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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What Is 2.5mg of Mounjaro and How Does It Work?
2.5mg is the starting dose of Mounjaro (tirzepatide) — the lowest strength available in the UK. It's a prescription-only, once-weekly injection designed to help regulate appetite and support weight management. This initial dose is used during your first four weeks of treatment, allowing your body to adjust before your prescriber may increase you to 5mg. Understanding what this dose does and how it fits into the NHS and UK prescribing pathway can help you make informed decisions about weight management options available to you.
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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.
How 2.5mg of Mounjaro Works as a Starting Dose
2.5mg is a low-dose starting point for tirzepatide therapy. At this dose, Mounjaro acts as a dual GIP and GLP-1 receptor agonist — activating two natural hormone pathways that help regulate appetite, reduce food cravings, and support feeling fuller after smaller meals. You remain on 2.5mg for weeks 1–4, giving your body time to adjust and helping minimise early side effects like nausea or stomach discomfort.
Unlike higher doses (5mg, 10mg, 15mg), the 2.5mg starting dose is typically gentler, though individual responses vary. Your prescriber will assess your tolerance and health response during this period. If you tolerate it well, the dose is usually increased to 5mg at week 5 — a process called dose titration. Each KwikPen contains four injections (four weeks of treatment), so you'll need a new pen when stepping up to the next dose.
You can use our free GLP-1 weight loss calculator to explore projected outcomes at different doses, though the 2.5mg starting phase is typically brief and results at this dose alone are modest compared to maintenance doses.
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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.
2.5mg Mounjaro and NHS UK Eligibility
Access to Mounjaro (tirzepatide) through the NHS in the UK is managed through tier 3 specialist weight management services. Prescribing follows NICE guidance for eligible adults: BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds (27.5+) apply to those of South Asian, Chinese, Black African, or Black Caribbean heritage, reflecting higher metabolic risk in these groups.
Once prescribed through NHS specialist services, your GP or specialist will initiate you on 2.5mg and manage dose increases over time. NHS access typically involves waiting lists and regional variation — availability differs significantly across England, Scotland, Wales, and Northern Ireland. Private prescribing routes also exist: licensed UK prescribers can assess and prescribe Mounjaro following an online consultation with a GPhC-registered pharmacy, without NHS referral.
Access to Mounjaro (tirzepatide) through the NHS in the UK is managed through tier 3 specialist weight management services. Prescribing follows NICE guidance for eligible adults: BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Lower BMI thresholds (27.5+) apply to those of South Asian, Chinese, Black African, or Black Caribbean heritage, reflecting higher metabolic risk in these groups.
Once prescribed through NHS specialist services, your GP or specialist will initiate you on 2.5mg and manage dose increases over time. NHS access typically involves waiting lists and regional variation — availability differs significantly across England, Scotland, Wales, and Northern Ireland. Private prescribing routes also exist: licensed UK prescribers can assess and prescribe Mounjaro following an online consultation with a GPhC-registered pharmacy, without NHS referral.
- 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.
Why start at 2.5mg instead of a higher dose of Mounjaro?
The 2.5mg starting dose reduces the risk of side effects and allows your body to adjust to tirzepatide. Common early side effects like nausea are less intense at lower doses. After four weeks at 2.5mg, your prescriber assesses your tolerance and may increase you to 5mg. This gradual approach improves tolerability and medication persistence.
How long do you stay on 2.5mg of Mounjaro?
You typically remain on 2.5mg for four weeks (weeks 1–4 of treatment). At week 5, if tolerated well, your dose increases to 5mg. This four-week minimum on each dose — called dose titration — is the standard NHS and clinical trial protocol. Individual adjustments may vary based on your response and your prescriber's assessment.
Is 2.5mg enough for weight loss?
2.5mg alone produces minimal weight loss compared to higher maintenance doses (5mg–15mg). Weight loss results are modest during the initial four weeks. The 2.5mg phase is primarily for tolerance-building. Meaningful weight loss typically occurs once you reach maintenance doses (5mg+). Individual results vary significantly, and results depend on lifestyle changes alongside medication.
Can you get 2.5mg Mounjaro on the NHS?
Yes, 2.5mg Mounjaro is available through NHS specialist tier 3 weight management services if you meet NICE eligibility criteria (BMI ≥30, or ≥27 with weight-related health conditions). Your GP can refer you to your local service, though waiting lists vary by region. Private prescribing is also available through licensed UK prescribers and GPhC-registered pharmacies without NHS referral.
What's the difference between 2.5mg Mounjaro and 2.5mg Wegovy?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications. Mounjaro is a dual GIP+GLP-1 agonist; Wegovy is a GLP-1-only agonist. Both start at low doses to minimise side effects, but Wegovy starts at 0.25mg (much lower). 2.5mg Mounjaro is higher than typical starting Wegovy doses. Both require prescription and clinical assessment in the UK.
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