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 Many Doses Are In A Mounjaro Pen?
Each Mounjaro KwikPen contains exactly 4 doses — enough for 4 weeks of once-weekly injections. This is different from Wegovy, which is also a once-weekly injection but comes in a different pen format. Understanding your medication's dosing schedule helps you manage your treatment properly and plan your prescription refills. Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work slightly differently and come in different delivery systems.
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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.
Mounjaro vs Wegovy: Doses, Pens, And Mechanisms
Mounjaro (tirzepatide) is supplied as a KwikPen pre-filled auto-injection device. Each pen contains 4 doses and covers 4 weeks of treatment. Doses range from 2.5 mg (starting) up to 15 mg (maximum), with typical escalation every 4 weeks: 2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg. Each pen is single-use after 4 weeks.
Wegovy (semaglutide) is also a once-weekly injection but uses a different pen design. It comes in doses of 0.25 mg, 0.5 mg, 1 mg, 1.7 mg, and 2.4 mg (maximum), with a similar 4-week escalation schedule. The key difference is that Mounjaro is a dual GIP and GLP-1 receptor agonist, while Wegovy is a GLP-1-only medication. Clinical trial data (SURMOUNT for Mounjaro, STEP for Wegovy) showed both can help achieve meaningful weight loss when combined with dietary and lifestyle changes, though individual results vary significantly.
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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.
Choosing Between Mounjaro And Wegovy In The UK
Both Mounjaro and Wegovy are prescription-only and require a clinical assessment before being prescribed. Your prescriber will consider your medical history, current health conditions, other medications, and individual suitability when deciding which is appropriate for you. Neither medication is assured to work for everyone — response varies based on many factors including your starting weight, lifestyle changes, and how your body responds to the medication. Both are available through NHS specialist tier 3 weight management services or private online prescribing following a consultation. Try our GLP-1 weight loss calculator to understand projected outcomes at different doses, and use our BMI calculator to assess your current health status in line with 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.
How many doses does one Mounjaro KwikPen contain?
One Mounjaro KwikPen contains exactly 4 pre-filled doses, each for a once-weekly injection. After 4 weeks, you dispose of the pen and receive a new one. Each dose may be at the same strength or a higher strength depending on your dose escalation schedule.
What's the difference between Mounjaro and Wegovy pens?
Both contain once-weekly injections, but Mounjaro is a dual GIP+GLP-1 agonist and Wegovy is GLP-1-only. Mounjaro doses range up to 15 mg weekly; Wegovy up to 2.4 mg weekly. Both pens are pre-filled and single-use after 4 weeks. Clinical trials (SURMOUNT vs STEP) showed different average weight loss outcomes, though individual results vary.
How do I know which dose I should be on?
Your prescriber determines your dose based on your health assessment, medical history, and response to treatment. Both medications start at lower doses and escalate every 4 weeks if tolerated. You should never adjust your dose without consulting your prescriber.
Can I switch from Mounjaro to Wegovy?
Any switch between medications must be managed by your prescriber. While approximate dose equivalences exist (5 mg Mounjaro ≈ 0.5 mg Wegovy), there is no official conversion chart. Your prescriber will assess whether a switch is clinically appropriate and how to manage the transition safely.
Where can I get Mounjaro or Wegovy in the UK?
Both are available through NHS specialist tier 3 weight management services (referral via GP) or private online prescribing following a clinical assessment with a UK-licensed prescriber. NHS access varies by region and wait times can be lengthy. Private prescribing is available without NHS referral through GPhC-registered pharmacies.
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.