibly, but only with prescriber guidance. There is no official conversion chart — approximate equivalence exists (e.g. Wegovy 2.4 mg ≈ Mounjaro 15 mg) but switching requires clinical assessment. Your prescriber will manage the transition to minimise side effects.
Which loses more weight — Mounjaro or Wegovy?
In clinical trials, Mounjaro showed slightly higher average weight loss (15–21% vs ~15%), but results vary widely between individuals. Neither guarantees specific weight loss. Both work best alongside reduced-calorie diet and activity. Your prescriber will help choose the right option for you.
Does Mounjaro have more side effects because of the dual mechanism?
Both cause similar common side effects (nausea, diarrhoea, constipation). Mounjaro's stronger appetite suppression may mean more initial gastrointestinal effects. Most improve as your body adjusts. Report any concerns to your prescriber — dose adjustment or switching may help.
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.