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
Mounjaro 2.5mg: Your NHS Starting Dose Explained
Mounjaro 2.5mg is the initial starting dose when you begin tirzepatide treatment for weight management in the UK. This lower dose allows your body to adjust to the medication whilst you're assessed for suitability and tolerability. If you're considering Mounjaro through the NHS or privately, understanding the 2.5mg phase is essential to setting realistic expectations for your weight loss journey.
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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 How the 2.5mg Dose Works
To access Mounjaro 2.5mg through the NHS, you must be referred to a tier 3 specialist weight management service by your GP. Eligibility requires 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, high blood pressure, or sleep apnoea. For adults of South Asian, Chinese, Black African, or Black Caribbean heritage, eligibility starts at a BMI of 27.5 kg/m² due to higher health risks at lower thresholds.
The 2.5mg dose is taken once weekly by injection using the Mounjaro KwikPen. You'll remain on this starting dose for a minimum of 4 weeks to allow your body to tolerate the medication and for your prescriber to assess how you're responding. This dual GIP and GLP-1 receptor agonist works by helping regulate appetite and supporting you to feel fuller after smaller meals. NHS availability varies significantly by region and waiting lists can be lengthy in many areas.
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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.
Moving Beyond 2.5mg and NHS vs Private Access
After 4 weeks on the 2.5mg dose, your prescriber may increase you to 5mg if tolerated well. The dose escalates by 2.5mg increments every 4 weeks, potentially reaching 15mg as the maximum dose. Most weight loss occurs at higher doses, so the 2.5mg phase is primarily about safety and tolerance rather than significant weight reduction.
You can access Mounjaro 2.5mg through the NHS specialist services or privately via a UK-licensed prescriber following an online clinical assessment. Private access avoids NHS waiting lists and provides more rapid treatment initiation. Calculate your potential progress using our GLP-1 weight loss calculator, and track your results with our free progress tracker as you progress through the dose escalation phases.
After 4 weeks on the 2.5mg dose, your prescriber may increase you to 5mg if tolerated well. The dose escalates by 2.5mg increments every 4 weeks, potentially reaching 15mg as the maximum dose. Most weight loss occurs at higher doses, so the 2.5mg phase is primarily about safety and tolerance rather than significant weight reduction.
You can access Mounjaro 2.5mg through the NHS specialist services or privately via a UK-licensed prescriber following an online clinical assessment. Private access avoids NHS waiting lists and provides more rapid treatment initiation. Calculate your potential progress using our GLP-1 weight loss calculator, and track your results with our free progress tracker as you progress through the dose escalation phases.
- 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 2.5mg available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is available through NHS tier 3 specialist weight management services for eligible adults. You'll need a GP referral and must meet BMI or health condition criteria. Availability and waiting times vary significantly by region. NICE has approved tirzepatide for use within NHS weight management services.
How long do I stay on the 2.5mg starting dose?
You remain on Mounjaro 2.5mg for a minimum of 4 weeks. This allows your body to adjust and your prescriber to assess tolerability. After 4 weeks, if tolerated well, the dose typically increases to 5mg, then by 2.5mg increments every 4 weeks up to a maximum of 15mg weekly.
What side effects should I expect on Mounjaro 2.5mg?
Common side effects at the starting dose include nausea, diarrhoea, constipation, and stomach pain. These often reduce over the first few weeks as your body adjusts. Most side effects are mild at the lowest dose. Report any severe or persistent symptoms to your prescriber immediately.
Will I lose significant weight on the 2.5mg dose?
The 2.5mg starting dose is primarily about tolerability and safety, not maximum weight loss. Clinical trials show most weight loss occurs at higher doses (10–15mg). Use our BMI calculator to establish your baseline, and expect gradual progress as your dose increases over the coming weeks and months.
What's the difference between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) activates only the GLP-1pathway. Both are once-weekly injections available through NHS services and privately. Clinical trials suggest Mounjaro may produce slightly greater average weight loss, though individual results vary considerably.
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.