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?
The 2.5mg dose of Mounjaro (tirzepatide) is the standard starting dose in the UK, designed to help your body adjust to the medication rather than deliver maximum weight loss results. In clinical trials, participants typically stayed on 2.5mg for only 4 weeks before moving to higher doses. Whether it works for you depends on your individual circumstances, how your body responds, and whether you progress to maintenance doses. The NHS prescribes Mounjaro through specialist tier 3 weight management services, and your GP can refer you if you meet eligibility criteria. Results vary significantly between individuals, so it's important to understand what to expect at this starting dose and how dose titration works over time.
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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.
How Mounjaro Starting Dose Works in UK Practice
The 2.5mg starting dose of Mounjaro is not designed for long-term weight loss — it's an adjustment phase that allows your body to adapt to tirzepatide and helps your GP monitor tolerance and side effects. In the SURMOUNT-1 clinical trial (the UK and Europe basis for approval), participants spent only 4 weeks at 2.5mg before escalating. At this dose, weight loss is typically modest: clinical data shows participants lost an average of 2–3kg in the first month, though some experienced no significant loss at all.
The therapeutic benefit increases as you progress through doses: 5mg, 7.5mg, 10mg, 12.5mg, and finally 15mg (the maximum). Average weight loss across the trial ranged from approximately 15% body weight at 5mg to 20.9% at 15mg over 72 weeks. Your GP will assess whether you need dose escalation based on your response and tolerance. For NHS prescribing through NICE guidance, you must meet eligibility criteria: BMI 30 or above, or BMI 27–29.9 with a weight-related health condition such as type 2 diabetes or hypertension. Use our free BMI calculator to check your starting position and understand what dose escalation might mean for your individual situation.
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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.
Getting Mounjaro on the NHS vs Private Route
Access to Mounjaro in the UK differs significantly between NHS and private routes. On the NHS, you're referred to a tier 3 specialist weight management service, where a multidisciplinary team (including a doctor, dietitian, and psychologist) assesses your eligibility and monitors your progress. Waiting lists can be substantial — some regions have waits of 12 months or longer. Via private prescribing, you can access Mounjaro faster through an online clinical assessment with a UK-licensed prescriber, with prescriptions dispensed by a GPhC-registered pharmacy. The private route costs approximately £129–£180 per month depending on dose.
Regardless of route, you'll receive your medication in a KwikPen — a pre-filled injection device containing 4 doses (a 4-week supply). Whether NHS or private, you must demonstrate that you're making lifestyle changes: reduced-calorie diet and increased physical activity. Weight loss without behaviour change is unlikely to succeed at any dose.
- 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.
Will 2.5mg Mounjaro help me lose weight?
The 2.5mg starting dose is primarily for dose tolerance and adjustment. Most people lose 2–3kg in the first month, but significant weight loss typically occurs at higher doses (5mg and above). Individual results vary widely — some people see modest loss, others see none at the starting dose. Your GP will assess whether escalation is appropriate.
How long do you stay on 2.5mg Mounjaro in the UK?
In UK practice and clinical trials, 2.5mg is typically maintained for 4 weeks only. If you tolerate it well and lose weight, your GP will escalate to 5mg. If you experience significant side effects, your GP may keep you at 2.5mg slightly longer or adjust the escalation plan based on your individual response.
Does Mounjaro kwikpen come pre-filled at 2.5mg?
Yes, each KwikPen comes pre-filled with either 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, or 15mg — depending on your dose. Each pen contains 4 weeks' worth of doses (one injection per week). Your prescription specifies which dose strength you receive.
Is Mounjaro available on the NHS for weight loss in the UK?
Yes — NICE has approved tirzepatide (Mounjaro) for weight management on the NHS for eligible adults. Access is through specialist tier 3 weight management services, typically via GP referral. Eligibility requires BMI 30+ or BMI 27–29.9 with weight-related health conditions. Availability and waiting times vary significantly by region.
How does Mounjaro vs Wegovy compare when starting out?
Both are once-weekly injections, but Mounjaro is a dual GIP+GLP-1 agonist while Wegovy is GLP-1 only. Mounjaro's starting dose (2.5mg) may provide slightly more appetite suppression than Wegovy's starting dose (0.25mg). Clinical trials show Mounjaro achieved marginally higher average weight loss, but individual response varies. Your GP will recommend which is appropriate for you.
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.