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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Starting Mounjaro: Your First Day Guide in the UK
Starting Mounjaro involves more than just your first injection — it's about understanding how to access the medication, what to expect, and the costs involved. Whether you're considering the NHS route or private prescription access, this guide covers everything you need to know about beginning tirzepatide treatment in the UK. Your first day preparation starts long before the injection itself.
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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.
How to Access Mounjaro in the UK
There are two main routes to access Mounjaro in the UK: through the NHS or via private prescription.
NHS access: NICE has approved tirzepatide (Mounjaro) for use in specialist tier 3 and tier 4 weight management services. You'll need a referral from your GP to a specialist weight management service in your area. NHS availability varies significantly by region — some areas have dedicated services while others have long waiting lists lasting many months. Your GP can advise whether your local ICB (Integrated Care Board) funds Mounjaro access.
Private access: You can access Mounjaro privately through a GPhC-registered online pharmacy following an online clinical assessment with a UK-licensed prescriber. This route doesn't require an NHS referral and prescription can be issued within 24–48 hours if you're deemed clinically suitable. Private access is typically faster but involves upfront costs.
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.
What Your First Day Involves & Cost Context
Before your first injection, you'll have a clinical assessment to check your eligibility — BMI, weight-related health conditions, and suitability. Your first Mounjaro dose is always 2.5 mg, regardless of route.
Private costs: Mounjaro typically costs £129–£200 per month at starting dose (2.5 mg), rising to £200–£320 at higher maintenance doses, depending on the prescriber. This includes the prescription assessment. You'll receive a KwikPen containing four weeks of injections.
On your actual first day, you'll self-inject subcutaneously (under the skin) in the stomach, thigh, or upper arm. Store your unused pens in the fridge at 2–8°C. After your first injection, nausea is common but typically mild at the starting dose. Keep taking your regular medications unless advised otherwise.
- 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 much does Mounjaro cost on the NHS?
NHS prescriptions are free once dispensed, but access is limited to specialist weight management services. Availability and waiting times vary greatly by region. Contact your GP about your local ICB's commissioning arrangements and whether Mounjaro is funded in your area.
Can I get Mounjaro privately without seeing my GP first?
Yes. You can access Mounjaro via a private online consultation with a UK-licensed prescriber without an NHS referral. The prescriber will assess your eligibility during the online appointment and issue a prescription if appropriate.
What should I do before my first Mounjaro injection?
Before injecting, ensure your KwikPen has been stored at 2–8°C (never frozen). Check the expiry date. Rotate your injection site weekly. Have food available after injection in case of nausea. If you're on oral contraceptives, switch to a barrier method for 4 weeks. Inform your prescriber of all other medications.
How long does Mounjaro access take on the NHS vs private?
NHS access requires a GP referral and specialist assessment, typically taking 3–12 months depending on your region's waiting list. Private access is usually faster — clinical assessment to prescription in 24–48 hours if approved, with medication arriving within 2–5 working days.
Is private Mounjaro more expensive than NHS?
Private Mounjaro involves upfront monthly costs (£129–£320 depending on dose). NHS is free at point of dispensing once accessed, but requires specialist referral and may involve months of waiting. Cost-benefit depends on your circumstances and how quickly you need to start treatment.
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.