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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Why Does Mounjaro Make You Feel Cold?
Feeling cold whilst taking Mounjaro is a recognised side effect, though it's less commonly reported than nausea or stomach upset. This happens because tirzepatide affects your body's metabolic rate and how your body regulates temperature. Understanding why this occurs — and how it compares to Wegovy — can help you decide if this medication is right for you. Both Mounjaro and Wegovy are prescription-only weight loss injections available in the UK, but they work through slightly different mechanisms, which can influence side effects differently across individuals.
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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 Affect Body Temperature Differently
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. This dual mechanism can have a more profound effect on metabolic rate than single-pathway medications. When your metabolic rate changes — even temporarily during dose adjustments — your body's thermoregulation can be affected, potentially causing sensations of coldness or chilliness.
Wegovy (semaglutide) is a GLP-1 agonist only, activating a single hormone pathway. Clinical trials from the STEP studies showed that cold sensations are less commonly reported with Wegovy compared to Mounjaro in early dose titration phases. However, individual experiences vary significantly — some people report no temperature changes at all, whilst others notice it across both medications.
- Cold feeling typically occurs during the first 4–8 weeks of Mounjaro treatment
- Often resolves as your body adapts to the medication
- More likely during dose escalation phases (weeks 1–4, 5–8, etc.)
- Not dangerous, but can be uncomfortable — wearing extra layers usually helps
The SURMOUNT clinical trial data for Mounjaro showed that whilst nausea affected over 25% of participants, chilliness was reported less frequently and tended to be mild to moderate in severity.
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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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When to Speak to Your GP and Managing Cold Sensations
If you experience persistent cold sensations that significantly affect your quality of life, contact your GP or the prescriber who issued your Mounjaro prescription. This is important because extreme sensitivity to cold can occasionally indicate other health issues that need attention. Most people find that simple practical steps manage the symptom effectively: wearing warmer clothing, using blankets, staying hydrated, and ensuring adequate nutrition during your adjusted appetite phase.
- Inform your prescriber if coldness is severe or accompanied by other unusual symptoms
- Do not stop taking Mounjaro without medical guidance
- Cold sensations do not mean the medication is working or not working — they're a separate side effect
- Use our free GLP-1 weight loss calculator to track your progress and see if weight loss is occurring despite side effects
Your prescriber may adjust your dose schedule or offer additional guidance based on your individual experience. Remember that individual responses to both Mounjaro and Wegovy vary — what one person experiences may be completely different for another.
- 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 cold a common side effect of Mounjaro?
Feeling cold is a recognised but less common side effect of Mounjaro compared to nausea or stomach upset. It occurs more frequently during the first 4–8 weeks of treatment and during dose escalation phases. Most people find it mild and manageable through wearing extra layers. If it's severe or persistent, contact your prescriber.
Why does Mounjaro cause cold feelings when Wegovy doesn't as often?
Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy is GLP-1 only. This dual mechanism may have a more pronounced effect on metabolic rate and body temperature regulation. However, individual responses vary — some people taking Wegovy also experience coldness, whilst others on Mounjaro don't notice it at all.
Does feeling cold mean Mounjaro is working?
No. Cold sensations are a separate side effect unrelated to weight loss effectiveness. You can experience coldness without losing weight, or lose weight without feeling cold. The two are independent. Use our BMI calculator to track your health metrics objectively rather than relying on side effects as an indicator of progress.
How long does the cold feeling last?
For most people, cold sensations during Mounjaro treatment resolve within 4–8 weeks as your body adapts to the medication. Some people notice it during each dose increase but find it settles quickly. If it persists beyond 12 weeks, contact your GP or prescriber to discuss whether continuing or adjusting your treatment plan is appropriate.
What should I do if I feel very cold whilst taking Mounjaro?
Wear extra layers, use blankets, stay hydrated, and ensure you're eating enough nutrition despite reduced appetite. If coldness is severe, accompanied by shivering you can't control, or comes with other concerning symptoms like chest pain or confusion, seek medical attention. Always inform your prescriber of persistent or severe side effects.
Ready to take control of your weight loss journey?
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