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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Does 2.5mg Mounjaro Work for Weight Loss in the UK?
The 2.5mg dose is the standard starting dose for Mounjaro (tirzepatide) in the UK, but it's not designed to be your final dose. At 2.5mg, weight loss tends to be modest — typically less than the maximum dose — because this is the adjustment phase lasting four weeks. The dose is gradually increased over 16–20 weeks to allow your body to adjust and to reach the therapeutic dose that produces the clinical trial weight loss results. Whether 2.5mg works depends on your individual response and whether you continue the titration schedule. Use our free GLP-1 weight loss calculator to explore projected outcomes at different doses.
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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 Starting Dose for Mounjaro
Mounjaro (tirzepatide) is a prescription-only GIP and GLP-1 receptor agonist approved for weight management in UK adults through NHS specialist tier 3 services. The 2.5mg dose is always the starting point, regardless of your final target dose. This dose titration approach is standard practice because it minimises side effects and allows your body to adapt.
- Week 1–4: 2.5mg once weekly
- Week 5–8: increase to 5mg
- Week 9–12: increase to 7.5mg
- Week 13+: further increases to 10mg, 12.5mg, or 15mg depending on response and tolerance
In the SURMOUNT-1 clinical trial, participants on the full 15mg dose lost approximately 20.9% of their body weight. At the 2.5mg starting dose alone, weight loss is significantly less — typically 3–5% — because this is not a therapeutic dose. NHS NICE guidance recognises tirzepatide as clinically effective when used as part of a comprehensive weight management programme including dietary changes and physical activity. Check your BMI and eligibility using our free BMI calculator.
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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.
NHS vs Private Access and What to Expect
In the UK, Mounjaro is available through two routes: NHS specialist weight management services (tier 3) and private online prescribing. NHS access typically involves referral from your GP to a specialist multidisciplinary team, and availability varies significantly by region. NHS prescribers follow MHRA guidance and NICE recommendations, ensuring comprehensive monitoring. At the 2.5mg starting dose, expect mild to moderate appetite reduction and possible nausea or diarrhoea in the first few weeks — these usually improve as your body adjusts. The key to success is completing the full titration schedule; staying on 2.5mg alone will not produce the weight loss seen in clinical trials. Your prescriber will assess whether this medication is suitable for you based on your individual health profile, BMI, and any weight-related conditions.
- 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 2.5mg Mounjaro enough for weight loss?
No — 2.5mg is the starting dose for four weeks only. It's designed to let your body adjust, not to deliver significant weight loss. The therapeutic effect comes at higher doses (typically 10–15mg). Clinical trials showed 20.9% average weight loss at the maximum 15mg dose, not at 2.5mg. Completing the full dose escalation schedule is essential.
How long do I stay on 2.5mg Mounjaro?
You stay on 2.5mg for four weeks (weeks 1–4). After that, your prescriber will increase your dose to 5mg, provided you've tolerated the 2.5mg dose well. The entire titration to the maximum dose typically takes 16–20 weeks, though some people reach their target dose earlier or take longer depending on side effects.
What are the side effects of 2.5mg Mounjaro in the UK?
Common side effects at 2.5mg include nausea, diarrhoea, constipation, stomach pain, and reduced appetite. These are usually mild at the starting dose and often improve within a week or two as your body adjusts. If side effects are severe, your prescriber may pause the titration or adjust your approach. Serious side effects (severe stomach pain, allergic reactions) require immediate medical attention.
Can I get Mounjaro through the NHS in the UK?
Yes — Mounjaro is approved by NICE and available through NHS specialist weight management services (tier 3). Access requires referral from your GP and assessment by a multidisciplinary team. NHS availability varies by region (integrated care board), and waiting lists can be significant. Private online prescribing is an alternative, requiring a clinical assessment with a UK-licensed prescriber and payment.
Does 2.5mg Mounjaro work better than Wegovy?
Direct comparison at starting doses isn't meaningful — both medications start at subtherapeutic doses. Mounjaro is a dual GIP/GLP-1 agonist; Wegovy is GLP-1 only. Clinical trials showed slightly higher average weight loss with Mounjaro at maximum doses, but individual results vary. Your prescriber will recommend the most suitable option based on your health profile and how your body responds during 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.