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
What Does Mounjaro Feel Like — What to Expect
Mounjaro (tirzepatide) is a prescription-only weight management injection that works by activating two natural hormone pathways: GIP and GLP-1. Most people experience a significant reduction in appetite and changes to how full they feel after eating. The sensation of using Mounjaro varies between individuals — some notice effects within days, while others take weeks. Common experiences include feeling less interested in food, reduced cravings, and earlier satiety. Understanding what to expect can help you prepare for your weight loss journey with this UK-licensed 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 Feels — Common Sensations
When you start Mounjaro, the most noticeable sensation for many people is reduced appetite. This isn't a sudden feeling of sickness — it's more that food becomes less appealing and you feel satisfied after smaller portions. Many users describe it as a natural loss of interest in food rather than a forced restriction.
During the first week on the starting dose (2.5 mg), you might experience:
- Mild nausea (very common, especially after meals)
- Changes in taste preferences
- Reduced cravings for sweet or fatty foods
- Feeling fuller sooner than usual
These sensations typically settle as your body adjusts over the first 4 weeks. At higher doses (10 mg, 15 mg), appetite suppression becomes more pronounced. The dual GIP and GLP-1 mechanism of tirzepatide (unlike single-mechanism GLP-1 alternatives such as Wegovy or semaglutide) may create a stronger overall appetite reduction for some individuals, though results vary significantly.
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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.
Side Effects You Might Feel — What's Normal
Nausea is the most commonly reported sensation in the first few weeks. It's usually mild to moderate and improves as your body adjusts. Eating smaller, regular meals and staying hydrated can help. Stomach discomfort and changes in digestion (constipation or diarrhoea) are also common and typically resolve within 4–8 weeks as your dose stabilises.
Some people experience fatigue or dizziness when starting Mounjaro, particularly if they're reducing food intake significantly. This usually passes. Importantly, if you experience severe stomach pain, persistent vomiting, or signs of allergic reaction (swelling of face or lips), contact your GP or NHS 111 immediately. Most side effects are manageable, and many users report that reduced appetite far outweighs the temporary discomfort. Track your progress and how you feel using a progress tracker to monitor your individual response.
- 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 hurt when injected?
The injection itself is usually painless or minimally uncomfortable. The needle is very small (similar to insulin pens), and most people describe it as a quick prick. Injection site reactions like mild redness or bruising can occur but are uncommon. Rotating injection sites between your stomach, thigh, and upper arm helps prevent irritation.
How quickly will I feel Mounjaro working?
Most people notice reduced appetite within 2–7 days of their first injection, though some take up to 2 weeks. The effects become more pronounced as your dose increases (you increase every 4 weeks). Individual response varies — some people feel dramatic appetite suppression immediately, others notice gradual changes over several weeks. Consistency is important; effects build over time.
Will Mounjaro make me feel sick all the time?
Nausea is very common initially but temporary for most people. It's usually mild and improves significantly within 4–8 weeks as your body adjusts. Eating smaller meals, avoiding greasy foods, and staying hydrated help manage nausea. If it persists beyond 8 weeks or becomes severe, speak to your prescriber — they may adjust your approach or dose timing.
Can I feel Mounjaro working on my blood sugar?
Yes, if you have type 2 diabetes or prediabetes. Mounjaro helps regulate blood sugar, and you may notice improved energy levels and reduced sugar cravings. If you're also taking diabetes medication (like insulin or sulphonylureas), your prescriber will monitor your blood sugar carefully — doses may need adjusting to prevent low blood sugar.
What's the difference between how Mounjaro and Wegovy feel?
Both reduce appetite, but Mounjaro's dual GIP and GLP-1 mechanism may produce stronger appetite suppression for some people compared to Wegovy (semaglutide, GLP-1 only). Nausea profiles are similar. Individual experience is highly variable — some feel more suppression with one, others notice no difference. Your prescriber can discuss which might suit you better based on your health profile and response. ```
Ready to take control of your weight loss journey?
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