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
How to Change Your Mounjaro Supplier in the UK
If you're currently taking Mounjaro (tirzepatide) and need to change where you get your prescription filled, there are important steps to follow depending on whether you access it through the NHS or privately. Understanding your options and how to manage the transition safely ensures you don't miss doses and continue your weight management journey without disruption. This guide covers both NHS and private routes in the UK.
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.
Changing Mounjaro Supplier: NHS vs Private Routes
Your route to changing suppliers depends on how you currently access Mounjaro. If you receive Mounjaro through NHS tier 3 specialist weight management services, you cannot simply switch providers yourself — you'll need to contact your current NHS service and request a transfer or referral. NHS services are regional, and moving to a different area may require referral to a new local integrated care board (ICB) weight management service. If you obtain Mounjaro privately, you have more flexibility — you can switch to a different GPhC-registered online pharmacy or prescriber at any time. Both routes require careful timing to avoid gaps in your treatment. Before switching, ensure you have enough Mounjaro KwikPens to cover the transition period, as supply delays can happen. A standard KwikPen contains 4 weeks of doses, so plan ahead. If you're considering switching because of cost, side effects, or eligibility concerns, discuss this with your prescriber or GP first, as they may suggest alternatives like adjusting your dose or exploring different weight loss medications such as Wegovy (semaglutide) or other GLP-1 receptor agonists.
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.
Practical Steps for Switching Mounjaro Suppliers
For NHS patients: Contact your weight management service to request a transfer. If you're moving house or changing GP, notify your current service immediately and ask about referral to a new local NHS provider. This process can take several weeks, so request the transfer well in advance. For private patients: Once you have a new prescription from your new prescriber, contact your new pharmacy with your prescription details. Stop ordering from your previous supplier. Keep a note of when you last received a KwikPen and plan your new order to arrive before you run out. Important safety point: Never stop Mounjaro abruptly without medical guidance. If there's any gap in supply, speak to your prescriber about bridging options. Your GP can also provide temporary support if needed. Keep records of your current dose, injection sites, and any side effects to share with your new prescriber, as this helps them manage your care continuity effectively.
- 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 NHS Mounjaro to private supply?
Yes. You can request to stop NHS treatment and arrange private supply instead. Inform your NHS weight management service in writing, then contact a private prescriber or online pharmacy. Ensure you have Mounjaro in hand before you stop NHS supply to avoid gaps. Your GP can support the transition.
What if I'm moving to a different region and my NHS service changes?
Contact your current weight management service immediately and request a referral to your new local NHS ICB service. Provide your current dose, start date, and any relevant medical history. The transition can take 4–8 weeks, so request it early and ask about bridging supply if needed.
Is Mounjaro supply assured if I switch suppliers?
Private suppliers generally have more stock availability than NHS services, but shortages can still occur. Confirm availability with your new supplier before stopping your current one. For NHS, supply is managed regionally and may have waiting lists depending on your ICB.
If I switch suppliers, will my dose change?
Your dose should remain the same unless your new prescriber recommends a change after clinical review. Always bring records of your current dose and any side effects to your new prescriber to ensure continuity of care.
Can I switch from Mounjaro to Wegovy with the same supplier?
If using a private prescriber or online service, yes — many providers offer both tirzepatide and semaglutide-based weight loss options. A clinical assessment will determine which is more suitable for you. NHS switching requires new referral to specialist services.
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.