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 Every 6 Days vs Wegovy — How Do They Compare?
Mounjaro is designed as a once-weekly injection, not every 6 days, but comparing Mounjaro and Wegovy is essential for UK adults considering weight management medications. Both are prescription-only GLP-1 based treatments, but they work differently and follow different dosing schedules. This guide explains the clinical trial data, mechanism differences, and how prescribers decide which medication might suit you. Your GP or prescriber will assess your individual health needs before recommending either option.
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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 and Wegovy Work Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two separate hormone pathways to regulate appetite and blood sugar. Wegovy (semaglutide) is a GLP-1 agonist only, activating a single pathway. This difference in mechanism means they may produce different effects in individuals. Clinical trials showed Mounjaro produced an average weight loss of approximately 20.9% of body weight at the maximum 15 mg dose, whilst Wegovy achieved approximately 14.9% at the maximum 2.4 mg dose — though individual results vary significantly. Both are administered as once-weekly injections using pre-filled pens (Mounjaro's KwikPen or Wegovy's auto-injection pen). Neither medication is injected every 6 days — both follow a strict 7-day dosing schedule. The dual mechanism in Mounjaro may explain the slightly higher average weight loss in SURMOUNT trials compared to STEP trials for Wegovy.
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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?
Eligibility for both Mounjaro and Wegovy in the UK requires a clinical assessment from a GP or prescriber. Both are prescribed for adults with a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, high blood pressure, or cardiovascular disease. Your prescriber will review your medical history, current medications (particularly oral contraceptives, which require additional contraception for 4 weeks after starting Mounjaro), and previous weight loss attempts. Access in the UK is through NHS specialist tier 3 services (with significant regional variation and waiting lists) or private online prescribing following a clinical assessment. Your individual suitability depends on factors like tolerability of side effects, cost, and response to the mechanism — which only a prescriber can assess.
- 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 take Mounjaro every 6 days instead of weekly?
No. Mounjaro must be taken exactly once per week — every 7 days. Taking it every 6 days would alter the prescribed dose schedule and is not recommended. Always follow your prescriber's instructions and the dosing schedule on your KwikPen. If you have concerns about timing, speak to your GP or pharmacist.
What are the key differences between Mounjaro and Wegovy?
Mounjaro (tirzepatide) is a dual GIP+GLP-1 agonist with a maximum dose of 15 mg weekly, whilst Wegovy (semaglutide) is a GLP-1 agonist only with a maximum dose of 2.4 mg weekly. Clinical trials showed Mounjaro produced higher average weight loss (~21% vs ~15%), but both require prescription and clinical assessment. Both are once-weekly injections.
Which medication causes fewer side effects — Mounjaro or Wegovy?
Both have similar common side effects including nausea, diarrhoea, constipation, and stomach pain. Individual tolerance varies — some people experience fewer side effects on one medication than the other. Your prescriber can discuss side effect profiles during your assessment to help choose the best option for you.
How long does it take to see weight loss results with either medication?
Weight loss typically becomes noticeable after 4–8 weeks, with more significant results after 3–4 months of consistent use alongside a reduced-calorie diet and increased physical activity. Clinical trial data showed weight loss continued for up to 68 weeks (Wegovy) and 72 weeks (Mounjaro). Individual timelines vary.
Can I switch from Mounjaro to Wegovy or vice versa?
Switching between medications is possible but must be managed by your prescriber. There is no official conversion chart between tirzepatide and semaglutide — any switch requires a clinical decision and likely involves adjusting doses. Never stop one medication and start another without prescriber guidance.
Ready to take control of your weight loss journey?
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