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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Switching Mounjaro Providers in the UK
If you're currently taking Mounjaro (tirzepatide) and considering switching providers or medications, it's important to understand your options and how to do this safely. In the UK, you can access Mounjaro through NHS specialist weight management services or private online prescribing following clinical assessment. This guide explains switching between providers, comparing Mounjaro with alternatives like Wegovy (semaglutide), and what happens to your treatment when you make a change. Always discuss any switch with your current prescriber or GP first.
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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.
Mounjaro vs Wegovy — Key Differences When Switching
Both Mounjaro and Wegovy are prescription-only weight management injections available in the UK, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, activating two hormone pathways to help regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1 receptor agonist only, working through a single mechanism.
Clinical trial data shows important differences: SURMOUNT-1 trials of Mounjaro showed average weight loss of approximately 15–21% body weight at maximum dose (15mg weekly), whilst STEP trials of Wegovy showed approximately 15% average weight loss at maximum dose (2.4mg weekly). However, individual results vary significantly based on genetics, lifestyle, and how your body responds to each medication.
Switching between them requires a new clinical assessment and prescription from your provider. Your prescriber will consider which is more suitable based on your health profile, previous response, and side effect tolerance.
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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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Switching Providers — NHS vs Private Options
In the UK, you can access Mounjaro through two main pathways: NHS specialist tier 3 weight management services (usually requiring GP referral with potential waiting lists) or private online prescribing (available directly following an online assessment with a UK-licensed prescriber).
If you're switching between NHS and private providers, ensure continuity by discussing your current dose, start date, and any side effects you've experienced. Private prescribers can access your NHS records if you authorise it. If switching private providers, request a copy of your prescription history and current dose details. Never stop Mounjaro abruptly — your new provider should plan a handover. Allow 2–4 weeks between applications to ensure uninterrupted supply, as processing times vary.
- 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.
Can I switch from Mounjaro to Wegovy on the NHS?
Potentially, yes. Both are available through NHS tier 3 specialist weight management services, though availability varies by region (ICB). If you've been on Mounjaro with good results, your NHS specialist may recommend continuing rather than switching. If side effects are problematic, they may assess Wegovy as an alternative. Request a specialist review to discuss your options.
Do I need a new clinical assessment to switch providers?
Yes. Any change of provider (NHS to private, or between private providers) requires a new clinical assessment. Your new prescriber will review your medical history, current health, and suitability for continued treatment. This protects your safety and ensures the prescriber is confident in treating you.
What happens to my Mounjaro KwikPen if I switch?
Do not use expired or opened pens beyond 30 days. Unopened pens can be stored in the fridge (2–8°C) for months until the expiry date. If switching providers, coordinate the changeover so your new provider's first pen arrives before your current supply runs out. Do not discard unused pens; ask your pharmacy about disposal.
Will switching Mounjaro doses affect my weight loss progress?
Switching providers should not affect your dose if you transfer at the same tirzepatide level. However, if you switch to Wegovy or change doses, your results may vary as you adjust. Individual responses differ significantly. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses and share projections with your new prescriber.
Can I get Mounjaro via NHS if I was previously on private Mounjaro?
Potentially, yes, but NHS access depends on regional availability and meeting eligibility criteria (BMI ≥30, or BMI ≥27 with weight-related health conditions). Private treatment history alone doesn't assures NHS access. Request a GP referral to your local tier 3 weight management service to explore NHS options. Waiting lists vary by region. ```
Ready to take control of your weight loss journey?
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