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 Does the Mounjaro Pen Work? UK Cost & Access Guide
The Mounjaro KwikPen is a pre-filled injection device that delivers tirzepatide, a dual GIP and GLP-1 receptor agonist medication for weight management. Each pen contains four weekly doses and is injected once per week under the skin. Understanding how the pen works, alongside UK pricing and how to access it through NHS or private routes, helps you make an informed decision about whether this treatment might suit your health needs. This guide covers the mechanism, costs, and access pathways available to UK adults.
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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 KwikPen Costs by Dose in the UK
Private prescription costs vary by provider and dose strength:
- 2.5 mg dose: approximately £129–£159 per pen (4 weeks)
- 5 mg dose: approximately £149–£179 per pen
- 7.5 mg dose: approximately £169–£199 per pen
- 10 mg dose: approximately £189–£219 per pen
- 12.5 mg dose: approximately £209–£239 per pen
- 15 mg dose: approximately £229–£259 per pen
These are typical private pharmacy ranges as of 2026. Costs may vary depending on the online prescriber and pharmacy used. Most private providers offer subscription or per-dose purchase options. Many people require dose titration over 20 weeks before reaching their maintenance dose, so total initial cost depends on your starting point and escalation schedule.
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 Access Routes in the UK
NHS route: Mounjaro is available through NHS specialist weight management services (tier 3/4) following NICE approval for tirzepatide. Access requires a GP referral to your local Integrated Care Board's specialist service. Eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related comorbidities. NHS waiting lists vary significantly by region — some areas have waiting times of several months or longer. Once approved, the NHS covers prescription costs.
Private route: Available through GPhC-registered online pharmacies following an online clinical assessment with a UK-licensed prescriber. No NHS referral needed. Prescriptions are issued if clinically appropriate. Private access is faster than NHS routes but costs are patient-funded. This mounjaro uk prescription route allows immediate access without waiting lists.
- 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 do you use the Mounjaro KwikPen?
Remove the pen from the fridge 15 minutes before use. Check the clear liquid in the window. Pinch the skin on your stomach, thigh, or upper arm. Insert the needle at 90 degrees and hold for 3 seconds after hearing two clicks. Store the used pen at room temperature for up to 30 days, then dispose safely.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro uses once-weekly doses up to 15 mg; Wegovy goes up to 2.4 mg. Clinical trials showed Mounjaro produced slightly higher average weight loss, but individual results vary. Both are prescription-only and available via NHS specialist services or private prescribing.
Am I eligible for Mounjaro on the NHS?
You may be eligible if you have a BMI of 30 or above, or 27–29.9 with weight-related conditions like type 2 diabetes, hypertension, or sleep apnoea. For South Asian, Chinese, Black African, or Black Caribbean adults, lower BMI thresholds may apply. Ask your GP about referral to your local specialist weight management service. Mounjaro nhs nice approval means it's available, but access varies by region.
What are the main side effects I should expect?
Very common side effects include nausea, diarrhoea, vomiting, and constipation, especially during dose escalation. These often improve over time. Less common are headache, fatigue, and injection site reactions. Serious side effects are rare but include severe stomach pain (possible pancreatitis) or allergic reactions. Discuss mounjaro side effects uk concerns with your prescriber before starting.
How long does it take to see weight loss results?
Weight loss typically begins within the first few weeks but is gradual. Most noticeable changes occur after 8–12 weeks on a stable dose. Results are best achieved alongside a reduced-calorie diet and increased physical activity. Individual mounjaro dose titration schedules vary, so timelines differ. Your prescriber will monitor progress and adjust your dose accordingly.
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.