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
Mounjaro Starter Bundle vs Wegovy — Which is Right for You?
When considering weight management injections in the UK, many people ask whether Mounjaro or Wegovy is the better choice. Both are prescription-only medications licensed for weight management, but they work differently and have different starter dose schedules. This guide compares the two, covering their mechanisms, clinical trial data, and how to determine which might suit you — though your GP or prescriber will make the final assessment based on your individual health.
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 Mounjaro and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism may help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals.
Wegovy (semaglutide) is a single GLP-1 receptor agonist — it activates only the GLP-1 pathway. This also reduces appetite and supports satiety, though through one mechanism rather than two.
In clinical trials, Mounjaro showed slightly higher average weight loss than Wegovy: approximately 20.9% of body weight at the maximum dose of 15 mg (SURMOUNT-1 trial) compared to approximately 14.9% with Wegovy 2.4 mg (STEP-1 trial). However, individual results vary significantly, and both medications require a reduced-calorie diet and increased physical activity to be effective.
Both require a UK prescription following clinical assessment. Neither medication is a shortcut — they are tools used alongside lifestyle changes.
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.
Starter Bundles and Dose Titration Schedules
Mounjaro starter bundle: Begins at 2.5 mg once weekly for 4 weeks, then increases to 5 mg. Each KwikPen contains 4 doses (4 weeks supply).
Wegovy starter bundle: Begins at 0.25 mg once weekly for 4 weeks, then escalates through 0.5 mg, 1 mg, and 1.7 mg before reaching the maximum 2.4 mg dose. This takes longer to reach full dose.
Both follow a gradual dose titration to minimise side effects like nausea. Mounjaro reaches therapeutic doses faster, while Wegovy has a slower, more extended ramp-up. Your prescriber will choose based on your tolerance, health profile, and medical history. Neither offers a faster route to weight loss — both require patience and commitment to lifestyle changes.
- 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's the main difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP+GLP-1 receptor agonist (two hormone pathways), while Wegovy is a single GLP-1 agonist (one pathway). Clinical trials suggest Mounjaro may produce slightly higher average weight loss, but individual results vary significantly. Both require prescription and clinical assessment in the UK.
How do the starter bundles differ?
Mounjaro's starter bundle begins at 2.5 mg for 4 weeks before moving to 5 mg. Wegovy's starter is 0.25 mg, with a slower escalation over many weeks to reach 2.4 mg. Mounjaro reaches therapeutic doses faster, but neither offers a shortcut — both work alongside diet and exercise.
Which causes more side effects?
Both have similar common side effects (nausea, diarrhoea, constipation, stomach pain). Individual tolerance varies. Mounjaro's faster dose escalation may cause nausea initially, while Wegovy's slower titration might reduce early side effects. Your prescriber will choose based on your health and tolerance.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart — approximate equivalence exists (e.g., Mounjaro 10 mg ≈ Wegovy 1.7 mg), but any switch requires clinical supervision and dose adjustment.
Will the NHS prescribe either medication?
Both Mounjaro and Wegovy are available via NHS specialist tier 3 weight management services if you meet eligibility criteria (BMI ≥30, or ≥27 with weight-related conditions). Waiting lists vary by region. Private prescription through online clinics is also available without NHS referral.
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.