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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Feeling Hot on Mounjaro vs Wegovy — What's the Difference?
Feeling unusually hot is not a commonly reported side effect of either Mounjaro or Wegovy, but both weight loss injections can affect body temperature regulation and metabolism. While this symptom is rare, understanding how Mounjaro (tirzepatide) and Wegovy (semaglutide) differ may help you and your prescriber decide which medication is most suitable for you. This guide compares the two medications, their mechanisms, trial data, and what the evidence shows about thermoregulation effects.
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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 Differ in Mechanism and Trial Data
Mounjaro and Wegovy are both once-weekly weight loss injections available in the UK, but they work differently. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1-only agonist, activating a single pathway.
In the SURMOUNT-1 clinical trial, Mounjaro participants lost an average of 20.9% body weight at the maximum 15 mg dose. In the STEP-1 trial, Wegovy participants lost approximately 14.9% body weight at the maximum 2.4 mg dose. Both trials ran alongside reduced-calorie diets and increased physical activity. Feeling unusually hot was not listed as a very common or common side effect in either trial — nausea, diarrhoea, and stomach pain were the most frequent effects reported. Individual experience varies significantly, and your prescriber will assess which medication suits your health profile.
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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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Individual Suitability and Prescriber Assessment
Neither Mounjaro nor Wegovy can be recommended to you personally without clinical assessment. Both are prescription-only medications requiring assessment by a UK-licensed prescriber. Your prescriber will review your medical history, current medications, BMI, and any weight-related health conditions to determine which, if either, is appropriate for you.
If you experience feeling unusually hot whilst on either medication, contact your GP or prescriber immediately — this could indicate an underlying issue or an unusual reaction requiring investigation. Use our free GLP-1 weight loss calculator to explore potential outcomes, and our BMI calculator to understand your current health status context alongside any medication consideration.
- 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.
Is feeling hot a side effect of Mounjaro?
Feeling hot is not listed as a common side effect in clinical trials of Mounjaro. The most frequent side effects are nausea, diarrhoea, vomiting, and constipation. If you experience persistent or unusual heat sensation on Mounjaro, contact your GP or prescriber immediately, as this could indicate a separate health issue or an unusual reaction.
Does Wegovy cause you to feel hot?
Feeling hot is not a reported common side effect of Wegovy. Like Mounjaro, the most frequent side effects in clinical trials were gastrointestinal — nausea, diarrhoea, and constipation. Any unusual body temperature changes should be discussed with your healthcare provider.
What are the most common side effects of both Mounjaro and Wegovy?
The most common side effects reported in clinical trials for both medications include nausea, diarrhoea, vomiting, constipation, and abdominal pain. These are typically mild to moderate and often improve as the body adjusts. Very serious side effects like severe pancreatitis are rare but require immediate medical attention.
Can changes in metabolism from weight loss cause feeling hot?
Yes, significant weight loss and metabolic changes can occasionally affect how your body regulates temperature. This is not specific to these medications but can occur with any substantial weight loss. If this persists or is uncomfortable, speak to your GP to rule out other causes like thyroid changes or infection.
How do I decide between Mounjaro and Wegovy in the UK?
You cannot choose between them yourself — your prescriber will assess your individual health situation and recommend the most suitable option based on your BMI, medical history, and any weight-related conditions. Both require a clinical assessment before prescription, whether through NHS specialist services or private prescribing with a licensed UK prescriber.
Ready to take control of your weight loss journey?
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