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
What Is 2.5mg Mounjaro and How Does It Work?
The 2.5mg dose of Mounjaro (tirzepatide) is the standard starting dose for weight management in UK adults. This is the first step in a dose escalation plan, designed to help your body adjust to the medication while minimising side effects. Mounjaro is a prescription-only GLP-1 and GIP receptor agonist — meaning it works through two natural hormone pathways to help regulate appetite and support weight management. The 2.5mg dose is taken as a once-weekly injection using a pre-filled KwikPen. Your prescriber will assess your individual needs and suitability before recommending Mounjaro, and you'll need to use the BMI calculator or speak with your GP about your eligibility.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
2.5mg Mounjaro: Starting Dose and NHS Prescribing in the UK
2.5mg is the mandatory starting dose for all adults beginning Mounjaro treatment in the UK. This dose is taken once weekly for the first four weeks, after which your prescriber may increase to the next dose level (5mg) if appropriate.
Why start with 2.5mg? This lower starting dose allows your body to adjust to the medication, reducing the likelihood of severe side effects like nausea, vomiting, and stomach upset. The dose titration schedule is designed to balance efficacy with tolerability.
NHS eligibility for Mounjaro: The medication is available through NHS tier 3 specialist weight management services for adults with a BMI of 30 or above, or BMI 27–29.9 with weight-related health conditions (type 2 diabetes, prediabetes, hypertension, dyslipidaemia, sleep apnoea, or cardiovascular disease). South Asian, Chinese, Black African, and Black Caribbean adults may qualify at lower BMI thresholds due to higher health risks.
Access routes: NHS access is through specialist weight management services (significant regional variation and waiting lists). Private prescribing is available through GPhC-registered online services following a clinical assessment, with no NHS referral required.
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.
NHS vs Private Access to 2.5mg Mounjaro in the UK
NHS prescribing: NICE has approved tirzepatide (Mounjaro) for use within NHS specialist tier 3 services for eligible adults. Access is through your GP referral to a specialist weight management service in your local ICB. Waiting lists vary significantly by region — some areas have lists of several months. Your prescriber will assess your medical history, weight, health conditions, and medications before confirming eligibility.
Private prescribing: If NHS waiting lists are too long, 2.5mg Mounjaro is available privately through regulated UK prescribing services. A licensed prescriber will conduct an online clinical assessment (including questions about your health, medications, and weight). If approved, a prescription is issued to a GPhC-registered pharmacy. Cost typically ranges from £129–£180 per month for starting doses, depending on provider.
Both routes require a proper clinical assessment — Mounjaro is prescription-only and not suitable for everyone. Use our free GLP-1 weight loss calculator to understand potential outcomes, and speak with your GP about which route suits you best.
- 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 the same as the maximum dose?
No. 2.5mg is the starting dose only. The maximum dose is 15mg per week. Your prescriber will increase your dose every four weeks if tolerated, stepping up to 5mg, 7.5mg, 10mg, 12.5mg, and finally 15mg. Most people reach maintenance at a lower dose based on their individual response.
Can I start on a higher dose of Mounjaro to lose weight faster?
No. UK prescribing guidelines require all patients to start at 2.5mg regardless of weight or urgency. Starting lower reduces side effects and allows your body to adapt. Faster weight loss is not recommended without medical supervision and may increase muscle loss risk.
How long do I stay on 2.5mg Mounjaro?
You remain on the 2.5mg dose for four weeks (one injection per week for four weeks). After the fourth injection, if you're tolerating it well, your prescriber will move you to 5mg. If side effects are problematic, the timeline may be extended.
What are the side effects of 2.5mg Mounjaro?
Common side effects at the starting dose include nausea, diarrhoea, constipation, and stomach pain. These typically improve as your body adjusts. Serious side effects are rare but include severe stomach pain (possible pancreatitis) and serious allergic reactions. Always report persistent or severe symptoms to your prescriber.
Can I get 2.5mg Mounjaro on the NHS straight away?
Not immediately. You'll need a GP referral to your local NHS tier 3 weight management service first. They'll assess your eligibility, health history, and suitability. Once approved, you'll receive 2.5mg as the starting dose. NHS waiting times vary by region from weeks to many months depending on service capacity.
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.