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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Understanding 2.5mg vs 5mg Mounjaro Doses
The 2.5mg and 5mg doses of Mounjaro (tirzepatide) serve different purposes in your weight management treatment. The 2.5mg dose is your starting point — designed to help your body adjust to the medication and reduce nausea. The 5mg dose is typically the first maintenance dose, where most people begin to see more significant effects on appetite and weight. Understanding the difference between these doses helps you know what to expect as your treatment progresses and why your GP or prescriber structures your dose titration schedule the way they do.
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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 structured dose titration schedule, meaning you start low and increase gradually every four weeks. The 2.5mg dose is your initial adjustment dose, typically used during weeks 1–4 of treatment. This allows your body to adapt to the medication and helps minimise side effects like nausea and stomach upset.
- 2.5mg weeks 1–4: Starting dose, body adjustment phase
- 5mg weeks 5–8: First maintenance dose, increased appetite suppression
- 7.5mg onwards: Further escalation if needed, based on response and tolerability
You must stay on each dose for a full four weeks before increasing. Skipping this step raises the risk of severe side effects. The 5mg dose represents a doubling of the starting dose, which is why the difference in effect can be noticeable — you're receiving twice as much active tirzepatide. Clinical data shows that weight loss begins to accelerate at the 5mg dose compared to 2.5mg, though individual responses vary significantly.
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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.
Practical Differences: What You'll Experience
At 2.5mg, many people experience mild appetite suppression and adjustment side effects — nausea is common in the first week or two. By the time you reach 5mg, your body has usually adapted, side effects often settle, and appetite suppression becomes more pronounced. You may notice you eat smaller portions more naturally and feel full sooner.
The transition from 2.5mg to 5mg typically feels manageable if you've tolerated the starting dose well. Some people find the appetite suppression noticeably stronger at 5mg. Use our free GLP-1 weight loss calculator to estimate potential weight loss outcomes at different doses, though remember that individual results vary based on diet, activity, and personal metabolism. Track your progress using our progress tracker to monitor how each dose affects you personally.
- 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 you start on 2.5mg Mounjaro instead of jumping straight to 5mg?
Starting at 2.5mg allows your body to adapt to the medication and reduces the risk of severe side effects, particularly nausea. This lower starting dose is a standard prescribing practice across all weight loss GLP-1 medications. After four weeks, if you've tolerated 2.5mg well, increasing to 5mg becomes safe and effective.
When should I move from 2.5mg to 5mg Mounjaro?
Your prescriber will recommend moving to 5mg after you've completed four weeks at 2.5mg. This is based on tolerability rather than response — as long as you haven't experienced severe side effects, progression to 5mg proceeds on schedule. Your GP will monitor your progress during this transition.
Is the difference between 2.5mg and 5mg Mounjaro significant for weight loss?
Yes — clinical trial data shows measurable differences in weight loss between doses. However, individual results vary considerably. The 5mg dose typically produces more noticeable appetite suppression and supports greater weight loss than 2.5mg when combined with diet and exercise changes.
Can I stay on 2.5mg Mounjaro if it's working well for me?
Possibly, but most prescribers follow the standard titration schedule and progress to 5mg after four weeks. Some people do plateau on lower doses and achieve their weight loss goals. Discuss this with your prescriber — any decision to stay on a dose requires clinical assessment based on your individual response.
What happens to side effects when you increase from 2.5mg to 5mg?
For many people, side effects like nausea actually improve or stabilise at 5mg because your body has adapted. However, some people experience a brief return of mild nausea during the transition week. This typically resolves within days as your body adjusts to the higher dose.
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.