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
Why Am I So Cold On Mounjaro?
Feeling unusually cold whilst taking Mounjaro (tirzepatide) is a recognised side effect that some people experience, particularly during the dose titration phase. This happens because Mounjaro affects how your body regulates temperature and energy metabolism. Understanding why this occurs, how long it typically lasts, and when to seek help from your GP can help you manage the experience effectively whilst on this prescription weight management medication.
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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 Affects Body Temperature
Mounjaro is a dual GIP and GLP-1 receptor agonist that works by altering appetite regulation and slowing gastric emptying. As a side effect of these metabolic changes, some people report feeling cold or experiencing chills, particularly when first starting the medication or increasing their dose. This temperature sensitivity can occur because tirzepatide influences how your body burns energy and regulates metabolism.
- Metabolic changes: The medication alters how efficiently your body uses calories, which can affect thermogenesis (heat generation)
- Reduced food intake: Eating significantly less food means your body generates less internal heat during digestion
- Individual variation: Not everyone experiences this side effect — sensitivity varies based on genetics, starting weight, and dose level
If you're prescribed Mounjaro through the NHS or privately following a clinical assessment, your prescriber should have discussed potential side effects. This side effect is usually temporary and tends to improve as your body adjusts to the medication.
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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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Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Managing Cold Feelings And When To Contact Your GP
In most cases, feeling cold on Mounjaro resolves within a few weeks as your body adapts to the medication. Practical steps include wearing layered clothing, staying active (which generates body heat), and maintaining adequate nutrition despite reduced appetite. If you experience severe chills, fever, or persistent cold sensations lasting more than a few weeks, contact your GP to rule out other causes and discuss whether dose adjustment might help.
Keep track of when cold feelings occur using our free progress tracker — this information helps your prescriber assess whether the symptom is related to dose increases or other factors. Most people find the symptom manageable and temporary, though everyone's experience with Mounjaro differs. Your GP can provide personalised guidance based on your individual response to the medication.
- 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 not listed as a "very common" side effect in clinical trials, but it is reported by some people using Mounjaro in real-world practice. It's less frequent than nausea or constipation, but can occur at any dose during titration. If it's bothersome, mention it to your GP or prescriber.
Why does Mounjaro make you feel cold?
Mounjaro alters your metabolism and reduces hunger, meaning you eat less food. Eating generates heat through digestion (thermogenesis), so eating significantly less can lower your body temperature. The medication's effect on your metabolic rate may also contribute.
How long does the cold feeling last on Mounjaro?
Most people find the cold sensation resolves within 2–4 weeks as their body adjusts to the medication. However, this varies individually. If it persists beyond a month or worsens, contact your GP to discuss whether your dose needs adjustment.
What should I do if I feel very cold on Mounjaro?
Wear warm layers, stay physically active, ensure you're eating enough protein and calories despite reduced appetite, and stay hydrated. If the cold is severe, accompanied by fever, or doesn't improve in a few weeks, contact your GP for advice.
Does feeling cold mean Mounjaro isn't working?
No. Feeling cold and weight loss are separate responses to the medication. Some people lose weight without feeling cold, others experience both. The cold sensation does not indicate whether the medication is helping you lose weight — discuss your progress with your prescriber.
Ready to take control of your weight loss journey?
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