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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2.5 Ml Mounjaro — NHS Prescribing Guide for UK Adults
The 2.5 ml starting dose of Mounjaro (tirzepatide) is the first step in UK weight management treatment. This initial dose helps your body adjust to the GLP-1 and GIP receptor agonist medication over the first 4 weeks, before escalation to higher doses like 5 mg. Understanding NHS eligibility, NICE guidance, and the full dose titration pathway can help you determine whether this prescription-only injection is right for you. Use our free BMI calculator above to check your current weight status and see where you sit against NHS criteria for specialist weight management services.
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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.
NHS Eligibility and NICE Guidance for Mounjaro Starting Dose
NICE approved tirzepatide (Mounjaro) for use within NHS specialist weight management services in England, marking a significant update to UK prescribing guidelines. The 2.5 ml starting dose is prescribed only through NHS tier 3 or tier 4 specialist weight management services—not by standard GPs. You are eligible for consideration if you have a BMI of 30 kg/m² or above, or BMI of 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Adults of South Asian, Chinese, Black African, or Black Caribbean heritage may qualify at lower BMI thresholds (from BMI 27.5). The 2.5 ml dose is maintained for 4 weeks to allow your body to adjust. During this time, your prescriber monitors tolerability before moving to the 5 mg dose. NHS access is free but involves waiting lists that vary significantly by region—some areas have delays of many months. Private online prescribing offers faster access but requires payment, typically from £129 per month depending on dose and provider.
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.
Dose Titration and Transitioning Beyond 2.5 Ml
After 4 weeks on the 2.5 ml starting dose, your prescriber will review your progress and side effects before escalating to 5 mg. This measured titration approach reduces gastrointestinal side effects and allows your body to adapt to how the medication affects appetite, gastric emptying, and blood sugar regulation. The full Mounjaro dose escalation pathway goes: 2.5 mg weeks 1–4 → 5 mg weeks 5–8+ → 7.5 mg weeks 9–12+ → 10 mg weeks 13–16+ → 12.5 mg weeks 17–20+ → 15 mg (maximum). Clinical trials showed that average weight loss increases with higher doses—2.5 mg alone produces modest results, while 15 mg achieved approximately clinically studied weight loss. However, individual outcomes vary significantly. Use our GLP-1 weight loss calculator to estimate potential weight loss across different doses.
- 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 2.5 ml Mounjaro available on the NHS in the UK?
Yes, NICE has approved tirzepatide for NHS use within specialist tier 3/4 weight management services. However, availability is limited and varies by region. You must be referred by your GP to a specialist service, and waiting lists can be lengthy. Private prescribing offers faster access.
What happens after 4 weeks on the 2.5 ml starting dose?
After 4 weeks, your prescriber reviews your tolerability and weight loss. If side effects are manageable, you will typically escalate to the 5 mg dose. If side effects are severe, you may remain on 2.5 ml longer or discontinue. Each dose increase happens minimum 4 weeks apart.
How much weight can I expect to lose on 2.5 ml Mounjaro alone?
The 2.5 ml starting dose produces modest weight loss—clinical trials showed average losses around 5–8% of body weight at this dose. Larger weight loss typically occurs at higher doses (5 mg and above). Individual results vary based on diet, activity, and metabolism. Calculate your own projection using our free GLP-1 weight loss calculator.
What are the main side effects of Mounjaro at the 2.5 ml starting dose?
Very common side effects include nausea, diarrhoea, vomiting, and stomach pain. These often ease over the first 2–4 weeks as your body adjusts. Less common are injection site reactions, fatigue, and headache. Serious side effects (severe stomach pain, pancreatitis signs) require urgent medical attention.
How do I access Mounjaro 2.5 ml through the NHS?
Ask your GP for a referral to your local NHS tier 3 specialist weight management service. Eligibility requires BMI ≥30 (or ≥27 with comorbidities). After assessment, you'll be prescribed and given support throughout your dose escalation journey. Waiting times vary by region and ICB funding.
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.