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
Can Mounjaro Cause Cold Symptoms?
If you're taking Mounjaro (tirzepatide), you may wonder whether cold-like symptoms are a known side effect. The short answer is that while Mounjaro can cause fatigue, headaches, and nausea, these are not the same as catching a cold. However, some symptoms may feel similar to early cold or flu signs. Understanding the difference between Mounjaro side effects and genuine illness is important for your health and safety. This guide explains what to expect, when to contact your GP, and how to manage symptoms while using this prescription-only weight management injection in the UK.
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Calculate Your BMI Instantly
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.
Mounjaro Side Effects That May Feel Like Cold Symptoms
Mounjaro is a dual GIP and GLP-1 receptor agonist that works by regulating appetite and supporting weight loss. Common side effects can sometimes feel like cold symptoms, though they are not caused by infection.
- Fatigue and tiredness — listed as a common side effect (affecting up to 1 in 10 people). This can feel similar to the exhaustion of early flu.
- Headaches — reported in clinical practice, sometimes confused with cold-related aches.
- Nausea and stomach upset — very common (affecting more than 1 in 10 people). Nausea is not a typical cold symptom but may accompany general illness feelings.
- Loss of appetite — intentional effect of Mounjaro, but can contribute to general malaise.
These side effects typically appear within the first few weeks of starting Mounjaro or after a dose increase, and often improve as your body adjusts. However, genuine respiratory infections (colds, flu) can still occur while taking Mounjaro — the injection does not prevent infection.
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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.
When to Contact Your GP About Symptoms
If you develop symptoms while taking Mounjaro, your GP can help you determine whether they are medication side effects or a genuine illness. Seek urgent medical attention if you experience:
- High temperature (fever) — not a Mounjaro side effect and suggests infection
- Persistent cough or difficulty breathing — may indicate chest infection
- Severe stomach pain spreading to your back — possible pancreatitis (rare but serious)
- Severe allergic reaction (swelling of face, lips, or throat)
- Symptoms that worsen or do not improve within a few days
Most cold symptoms (sore throat, runny nose, sneezing, cough) are not caused by Mounjaro and indicate a viral or bacterial infection requiring standard self-care or GP advice.
- 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 a runny nose a side effect of Mounjaro?
No, a runny nose, sore throat, and sneezing are not recognised side effects of Mounjaro. These symptoms typically indicate a cold or other respiratory infection, which can occur independently while taking Mounjaro. Standard cold remedies and rest are appropriate. Contact your GP if symptoms persist beyond 7–10 days or worsen.
Can I take cold medicine while using Mounjaro?
Most over-the-counter cold remedies (paracetamol, ibuprofen, cough syrup) are safe to use alongside Mounjaro. However, always check the ingredients and avoid products containing multiple active ingredients. Inform your GP or pharmacist that you're taking Mounjaro, as some medications may affect how oral medicines are absorbed when using Mounjaro.
Does Mounjaro weaken your immune system?
No, Mounjaro does not weaken your immune system. It is a weight management injection that does not directly affect immune function. However, gradual weight management or nutritional deficiencies from reduced calorie intake can theoretically impact immunity, so maintaining adequate nutrition alongside Mounjaro is important.
How long do Mounjaro fatigue side effects last?
Mounjaro-related fatigue typically improves within 2–4 weeks as your body adjusts to the medication. If fatigue persists beyond this period or worsens, contact your GP. Ensure you are eating adequate calories, staying hydrated, and getting enough sleep. Use our free GLP-1 weight loss calculator to check your projected progress and discuss realistic expectations with your prescriber.
Should I stop Mounjaro if I get a cold?
No, you should not stop Mounjaro without medical guidance if you develop a cold. Continue taking your scheduled injection unless your prescriber advises otherwise. If you are severely unwell or hospitalised, inform your healthcare team that you are taking Mounjaro so they can provide appropriate care. Your GP or pharmacist can advise on managing both the cold and your Mounjaro dose.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.