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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Understanding Bundle Switching in UK Weight Management
Bundle switching refers to changing between different weight loss injection medications or switching from one dose bundle to another as part of a structured weight management plan. In the UK, this often involves transitioning between GLP-1 medications like Mounjaro and Wegovy, or escalating doses within the same medication. This NHS health advice covers how bundle switching works, when it might be appropriate, and what to expect. Understanding your options supports informed conversations with your GP or prescriber about the best approach for your individual health needs.
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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.
How Bundle Switching Works in UK Weight Management
Bundle switching in UK weight management typically involves one of two scenarios: switching between different medications entirely, or progressing through dose escalations within the same medication.
Switching between medications: Your prescriber may recommend moving from one GLP-1 medication to another based on side effects, effectiveness, or your response. For example, if you experience persistent nausea on Wegovy, your prescriber might suggest Mounjaro instead. This requires a clinical assessment and a new prescription.
Dose escalation: Most weight loss injections use a step-up approach where you start on a lower dose for 4 weeks, then increase incrementally. Your prescriber bundles these dose increases based on your tolerance and weight loss progress. This is part of the standard treatment pathway, not a true "switch".
Important: Any bundle switching must be managed by your prescriber — never stop one medication and start another without clinical guidance.
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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
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Bundle Switching and UK Health Information
If you're considering bundle switching, discuss this with your GP or the prescriber managing your weight loss treatment. Factors that influence switching decisions include side effect profiles, cost, how your body responds, and your long-term weight management goals.
Key considerations:
- Side effect tolerance — if one medication causes persistent issues, an alternative may be better tolerated
- Weight loss progress — if you're not seeing expected results after adequate time on a dose, switching or increasing dose may be discussed
- Cost and NHS access — private prescription costs vary; your prescriber can advise on options
- Your overall health — any new health conditions or medications may affect which weight loss injection is most suitable
Our free weight converter and BMI calculator can help you track progress between bundle changes, providing useful health information to share with your healthcare team.
- 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 does bundle switching mean in weight loss treatment?
Bundle switching means changing between different weight loss medications (such as from Wegovy to Mounjaro) or progressing through planned dose increases within the same medication. It's part of UK health guidance for personalising weight management treatment to your individual response and needs.
Can I switch between Mounjaro and Wegovy bundles?
Yes, but only under prescriber guidance. Your GP or the prescriber managing your weight loss can assess whether switching is appropriate based on your side effects, progress, and health status. This requires a new clinical assessment and prescription — you shouldn't switch without clinical advice.
Is bundle switching available on the NHS?
NHS weight management services can arrange medication switches, though availability varies by region and ICB. Private prescribers offering weight loss injections can also facilitate switching following an online assessment and new prescription.
How does bundle switching affect cost in the UK?
Bundle costs vary depending on dose, medication, and provider. Switching to a different medication or dose may change your cost if using private prescriptions. Always ask your prescriber about cost implications before making any changes to your weight management plan.
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.