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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Mounjaro 2.5mg vs 5mg: UK Dose Differences Explained
Mounjaro (tirzepatide) comes in different doses, with 2.5mg and 5mg serving different purposes in your treatment plan. The 2.5mg dose is your starting point, designed to help your body adjust to the medication, while 5mg is typically your first maintenance dose after four weeks. Understanding the difference between these two doses — and why your prescriber uses dose titration — is essential for managing expectations and side effects during your weight management journey in the UK.
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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.
Starting Dose vs First Maintenance Dose
Mounjaro 2.5mg is your initial starting dose, taken as a once-weekly injection for your first four weeks. This is standard across all UK prescribing. The 2.5mg dose allows your body to adapt to how tirzepatide works, which helps minimise nausea and other gastrointestinal side effects that are common when starting GLP-1 or dual receptor agonist medications. You remain on 2.5mg for exactly four weeks before any dose increase.
Mounjaro 5mg is your first step up, typically started in week five. Most people tolerate this dose well after the initial adjustment period. Clinical data shows that 5mg produces modest weight loss — averaging around 15% of body weight in trials — though individual results vary significantly. Your prescriber may keep you on 5mg as your maintenance dose if it's working well, or continue increasing every four weeks up to the maximum 15mg dose.
- 2.5mg = weeks 1–4 (starting/titration phase)
- 5mg = weeks 5+ (first maintenance option)
- Each dose step = minimum 4 weeks apart
- Maximum dose = 15mg once weekly
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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
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Why Dose Titration Matters in UK Prescribing
Dose titration — gradually increasing your Mounjaro dose every four weeks — is standard practice because it improves tolerability and safety. Starting at 2.5mg rather than jumping to 5mg reduces the risk of severe nausea, vomiting, and appetite loss that might otherwise make the medication difficult to continue. This is especially important because your prescriber needs you to stay on the medication long-term for sustained weight loss results.
The NHS and private prescribers both follow the same titration schedule. If you're accessing Mounjaro through an NHS tier 3 specialist weight management service or a private online prescription following clinical assessment, your dosing plan will follow this same four-week step progression. Your GP or prescriber will discuss whether staying at 5mg or continuing to escalate is right for your individual health and weight loss goals.
- 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.
Can I start Mounjaro at 5mg instead of 2.5mg?
No. All UK prescribers, whether NHS or private, start patients at 2.5mg for the first four weeks. This is a safety standard because starting at a higher dose significantly increases nausea and gastrointestinal side effects. The initial titration phase helps your body adapt before moving to 5mg or beyond.
How much weight loss can I expect on 2.5mg Mounjaro?
Weight loss on 2.5mg is typically modest because it's a short-term starting dose (four weeks only). Most patients see minimal weight loss at this dose. The significant weight loss usually begins once you reach 5mg and beyond, where clinical trials showed around clinically studied weight loss on average — though individual results vary.
Should I stay on 5mg or keep increasing my Mounjaro dose?
That depends on your individual results, side effects, and health goals. Your prescriber will assess whether 5mg is producing good weight loss and tolerability. If you're losing weight steadily and side effects are manageable, you may stay at 5mg. If progress stalls or you tolerate it well, your dose may increase every four weeks up to 15mg maximum.
Is the dose titration the same on NHS and private Mounjaro prescriptions?
Yes. Both NHS specialist services and private prescribers follow the same MHRA-approved dosing schedule: 2.5mg weeks 1–4, then 5mg weeks 5–8, with optional escalation every four weeks. The only difference is access route and cost, not the actual treatment protocol.
What side effects should I expect moving from 2.5mg to 5mg?
When stepping up to 5mg in week five, some patients experience increased nausea, diarrhoea, or appetite changes for a few days as their body adjusts to the higher dose. These typically settle within a week. If side effects are severe, contact your prescriber — they may recommend staying at 5mg longer before further increases.
Ready to take control of your weight loss journey?
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