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
Free tracker included with every download this week
Should I Try Mounjaro? A Factual Comparison with Wegovy
Deciding between Mounjaro and Wegovy depends on your individual health profile, not on which is "better"—both are prescription-only UK-licensed weight management medications that work differently. This guide compares the two based on clinical trial data, mechanism of action, dosing, and side effects to help you understand what questions to ask your prescriber. Both require clinical assessment and are used alongside lifestyle changes, not as standalone treatments.
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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, meaning it activates two hormone pathways in the body. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. In the SURMOUNT-1 clinical trial, Mounjaro at its maximum dose (15 mg) showed average weight loss of approximately 20.9% of body weight over 72 weeks. In the STEP-1 trial, Wegovy at 2.4 mg showed average weight loss of approximately 14.9% over 68 weeks. However, individual results vary significantly, and these averages don't predict personal outcomes. Both medications slow gastric emptying and help regulate appetite. The dual mechanism of Mounjaro may theoretically provide additional benefit, but real-world effectiveness depends on how your body responds, which is why your prescriber will assess suitability individually.
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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.
Dosing, Side Effects, and Practical Considerations
Mounjaro starts at 2.5 mg and escalates over 20 weeks to a maximum of 15 mg once weekly. Wegovy starts at 0.25 mg and reaches maximum at 2.4 mg over approximately 16 weeks. Both are once-weekly injections. Side effects are similar for both: nausea, diarrhoea, vomiting, and constipation are most common. Both require a prescription through NHS specialist services or private online prescribing. Your prescriber will consider your medical history, current medications (especially oral contraceptives and diabetes medications), and preferences. Try our GLP-1 weight loss calculator to understand potential outcomes at different doses, and use the BMI calculator to track your baseline and progress throughout treatment.
- 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.
Which medication should I choose—Mounjaro or Wegovy?
Neither you nor your prescriber can predict which will work better for you individually. Both are effective for many people, but response varies. Your prescriber will assess your medical history, current medications, and health goals to recommend the most suitable option. The "best" medication is the one that works for your body and that you can tolerate consistently.
Is Mounjaro more effective because it has a dual mechanism?
Not necessarily for every person. Clinical trials show Mounjaro had numerically higher average weight loss than Wegovy, but individual results vary widely. Some people lose more on Wegovy, some on Mounjaro. Dual mechanism doesn't assures better personal outcomes—individual biology matters most.
How do I access Mounjaro or Wegovy in the UK?
Both are prescription-only and available through NHS specialist tier 3 weight management services (via GP referral) or private online prescribing following a clinical assessment. NHS access varies by region and involves waiting lists in many areas. Private access is faster but involves costs.
Can I switch from Wegovy to Mounjaro or vice versa?
Switching between medications is possible but must be managed by your prescriber. There's no official conversion chart—your prescriber will guide dosing based on your previous dose and response. Never switch without medical supervision.
What if one medication causes side effects I can't tolerate?
Discuss this with your prescriber immediately. Side effects like nausea often ease with time, but if they're severe or persistent, your prescriber may adjust your dose, pause treatment, or switch to the alternative medication. Never stop injections without guidance.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.