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 Happens to Your Mounjaro Pen After 4 Doses?
After completing 4 doses of Mounjaro (tirzepatide), you'll have finished one KwikPen device, which contains exactly 4 weeks' supply at your current dose level. At this stage, you'll need to arrange your next prescription to continue treatment. Whether you access Mounjaro through NHS specialist services or privately, understanding the renewal process, costs, and dose progression is essential for uninterrupted treatment.
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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.
UK Private Prescription Costs and Access After Initial Doses
Once you've completed your initial 4-dose KwikPen, the cost of continuing Mounjaro privately in the UK typically ranges from £129 to £320 per month, depending on your current dose level. Higher doses (10mg and 15mg) cost more than starter doses (2.5mg and 5mg). After 4 weeks, you'll usually be ready for a dose increase — your prescriber will review your progress and tolerability before escalating to the next level as part of the standard tirzepatide dose titration schedule. Many online prescription services offer subscription models where your next pen is automatically dispatched, or you can request a new prescription each month. Each new KwikPen device contains 4 pre-filled doses, so you'll need a fresh pen monthly. Private prescriptions require an online clinical reassessment, though this is often streamlined for existing patients. NHS access, where available through tier 3 specialist weight management services, does not involve direct costs to the patient, but availability and waiting times vary significantly across regions and ICBs.
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.
NHS vs Private Routes: Continuing Treatment After Initial Doses
If you've been prescribed Mounjaro through the NHS, your specialist service will manage dose progression and supply directly — there are no out-of-pocket costs. However, NHS access typically requires referral through your GP to a tier 3 weight management service, and waiting lists can be lengthy. Private access allows you to continue immediately without NHS referral but requires a valid UK prescription from a licensed prescriber following an online clinical assessment. Both routes assess your eligibility based on BMI (30 or above, or 27+ with weight-related health conditions), individual health factors, and medication tolerability. You can track your progress using a free BMI calculator and our GLP-1 weight loss projection calculator to estimate potential outcomes at your current and future doses based on clinical trial data.
- 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.
Why does a Mounjaro KwikPen only contain 4 doses?
Each KwikPen is designed for exactly 4 weeks of once-weekly injections. This aligns with the standard dose titration protocol, where you remain on each dose level for a minimum of 4 weeks before escalating. After 4 weeks, you'll typically progress to the next dose and require a new pen.
How much does a second Mounjaro pen cost in the UK privately?
Private costs typically range from £129 to £320 per month depending on your dose. Starter doses (2.5mg–5mg) cost less; higher maintenance doses (10mg–15mg) cost more. Some providers offer subscription discounts or payment plans.
Can I get a second Mounjaro prescription without seeing my GP again?
No — you'll need a new prescription from a UK-licensed prescriber for each subsequent pen. Private online prescribers offer streamlined reassessments for existing patients, which are faster than initial consultations. NHS patients continue through their specialist service with no additional GP involvement.
What's the difference between Mounjaro and Wegovy for cost and access?
Mounjaro (tirzepatide) typically costs £180–£320/month privately; Wegovy (semaglutide) usually costs £129–£250/month. Both require prescriptions and clinical assessment. Mounjaro uses a dual GIP+GLP-1 mechanism with higher average weight loss in trials; Wegovy uses a single GLP-1 mechanism. NHS availability varies by region for both.
Will my NHS prescription continue automatically after 4 doses?
Yes — if you're prescribed through NHS tier 3 services, your specialist team will manage ongoing supply and dose escalation. You won't need to reapply; your care is continuous as long as you continue meeting eligibility criteria and responding well to 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.