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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Mounjaro Cold Symptoms vs Wegovy — What's the Difference?
If you're considering Mounjaro (tirzepatide) or Wegovy (semaglutide) for weight management in the UK, understanding potential side effects including cold-like symptoms is important. Both medications are prescription-only GLP-1 receptor agonists, though Mounjaro uses a dual GIP and GLP-1 mechanism. Cold symptoms are not commonly reported with either medication, but general flu-like sensations can occasionally occur during the adjustment period. Here's how the two compare and what clinical evidence shows about their safety profiles.
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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.
Clinical Trial Data and Side Effect Profiles
Both Mounjaro and Wegovy underwent extensive clinical trials before UK approval. The SURMOUNT-1 trial (Mounjaro) and STEP-1 trial (Wegovy) documented all reported side effects. Neither trial listed common cold or respiratory symptoms as a primary adverse effect with either medication. However, some patients have reported mild flu-like sensations—fatigue, muscle aches, or general malaise—especially during the first few weeks of treatment or when increasing doses. These symptoms typically resolve within days to a week.
- Mounjaro mechanism: Dual GIP and GLP-1 agonist, which may produce different symptom patterns than single-action medications
- Wegovy mechanism: GLP-1 agonist only, used extensively in weight management since 2022
- Most common side effects: Nausea, diarrhoea, constipation, and stomach pain—not respiratory symptoms
- Serious cold-like symptoms: Rare; if you develop high fever, persistent cough, or difficulty breathing, contact your GP immediately
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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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Which Medication Might Be Right for You?
Both Mounjaro and Wegovy require a UK prescription and clinical assessment before starting. Your prescriber will evaluate your medical history, current medications, and weight management goals to determine which is more suitable. Neither medication causes cold or flu in the clinical sense—both are carefully regulated by the MHRA. If you experience any unusual symptoms during treatment, report them to your prescriber rather than stopping medication abruptly. Our GLP-1 weight loss calculator can help you explore potential weight management outcomes with either medication, while your GP or specialist will make the personalised treatment recommendation. Individual responses vary significantly, so what works for one person may differ 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.
Can Mounjaro cause cold symptoms or flu-like illness?
Cold symptoms are not a recognised side effect of Mounjaro in clinical trials. Some patients report mild flu-like sensations (fatigue, muscle aches) during the first weeks or dose increases, which usually resolve within a week. True cold or respiratory infection requires medical attention; contact your GP if symptoms persist.
Does Wegovy cause cold-like symptoms?
No, Wegovy is not documented to cause cold symptoms. Flu-like sensations are also uncommon. The most frequent side effects are gastrointestinal—nausea, diarrhoea, constipation. Any persistent respiratory symptoms should be reported to your GP, as they may indicate a separate infection.
Why might someone feel flu-like on Mounjaro or Wegovy?
Mild flu-like sensations during the first weeks may relate to the body's adjustment to the medication and changes in appetite or digestion. This is distinct from actual infection. Staying hydrated, eating small regular meals, and resting typically help. Contact your GP if symptoms worsen or last more than a week.
If I develop a real cold while taking Mounjaro or Wegovy, is it safe to continue?
Yes, you can continue either medication if you develop a common cold. However, if you're unable to eat or drink due to illness, discuss temporary dose adjustments with your prescriber. Do not stop medication abruptly—always consult your GP or specialist before making changes.
How do I know if my symptoms are the medication or an actual infection?
Medication-related symptoms are usually mild, appear in the first 1–2 weeks or after a dose increase, and resolve within days. True infection symptoms include high fever (38°C+), persistent productive cough, sore throat, or difficulty breathing. If in doubt, contact your GP or call NHS 111 for guidance.
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