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's the Difference Between 2.5 mg and 5 mg Mounjaro?
The key difference between 2.5 mg and 5 mg Mounjaro lies in dose strength and purpose. The 2.5 mg dose is the starting dose used for the first four weeks to help your body adjust to tirzepatide, the active ingredient. The 5 mg dose is the first maintenance dose, typically reached after week five, and is often where many people experience meaningful weight loss support. Both are once-weekly injections delivered via a Mounjaro KwikPen, though the 5 mg dose contains double the tirzepatide concentration. Understanding the difference helps you know what to expect during your dose titration journey.
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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 Mounjaro Dose Titration Works in the UK
Mounjaro uses a dose titration schedule, which means your dose gradually increases over time rather than starting at the maximum. In the UK, the standard schedule works like this: weeks 1–4 require 2.5 mg weekly to allow your body to adjust to tirzepatide and minimise side effects. After four weeks, you progress to 5 mg weekly for weeks 5–8. Each dose increase requires a minimum of four weeks before escalating further. This gradual approach helps manage gastrointestinal side effects like nausea and diarrhoea, which are common when starting GLP-1 and GIP receptor agonist medications. The 5 mg dose is considered the first therapeutic maintenance dose where weight loss support typically becomes more noticeable. Many people remain on 5 mg long-term, though your prescriber may increase to 7.5 mg, 10 mg, 12.5 mg, or the maximum 15 mg dose depending on your response and tolerability. Our GLP-1 weight loss calculator can help you understand potential outcomes at different dose levels.
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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.
Expected Weight Loss at 2.5 mg vs 5 mg Doses
Clinical trial data shows that weight loss support increases with higher Mounjaro doses. At the 2.5 mg starter dose, weight loss is typically modest—many people use this phase primarily for tolerating the medication rather than expecting significant weight reduction. By the 5 mg maintenance dose, clinical evidence suggests more noticeable weight loss support becomes apparent. In the SURMOUNT clinical trials, participants on higher doses (10–15 mg) achieved average weight loss of approximately 19–21% of body weight over 72 weeks, though individual results vary considerably. At 5 mg, results fall between the starter dose and maximum doses, typically supporting weight loss of around 8–15% alongside a reduced-calorie diet and increased physical activity. Important to note: these are averages from clinical trials. Your personal outcome depends on genetics, adherence, diet, exercise, and individual response to tirzepatide. Track your progress with our free progress tracker to monitor changes over time.
- 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 do I start on 2.5 mg Mounjaro if the effective dose is 5 mg?
The 2.5 mg starter dose allows your body to adapt to tirzepatide gradually, reducing nausea, diarrhoea, and other gastrointestinal side effects. This approach improves tolerability and helps you progress safely through the dose titration schedule. After four weeks, you advance to 5 mg, which is when more substantial weight loss support typically begins.
Can I skip the 2.5 mg dose and start directly on 5 mg Mounjaro?
No. UK prescribers follow the standard dose titration schedule, which requires starting at 2.5 mg for weeks 1–4. Starting directly at 5 mg significantly increases the risk of severe side effects and is not part of the licensed dosing protocol. Your prescriber will follow the established schedule for safety.
How much weight will I lose on 5 mg Mounjaro?
Individual results vary significantly. Clinical trials show average weight loss ranges from 8–15% of body weight at 5 mg doses, though some people lose more and some less. Weight loss depends on your genetics, diet adherence, physical activity, and individual response to tirzepatide. Your GP can discuss realistic expectations for your situation.
When should I expect to move from 2.5 mg to 5 mg?
You progress from 2.5 mg to 5 mg after four weeks of the starter dose—typically at week five of treatment. Your prescriber will confirm this transition is appropriate based on how you've tolerated the initial dose. If you're experiencing severe side effects, progression may be delayed.
Is 5 mg Mounjaro the maximum recommended dose?
No. 5 mg is the first maintenance dose, not the maximum. Mounjaro doses continue up to 15 mg weekly, the licensed maximum. Your prescriber may increase to 7.5 mg, 10 mg, 12.5 mg, or 15 mg depending on your weight loss response and tolerability. Dose increases occur every four weeks.
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.