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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When Should You Start Mounjaro? Mounjaro vs Wegovy
Deciding whether to start Mounjaro (tirzepatide) now or consider alternatives like Wegovy depends on your individual health profile, BMI, and weight-related conditions. Both are prescription-only GLP-1 and GIP/GLP-1 medications available in the UK, but they differ in mechanism, dosing, and clinical evidence. This guide compares both to help you understand what a prescriber might consider when recommending timing and choice of medication.
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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 Compare: Clinical Evidence and Mechanism
Mounjaro (tirzepatide) and Wegovy (semaglutide) work through different pathways. Mounjaro is a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways to regulate appetite and blood sugar. Wegovy is a GLP-1 agonist only, activating a single pathway. In clinical trials, Mounjaro showed average weight loss of approximately 15–21% of body weight in the SURMOUNT trials, while Wegovy demonstrated around 15% in the STEP-1 trial. Both results were achieved alongside a reduced-calorie diet and increased physical activity. Individual results vary significantly. Your GP or prescriber will assess your mounjaro eligibility uk based on your BMI — typically 30 or above, or 27–29.9 with weight-related health conditions like type 2 diabetes, hypertension, or sleep apnoea. Use our free BMI calculator to check your BMI instantly and understand where you fall on NHS guidelines.
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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.
Timing and Suitability: Which Should You Start?
The "best time" to start either medication depends on your readiness, health conditions, and prescriber assessment. Mounjaro may be considered first if you have type 2 diabetes or metabolic factors that benefit from dual GIP/GLP-1 action, or if you want once-weekly mounjaro kwikpen dosing. Wegovy may suit those preferring established single-pathway evidence or who have already tolerated GLP-1 therapy. Both require mounjaro uk prescription through NHS specialist services or private prescribing following clinical assessment. Timing also depends on NHS availability in your area — many regions have waiting lists. Your prescriber will discuss mounjaro dose titration schedules (Mounjaro starts at 2.5 mg, Wegovy at 0.25 mg) and help you prepare with diet and exercise changes. Neither is a structured approach — both require sustained lifestyle support.
- 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 switch from Wegovy to Mounjaro?
Yes, switching is possible under prescriber guidance. There is no official conversion chart, but approximate equivalence exists (e.g., Wegovy 2.4 mg roughly corresponds to Mounjaro 15 mg). Any switch requires medical supervision, dose adjustment, and monitoring. Your prescriber will decide timing based on your response and tolerance to your current medication.
What makes Mounjaro different from Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist (two hormones), while Wegovy is a GLP-1 agonist only (one hormone). This dual mechanism may explain Mounjaro's slightly higher average weight loss in trials. Both are once-weekly injections, but Mounjaro starts at 2.5 mg and titrates to 15 mg, while Wegovy starts at 0.25 mg and reaches 2.4 mg maximum.
How do I know if I'm eligible for Mounjaro or Wegovy?
Both require a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Use our free BMI calculator to check your BMI. Eligibility is assessed individually by a prescriber following clinical assessment. Your GP can refer you to NHS specialist weight management services, or you can pursue private prescribing options.
What are the main side effects of Mounjaro compared to Wegovy?
Both share similar side effects: nausea, diarrhoea, vomiting, constipation, and stomach pain are very common. Both are generally well-tolerated. The SURMOUNT and STEP trials showed comparable side effect profiles. Individual tolerance varies. Discuss mounjaro side effects uk specific concerns with your prescriber.
Is Mounjaro available on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is approved by NICE for weight management in NHS specialist tier 3 services. However, availability and waiting times vary significantly by region and ICB. Private prescribing is widely available. Your GP can advise on NHS access in your area or you can explore private options through registered UK pharmacies.
Ready to take control of your weight loss journey?
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