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 Each Dose?
Each Mounjaro KwikPen contains four pre-filled doses, with a new pen required every four weeks. Understanding what happens after each injection — including pen disposal, storage, and the costs involved — helps you plan your treatment. In the UK, you can access tirzepatide (Mounjaro) through NHS specialist weight management services or private prescription routes, each with different cost and timeline implications.
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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.
Mounjaro Pen Reusability and Disposal After Each Dose
After each weekly injection, your Mounjaro KwikPen is not disposable — the same pen is reused for all four doses over four weeks. Only after the fourth and final dose is the pen discarded. Each pre-filled pen holds exactly four weeks of treatment at a fixed dose.
- Each injection: You inject once weekly from the same pen
- Four doses per pen: The pen lasts exactly 28 days
- After week 4: Dispose of the empty pen safely in a sharps bin or return it to a pharmacy
- Needle disposal: Never reuse needles — each injection requires a new needle (included with each pen)
- Storage between doses: Keep the pen in the fridge between injections (2–8°C) if unopened; after first use, it can be kept at room temperature (below 30°C) for up to 30 days
This differs from some other GLP-1 medications like Saxenda (liraglutide), which comes as a multi-use pen that lasts longer. Mounjaro's once-weekly dosing and four-dose-per-pen design simplifies your weekly routine.
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.
Mounjaro Cost and UK Access: NHS vs Private Routes
NHS access: Mounjaro is available through NHS specialist tier 3 weight management services, though regional availability varies significantly. NHS referral is free, but waiting times can be substantial in many areas — sometimes 6–12+ months depending on your ICB (Integrated Care Board). Your GP can refer you if you meet NICE eligibility criteria (BMI ≥30, or ≥27.5 with weight-related health conditions).
Private prescription: Private online consultations with UK-licensed prescribers offer faster access. Following a clinical assessment, prescriptions are dispensed by GPhC-registered pharmacies. Private costs typically range from £129–£320 per month depending on your dose — higher doses incur higher costs. This route bypasses NHS waiting lists but requires upfront payment. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses, helping you make an informed decision.
Understanding the full cost picture helps you choose the right access route. Both NHS and private routes require you to meet clinical eligibility criteria and undergo an assessment. Your prescriber will confirm which dose you begin on (typically 2.5 mg) and discuss how you'll progress through dose titration over several months. Track your progress with our free progress tracker once you start treatment.
- 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 reuse my Mounjaro KwikPen after each injection?
No. While the same pen is used for all four weekly injections, the entire pen is discarded after the fourth dose. You cannot reuse it beyond the four pre-filled doses it contains. You'll receive a new pen every four weeks.
How much does Mounjaro cost in the UK?
Through the NHS, Mounjaro is free once prescribed by a specialist weight management service, though waiting times vary by region. Privately, costs typically range from £129–£320 per month depending on your dose. Higher doses (e.g. 15 mg) cost more than lower doses (e.g. 2.5 mg).
What's the difference between Mounjaro and Wegovy in terms of access?
Both are once-weekly injections requiring prescription. Mounjaro is a dual GIP/GLP-1 agonist; Wegovy is GLP-1 only. Access routes are identical — NHS specialist services or private prescription. Clinical trial data shows Mounjaro achieved slightly higher average weight loss (~20.9% at 15 mg) compared to Wegovy (~14.9%), though individual results vary.
Do I need a GP referral to access Mounjaro privately?
No. Private online prescribing does not require a GP referral. You can contact a GPhC-registered online prescriber directly, complete a clinical assessment, and receive a prescription if deemed suitable. NHS access does require a GP referral to specialist weight management services.
How long does one Mounjaro pen last?
One KwikPen contains four pre-filled doses and lasts exactly four weeks (28 days) when injected once weekly. After your fourth injection, the pen is discarded and you receive a new one. This continues throughout your treatment as you progress through dose titration.
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.