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 Do You Feel On Mounjaro vs Wegovy?
When starting a weight management injection like Mounjaro (tirzepatide) or Wegovy (semaglutide), you may wonder what the experience will actually feel like. Both are prescription-only GLP-1-based medications, but they work through different mechanisms and people's experiences vary significantly. Understanding what to expect — from appetite changes to potential side effects — can help you make an informed decision with your prescriber. This guide compares how users typically feel on each medication based on clinical trial data and real-world experience.
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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.
Clinical Trial Data: What the Evidence Shows
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways rather than one. In the SURMOUNT-1 clinical trial, the most commonly reported feelings were reduced appetite and early fullness — users felt satisfied with smaller portions. Nausea was very common, especially in the first 4–8 weeks, but typically improved as the body adjusted. Gastrointestinal changes (diarrhoea or constipation) were frequently reported.
Wegovy (semaglutide) is a single GLP-1 receptor agonist. In the STEP-1 clinical trial, users reported similar experiences: reduced hunger, feeling fuller faster, and decreased food cravings. Nausea was also very common early on but usually diminished over time. Gastrointestinal effects were comparable to Mounjaro, though individual experiences varied widely.
- Both medications typically require 4 weeks per dose level before increasing
- Side effects often peak during dose escalation weeks then settle
- Results vary significantly between individuals — some feel minimal changes, others feel substantial appetite suppression
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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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Practical Differences: What You'll Actually Notice
The key difference in how you feel comes down to mechanism: Mounjaro's dual action may produce stronger appetite suppression in some people, but this isn't assured or universal. Some users report that Mounjaro feels more potent; others experience similar sensations on both. Early weeks are typically the hardest — nausea, changes in taste preference, and reduced appetite can feel overwhelming. Most people adjust within 2–3 months.
Your prescriber will start you on the lowest dose and increase gradually (dose titration), which helps your body adapt. You'll also be encouraged to use our GLP-1 weight loss calculator to track projected progress and monitor how you're responding. Keeping a simple food and symptom diary can help you identify what you can comfortably eat and when side effects are worst. Individual suitability depends on your health history, other medications, and how your body responds — only your GP or prescriber can assess this.
- 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.
Will I feel sick on Mounjaro or Wegovy?
Nausea is very common, especially in the first 4 weeks after starting or increasing your dose. Most people find it improves significantly by weeks 3–4 as their body adjusts. Taking your injection at night and eating small, bland meals can help. If nausea persists beyond 6–8 weeks, speak to your prescriber — they may recommend dose adjustment or additional support.
How long before I feel the appetite suppression?
Most people notice reduced appetite within 3–5 days of their first injection. However, the effect strengthens with each dose increase. Full appetite suppression typically builds over 4–12 weeks as you progress through the dose titration schedule. Individual timelines vary — some feel dramatic changes immediately, others experience more gradual shifts.
Will I feel different on Mounjaro compared to Wegovy?
Both medications produce similar overall sensations — reduced hunger, early fullness, and potential nausea. Mounjaro's dual mechanism may feel slightly more potent to some users, but clinical trials show comparable average weight loss. Your individual experience depends more on your body's response than which medication you choose. Your prescriber will help decide which suits you.
Can I eat normally on these medications?
Most people can still eat normally, but portions naturally become smaller because you feel fuller faster. Some users find they lose interest in certain foods, especially very sweet or greasy items. This appetite regulation is how the medication works. You should still aim for balanced nutrition with adequate protein, vegetables, and fluids — your GP can refer you to a dietitian for personalised guidance.
What if I feel too many side effects?
Side effects are usually temporary and often improve with time. However, if you're struggling significantly, contact your prescriber immediately — never stop the medication suddenly. Your prescriber may recommend dose adjustment, timing changes (morning vs evening), or dietary modifications. If side effects persist beyond reasonable adjustment, switching medications may be considered, though this requires clinical assessment.
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.