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 is an uncommon but reported side effect of Mounjaro (tirzepatide), a prescription weight loss injection used in the UK. While not listed as a very common side effect in the official information, some people report experiencing chilliness or cold sensitivity during treatment. This guide explains what causes this feeling, how common it is, and when to speak to your GP about managing it alongside your weight loss journey.
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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 May Affect Body Temperature
Mounjaro works as a dual GIP and GLP-1 receptor agonist, which means it activates two natural hormone pathways to regulate appetite and support weight management. As your body adjusts to tirzepatide and begins losing weight, several mechanisms may contribute to feeling cold:
- Reduced calorie intake: When you eat fewer calories alongside Mounjaro treatment, your metabolic rate can decrease slightly, which may make you feel colder than usual
- Decreased body fat: As weight loss progresses, you have less natural insulation, making you more sensitive to cold temperatures
- Metabolic changes: GLP-1 and GIP activation may influence how your body regulates temperature as it adapts to the medication
- Dose adjustment: Some people report this effect more prominently during dose titration periods when the body is adjusting to increasing doses
If you're taking Mounjaro via a KwikPen and experiencing persistent cold sensitivity, keep track of when it occurs—this information will help your prescriber assess whether it's related to the medication or other factors like diet or activity level.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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Accessing Mounjaro in the UK — NHS vs Private Routes
In the UK, Mounjaro is available through NHS specialist weight management services and private prescription routes. Accessing it depends on your circumstances: through the NHS, you'll need referral to a tier 3 or tier 4 weight management service from your GP, though waiting times vary significantly by region and ICB. Privately, you can obtain a prescription following an online consultation with a UK-licensed prescriber without an NHS referral. Both routes require clinical assessment to confirm you meet Mounjaro eligibility criteria—typically a BMI of 30 or above, or 27–29.9 with weight-related health conditions. Your prescriber will also discuss potential side effects like feeling cold and help you manage them alongside your treatment plan.
- 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 Mounjaro's official information, but some people do report it during treatment. It's more likely linked to gradual weight management and reduced calorie intake rather than tirzepatide itself. If you experience persistent cold sensitivity, mention it to your GP or prescriber.
How can I manage feeling cold while taking Mounjaro?
Layer your clothing, keep warm drinks nearby, and ensure you're eating enough calories for your activity level. Some cold sensitivity naturally decreases as your body adjusts to the medication. If it's severe or persistent, your prescriber may adjust your dose or review your diet to ensure adequate nutrition.
Will feeling cold go away after I stop Mounjaro?
Yes, cold sensitivity typically resolves once you stop the medication and your metabolic rate stabilizes. As you maintain your weight loss through diet and exercise, your body also naturally acclimates. Most people find this side effect fades within weeks of discontinuing treatment.
Should I tell my GP if Mounjaro makes me feel cold?
Yes, absolutely. Always report any side effects to the prescriber managing your Mounjaro treatment, even if they seem minor. Your GP can assess whether it's medication-related, nutritional, or linked to your weight loss pace, and help adjust your treatment plan if needed.
Does Mounjaro vs Wegovy make a difference to feeling cold?
Both Mounjaro and Wegovy can theoretically contribute to cold sensitivity through similar mechanisms—reduced calories, weight loss, and metabolic adjustment. Wegovy (semaglutide) is a GLP-1 agonist only, whereas Mounjaro is dual GIP+GLP-1, but both work by reducing appetite. Individual responses vary greatly regardless of which medication you're taking.
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