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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How Does 2.5 Mg Mounjaro Compare to Wegovy?
The 2.5 mg Mounjaro dose is the starting dose for weight management in the UK, but it's not directly comparable to Wegovy by weight alone. Mounjaro and Wegovy are different medications with different mechanisms: Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. This means 2.5 mg of Mounjaro is not equivalent to a specific Wegovy dose. Your prescriber will assess which medication suits your health profile. Use our GLP-1 weight loss calculator to explore potential outcomes at different doses.
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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.
Mounjaro 2.5 Mg vs Wegovy: Mechanism and Dosing Differences
Mounjaro (tirzepatide) at 2.5 mg is the initial starter dose in the UK Mounjaro UK prescription pathway. It activates two hormone pathways simultaneously — GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 — which is why it's classified as a dual agonist. This dual mechanism distinguishes it from Wegovy.
Wegovy (semaglutide) starts at a much lower dose: 0.25 mg in week one, escalating to 0.5 mg, 1 mg, 1.7 mg, and finally 2.4 mg (the maintenance dose). Wegovy activates only the GLP-1 pathway.
Because the mechanisms differ, 2.5 mg Mounjaro is not directly comparable to any single Wegovy dose. Clinical trial data (SURMOUNT for Mounjaro, STEP for Wegovy) shows both medications support weight loss, but through slightly different biological pathways. The approximate equivalence used by some prescribers suggests 2.5 mg Mounjaro is roughly comparable to Wegovy's 0.25–0.5 mg range, but this is not an official conversion and requires individual assessment.
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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.
Which Medication Is Right for You? Clinical Assessment First
Neither Mounjaro nor Wegovy can be recommended for you without a clinical assessment from a UK-licensed prescriber. Both require a prescription and both are prescribed based on your individual health profile, BMI, weight-related conditions, and any contraindications.
Your prescriber will consider:
- Your BMI and eligibility under UK guidelines
- Any weight-related health conditions (diabetes, high blood pressure, heart disease risk)
- Your medical history and current medications
- Your preferences regarding injection frequency (both are once-weekly, but administration experience may vary)
- Previous weight loss medication use
Both medications are available through NHS specialist weight management services and private prescription routes in the UK. Access to Mounjaro and Wegovy varies by region on the NHS, so your GP can advise on local options. Calculate your BMI using our free BMI calculator above to understand your starting point.
- 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.
Is 2.5 mg Mounjaro the same strength as any Wegovy dose?
No. 2.5 mg Mounjaro is the starting Mounjaro dose in the UK, whilst Wegovy starts at 0.25 mg. They use different mechanisms (dual GIP+GLP-1 vs GLP-1 only), so direct mg-to-mg comparison is not meaningful. Approximate clinical equivalence suggests 2.5 mg Mounjaro may be comparable to 0.5–1 mg Wegovy, but this varies individually and must be assessed by a prescriber.
Can I switch from Mounjaro 2.5 mg to Wegovy?
Yes, switching between medications is possible under prescriber guidance. However, there is no official NHS conversion chart. Your prescriber will reassess you before switching and may restart you on Wegovy's starting dose (0.25 mg) or escalate based on clinical judgement. Always inform your prescriber before making any change.
Why is Mounjaro's starting dose (2.5 mg) higher than Wegovy's (0.25 mg)?
The dose ranges reflect the different potencies and mechanisms of the drugs. Mounjaro's dual GIP+GLP-1 action means a lower absolute dose achieves biological effects comparable to higher Wegovy doses. Neither is "stronger" in absolute terms — they work differently, so dosing strategies differ.
What does the SURMOUNT trial show about Mounjaro 2.5 mg?
The SURMOUNT-1 trial showed that participants on Mounjaro 5 mg (not 2.5 mg) achieved an average weight loss of approximately 15% body weight over 72 weeks. The 2.5 mg dose is a starting/titration dose, not typically the dose used in long-term studies. Results vary individually.
How do I know if Mounjaro or Wegovy is prescribed on the NHS in my area?
NHS access to Mounjaro and Wegovy is managed through tier 3 specialist weight management services and varies by region (ICB). Ask your GP about referral to your local specialist service. They can advise on availability and waiting times. Private prescription options are also available through UK-licensed online prescribers.
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