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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Mounjaro 2.5 Mg Pen — NHS & UK Prescribing Information
The Mounjaro 2.5 mg pen is the starting injection dose for adults beginning tirzepatide weight management treatment in the UK. This is the initial dose used during the first four weeks of treatment, whether accessed through NHS specialist services or private prescribing. Understanding what to expect from this dose, how NHS eligibility works, and the tier 3 pathway can help you navigate weight management options available in the UK.
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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.
NHS Eligibility and Access to Mounjaro 2.5 Mg
NHS access to Mounjaro (tirzepatide) is currently available through tier 3 specialist weight management services, though regional availability varies significantly across NHS integrated care boards (ICBs). To be eligible for NHS prescribing of the 2.5 mg starting dose, you typically need a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with at least one weight-related health condition such as type 2 diabetes, hypertension, dyslipidaemia, or sleep apnoea.
For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, lower BMI thresholds may apply — starting at BMI 27.5 or above. The NHS pathway involves a GP referral to your local tier 3 service, which then conducts a clinical assessment before prescribing. Waiting times for NHS specialist services can be substantial in many areas, often ranging from several months to over a year depending on your region.
NICE has approved tirzepatide for use within NHS specialist weight management services, but this does not mean automatic access — ICBs have commissioning discretion. Check your local NHS trust website for current availability and waiting list information.
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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.
Private Access vs NHS Route for the 2.5 Mg Dose
If NHS waiting times are prohibitive, the 2.5 mg Mounjaro pen is also available through private UK prescribing following an online clinical assessment with a UK-licensed prescriber. Private access typically costs £129–£160 per pen (4 weeks supply), depending on the pharmacy. You do not need an NHS referral or specialist tier 3 appointment to access private treatment.
Whichever route you choose — NHS tier 3 or private — the 2.5 mg dose is identical, supplied in the same KwikPen device, and stored at 2–8°C before use. After starting at 2.5 mg for four weeks, the dose increases incrementally (to 5 mg, 7.5 mg, and beyond) based on tolerance and response. Use our GLP-1 weight loss calculator to estimate potential weight loss outcomes at different doses, and our BMI calculator to understand your current health category in NHS terms.
- 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.
Is Mounjaro 2.5 mg available on the NHS?
Yes, NICE has approved tirzepatide for NHS specialist weight management services. However, availability depends on your local NHS ICB's commissioning decisions and tier 3 service capacity. Waiting times vary regionally from several months to over a year. Your GP can refer you to check eligibility and current waiting lists in your area.
What happens after the first 2.5 mg pen?
After four weeks on 2.5 mg, your prescriber will assess your response and side effects. If tolerated well, the dose typically increases to 5 mg for the next four weeks. The dose continues to escalate in steps (5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg) over subsequent weeks, based on individual tolerance and treatment goals.
How much does a Mounjaro 2.5 mg pen cost privately in the UK?
Private Mounjaro 2.5 mg pens typically cost between £129–£160 in the UK, though prices may vary by pharmacy. Each pen contains four weekly doses, so this represents a one-month supply. Always confirm the final cost with the pharmacy before purchasing.
What is tirzepatide and how does it differ from semaglutide (Wegovy)?
Tirzepatide (Mounjaro) is a dual GIP and GLP-1 receptor agonist, whereas semaglutide (Wegovy) activates only the GLP-1pathway. Clinical trials suggest tirzepatide may produce slightly greater average weight loss (~20.9% vs ~14.9%), though individual results vary. Both are once-weekly injections licensed for weight management in the UK.
Do I need a clinical assessment before starting the 2.5 mg pen?
Yes. Whether you access Mounjaro through NHS tier 3 services or private prescribing, a UK-licensed prescriber must assess your medical history, current medications, and suitability. This ensures the treatment is safe and appropriate for you. NHS assessments are conducted by specialist services; private assessments are completed via online consultation.
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