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 Mounjaro and Wegovy Affect Your Meals
Both Mounjaro and Wegovy are prescription weight management injections used in the UK, but they work through different mechanisms that affect how you eat and experience meals. Mounjaro (tirzepatide) uses a dual GIP and GLP-1 approach, while Wegovy (semaglutide) activates GLP-1 alone. Understanding these differences helps explain why meal sizes, appetite, and eating patterns may vary between the two medications. Your GP or prescriber can assess which is more suitable for your individual needs following a clinical assessment.
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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.
Mechanism Differences and Meal Effects
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may influence appetite differently than Wegovy. The GIP component targets additional appetite regulation pathways, which may intensify feelings of fullness and reduce food cravings during meals.
Wegovy (semaglutide) activates GLP-1 alone, signalling satiety to the brain and slowing how quickly food leaves your stomach. Both medications reduce meal sizes, but clinical trial data suggests Mounjaro users reported slightly greater appetite suppression overall.
- Mounjaro: average ~clinically studied weight loss (SURMOUNT-1 trial, 15 mg dose)
- Wegovy: average ~clinically studied weight loss (STEP-1 trial, 2.4 mg dose)
- Individual meal tolerance varies significantly between users
Neither medication is assured to work the same way for every person — genetics, baseline appetite, and lifestyle factors all play a role.
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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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Choosing Between Them — What Your Prescriber Considers
Both Mounjaro and Wegovy require a prescription following clinical assessment by a UK-licensed prescriber. Your prescriber will consider your medical history, current medications, and whether you're eligible under NICE guidance. Use our free GLP-1 weight loss calculator to estimate potential outcomes at different doses for either medication — this can inform discussions with your prescriber.
Eligibility is the same for both: a BMI of 30 kg/m² or above, or 27–29.9 kg/m² with weight-related health conditions such as type 2 diabetes, hypertension, or sleep apnoea. Your prescriber may recommend one over the other based on your specific circumstances, not on meal preference alone.
- 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 Mounjaro reduce my meal sizes more than Wegovy?
Clinical trials suggest Mounjaro users experienced slightly greater appetite suppression, but individual results vary significantly. Both reduce meal sizes substantially for most users. Your personal response depends on genetics, baseline appetite, and other factors. Only a clinical assessment can predict your likely response.
How quickly do Mounjaro and Wegovy affect meal sizes?
Both medications take effect within days of the first dose, though appetite suppression typically intensifies over the first 4 weeks as your body adjusts. Meal sizes usually decrease noticeably within the first 1–2 weeks for most users. Changes continue as you escalate doses.
Can I switch from Wegovy to Mounjaro if meal effects aren't right?
Switching between medications requires prescriber guidance. There is no official conversion chart between Mounjaro and Wegovy doses. Any switch must be managed carefully by your prescriber to ensure safe dosing and monitor your response.
Which medication has fewer meal-related side effects?
Both cause similar gastrointestinal side effects: nausea, diarrhoea, constipation, and abdominal discomfort are common. These typically improve over time as your body adjusts. There is no clear evidence that one causes significantly fewer meal-related side effects than the other.
What if neither medication helps my meal sizes reduce?
Not all users respond equally to GLP-1 or GIP/GLP-1 medications. If appetite suppression is minimal after several weeks at therapeutic dose, discuss alternative approaches with your prescriber. Sustained weight loss requires medication plus reduced-calorie diet and increased physical activity.
Ready to take control of your weight loss journey?
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