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
What Does a Bubble in Your Mounjaro Pen Mean?
If you've noticed a small bubble or air pocket in your Mounjaro KwikPen, don't worry — this is completely normal and does not affect the medication. Mounjaro pens are manufactured with a small amount of air to protect the tirzepatide solution during storage and transport. Before injecting, you may see a bubble moving inside the pen, but this does not reduce the dose you receive. As long as your pen shows the correct dose number and hasn't been damaged or frozen, it's safe to use. If you have specific concerns about your individual pen, contact your pharmacist or GP for reassurance.
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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 — Key Differences Explained
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections available in the UK, but they work differently and show different results in clinical trials.
Mounjaro mechanism: Dual GIP and GLP-1 receptor agonist — activates two natural hormone pathways to help regulate appetite and blood sugar control.
Wegovy mechanism: GLP-1 receptor agonist only — works on a single pathway but is still highly effective.
Clinical trial results (SURMOUNT vs STEP): Mounjaro participants lost an average of 15–21% body weight at maximum dose over 72 weeks, whilst Wegovy participants lost approximately 15% over 68 weeks. However, individual results vary significantly, and what works best depends on your personal health profile, not the medication alone.
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.
Which Medication Is Right for You?
Neither Mounjaro nor Wegovy is automatically "better" — suitability depends on your individual health, medical history, and prescriber assessment. Both require a prescription from a UK-licensed healthcare professional following a clinical assessment to ensure they're safe and appropriate for you.
Access in the UK is through NHS specialist tier 3 weight management services (with potentially long waiting lists in many areas) or private online prescribing following a consultation. A prescriber will consider factors including your BMI, weight-related health conditions, current medications, and medical history before recommending either option. Use our free BMI calculator to understand your current weight category, and discuss prescription medication options with your GP or a licensed prescriber.
- 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 a bubble in a Mounjaro pen a sign the medication is damaged?
No. Small air bubbles in Mounjaro KwikPens are normal and intentional — they protect the solution during manufacturing and storage. As long as your pen hasn't been frozen, dropped, or left in extreme heat, it's safe to use. If you're concerned about a specific pen, ask your pharmacist to inspect it.
Should I try to remove the bubble from my Mounjaro pen before injecting?
No, do not attempt to remove bubbles or shake the pen vigorously. Simply hold the pen upright for a few seconds before injection. The bubble will not affect the dose delivered. The dose number on the pen is what you'll receive, regardless of any small air pockets.
How does Mounjaro's mechanism compare to Wegovy?
Mounjaro is a dual GIP+GLP-1 agonist (two pathways), whilst Wegovy is a GLP-1 agonist only (one pathway). Both are effective, but clinical trials suggest Mounjaro may achieve slightly higher average weight loss. However, individual responses vary — some people respond better to one than the other. Your prescriber will help decide which is more suitable.
Can I switch from Mounjaro to Wegovy if I'm not seeing results?
Switching between medications should only be done under prescriber guidance. They may adjust your Mounjaro dose first, as results improve gradually over weeks. Approximate dose equivalences exist, but any switch must be managed carefully by your healthcare provider to ensure continuity of treatment.
How do I access Mounjaro or Wegovy on the NHS in the UK?
Both medications are available through NHS specialist tier 3 weight management services, usually accessed via GP referral. However, availability and waiting times vary significantly by region. Your GP can advise on local services. Private online prescribing is also available if you meet eligibility criteria — a licensed prescriber will assess you following an online consultation.
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.