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 2.5 mg Starting Dose — How Much in ml?
Mounjaro's starting dose of 2.5 mg is the initial step in the medication's dose titration schedule. In terms of volume, a 2.5 mg dose of Mounjaro delivered via the KwikPen contains 0.6 ml of solution. This is lower than Wegovy's starting dose, which reflects their different mechanisms and clinical trial designs. Both medications are prescription-only and require a clinical assessment before being prescribed in the UK. Understanding how these starting doses work is important if you're considering either option for weight management.
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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.
How Mounjaro and Wegovy Starting Doses Compare
Mounjaro (tirzepatide) starts at 2.5 mg once weekly, delivered as 0.6 ml via the KwikPen auto-injector. This is a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways to help regulate appetite and support weight management. The SURMOUNT clinical trials showed that even at this starting dose, participants began experiencing appetite suppression and early weight loss signals.
Wegovy (semaglutide) starts at 0.25 mg once weekly, which is a smaller volume than Mounjaro's starting injection. It is a GLP-1 receptor agonist only—activating a single hormone pathway. The STEP clinical trials demonstrated weight loss progression from this lower starting point, with dose escalation occurring over several weeks. Both medications are prescription-only in the UK and require a clinical assessment by a licensed prescriber before starting. Your individual health status, medical history, and weight management goals will determine which option, if either, may be suitable for you.
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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.
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Mounjaro vs Wegovy: Trial Data and Prescriber Decision
Clinical evidence from SURMOUNT-1 (Mounjaro) and STEP-1 (Wegovy) shows both medications support weight loss when combined with a reduced-calorie diet and increased physical activity. Mounjaro's dual mechanism may offer a different efficacy profile, whilst Wegovy's established single GLP-1 pathway has extensive long-term safety data. Neither medication assures specific weight loss—individual results vary significantly. A UK licensed prescriber will assess your eligibility based on BMI thresholds, weight-related health conditions, and personal circumstances. Both are available through NHS specialist weight management services (tier 3) or private online prescribing following clinical assessment. Use our free GLP-1 weight loss calculator to explore potential outcomes at different doses.
- 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.
What does 2.5 mg of Mounjaro equal in ml?
Mounjaro 2.5 mg contains 0.6 ml of solution delivered via the KwikPen. This is the standard starting dose in the Mounjaro titration schedule. Each pre-filled pen contains enough for one weekly injection.
Why does Mounjaro start at a higher dose than Wegovy?
Mounjaro (2.5 mg) and Wegovy (0.25 mg) have different starting doses because they are different medications with different mechanisms. Mounjaro is a dual GIP and GLP-1 agonist; Wegovy is GLP-1 only. Their dose titration schedules reflect their individual clinical trial designs (SURMOUNT and STEP respectively).
Which starting dose is more effective for weight loss?
Both Mounjaro and Wegovy's starting doses initiate weight loss when combined with lifestyle changes. Individual response varies. Clinical trials show average weight loss of approximately 15% with Mounjaro and 14.9% with Wegovy—but results depend on your personal factors and adherence.
Can I switch between Mounjaro and Wegovy?
Switching between medications must be managed by your prescriber. There is no official conversion chart between Mounjaro and Wegovy—approximate equivalences exist based on clinical practice, but any switch requires medical supervision and assessment.
How do I know which medication is right for me?
A UK licensed prescriber will assess your individual eligibility, medical history, BMI, weight-related health conditions, and personal preferences. Both require prescription-only status and clinical assessment. Neither is right for everyone. Your GP or specialist will advise which is appropriate for you.
Ready to take control of your weight loss journey?
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