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 and Appetite Loss — How It Compares to Wegovy
Reduced appetite is one of the most commonly reported experiences when taking Mounjaro for weight management. Many UK adults ask whether Wegovy causes similar appetite suppression, and the answer lies in how these two medications work differently. Both are prescription-only injections used alongside diet and activity changes, but their mechanisms differ. This guide compares appetite effects between Mounjaro (tirzepatide) and Wegovy (semaglutide), explains why reduced eating happens, and helps you understand what to expect so you can make an informed decision with your prescriber.
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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.
How Mounjaro and Wegovy Work — and Why Appetite Changes
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways. GLP-1 signals fullness to the brain and slows how quickly food leaves the stomach, while GIP helps regulate appetite and glucose handling. This dual action may produce stronger appetite suppression in many people.
Wegovy is a GLP-1 receptor agonist only — it activates just the GLP-1 pathway. Clinical trial data from SURMOUNT showed Mounjaro produced average weight loss of around 20.9% at the highest dose, whilst Wegovy (STEP trials) showed approximately 14.9% at maximum dose. The appetite-reducing effect tends to be more pronounced with Mounjaro, though individual responses vary significantly.
When you can't eat normally on either medication, it's usually because:
- The brain receives stronger "fullness" signals after small amounts of food
- Food moves slowly through your stomach, creating prolonged satisfaction
- Natural appetite hormones are being suppressed
- Nausea or indigestion may make eating uncomfortable
This effect typically appears within the first few weeks and may decrease over time as your body adjusts, though some people maintain reduced appetite throughout treatment. Your prescriber can adjust your dose if appetite loss becomes problematic.
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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 Will Consider
Both Mounjaro and Wegovy require a UK prescription and clinical assessment before you can begin. Your prescriber will ask about your medical history, current medications, and how different side effects might affect you. If you've struggled with nausea or appetite loss in the past, mention this — it helps guide which medication might suit you better.
Neither medication is "better" — suitability is personal. Some people find Mounjaro's stronger appetite suppression helpful and tolerate it well. Others prefer Wegovy's single mechanism. Some find the appetite loss on either medication too severe and need dose adjustment or may switch to the other option.
Try our free GLP-1 weight loss calculator to explore projected outcomes at different doses, and use the BMI calculator to check your starting point. This context helps you ask informed questions during your clinical assessment appointment.
- 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.
Does Mounjaro cause more appetite loss than Wegovy?
In clinical trials, Mounjaro (dual GIP+GLP-1) produced stronger average weight loss than Wegovy (GLP-1 only), suggesting appetite suppression is typically more pronounced. However, individual responses vary — some people experience similar appetite changes on either medication, whilst others find one suits them better. Your prescriber will help identify which is more appropriate for you based on your personal tolerance.
Why can't I eat when taking Mounjaro?
Mounjaro activates appetite-regulating hormones (GIP and GLP-1) that signal fullness to your brain and slow gastric emptying. This means you feel satisfied after smaller amounts of food. In clinical trials, reduced appetite was one of the most common side effects. It usually improves after the first few weeks as your body adjusts, but discuss persistent appetite loss with your prescriber.
Is appetite loss on Mounjaro dangerous?
Mild appetite reduction is intentional and expected — it supports weight loss. However, if you can't eat enough to maintain basic nutrition or hydration, contact your GP immediately. Severely restricted eating can lead to deficiencies. Your prescriber may lower your dose or switch medications if appetite suppression is too severe. Never skip meals entirely without medical guidance.
Can I switch from Mounjaro to Wegovy if I can't eat?
Yes — if Mounjaro's appetite suppression is unmanageable, your prescriber may consider switching to Wegovy (GLP-1 only), which typically produces milder appetite loss. However, any medication change must be managed by your prescriber. They'll assess whether adjusting your current dose, switching medications, or a temporary break is safest. Always discuss concerns with them before making changes.
When does appetite loss on Mounjaro start and stop?
Appetite suppression often appears within the first 1–2 weeks and is most pronounced during dose escalation. Many people find it settles after 4–6 weeks as their body adapts. Some retain reduced appetite throughout treatment — this isn't harmful if you're eating adequate nutrition. If appetite loss interferes with eating, notify your prescriber; dose adjustment may help.
Ready to take control of your weight loss journey?
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