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 and Asthma — What You Need to Know
If you have asthma and are considering Mounjaro (tirzepatide) for weight management, it's important to understand how this medication may interact with your respiratory health. Mounjaro is a prescription-only GIP and GLP-1 receptor agonist, different from Wegovy which is a GLP-1 agonist only. Both require clinical assessment before prescription. This guide explains the key differences between Mounjaro and Wegovy specifically for asthma sufferers, and what your GP should consider when assessing your suitability for treatment.
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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.
Mounjaro vs Wegovy — Key Mechanism and Trial Differences
Mounjaro (tirzepatide) works as a dual GIP and GLP-1 receptor agonist, activating two natural hormone pathways to regulate appetite and food intake. Clinical trials (SURMOUNT-1) showed average weight loss of approximately 15–21% of body weight depending on dose escalation, alongside reduced-calorie diet and increased physical activity.
Wegovy (semaglutide) is a single GLP-1 receptor agonist with a different mechanism — it works through one hormone pathway. STEP trial data showed average weight loss of approximately 14.9% body weight on the maximum 2.4mg dose.
- Mounjaro doses: 2.5mg to 15mg once weekly
- Wegovy doses: 0.25mg to 2.4mg once weekly
- Both require a minimum 4-week period at each dose before escalation
- Both are UK KwikPen pre-filled injection devices
Neither medication is insulin and both may cause similar gastrointestinal side effects like nausea and diarrhoea. Individual results vary significantly based on lifestyle, genetics, and adherence.
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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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Asthma Considerations — Which Medication May Be Suitable for You
If you have asthma, your prescriber will assess whether either Mounjaro or Wegovy is appropriate during your clinical evaluation. Neither medication directly treats or worsens asthma, but both can cause side effects that may affect respiratory comfort — particularly nausea, which can indirectly impact breathing if severe.
Importantly, Mounjaro's dual GIP+GLP-1 mechanism may theoretically affect gastric function differently than Wegovy's single GLP-1 pathway, though clinical evidence specific to asthma sufferers is limited. Your GP or prescriber will review your asthma control, current medications (especially if you take oral contraceptives or diabetes drugs), and medical history to decide which — if either — is clinically suitable for you.
Always disclose your asthma diagnosis and current asthma medications when seeking prescription weight loss treatment. Both medications require a clinical assessment, and your prescriber will make an individualised recommendation.
- 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.
Does Mounjaro affect asthma or make it worse?
Mounjaro itself does not directly affect asthma or airways. However, nausea and stomach side effects can occasionally indirectly impact breathing comfort. Always inform your prescriber about your asthma before starting treatment. Individual responses vary, and your GP will assess whether it's suitable for you.
Is Wegovy safer than Mounjaro if I have asthma?
Neither is "safer" — both require the same clinical assessment. Wegovy uses a single GLP-1 mechanism while Mounjaro uses a dual GIP+GLP-1 mechanism. Evidence specific to asthma sufferers is limited. Your prescriber will recommend which — if either — is appropriate based on your individual health profile.
Can I take Mounjaro or Wegovy alongside my asthma inhalers?
Weight loss medications do not typically interact with standard asthma inhalers (salbutamol, ICS). However, always list all your medications — including inhalers and preventers — when seeking assessment. Your prescriber will check for specific interactions based on your full medication list.
What's the difference between Mounjaro's GIP+GLP-1 and Wegovy's GLP-1?
Mounjaro activates two hormone pathways (GIP and GLP-1); Wegovy activates one (GLP-1 only). This dual action may contribute to Mounjaro's slightly higher average weight loss in trials, but individual results vary. Both work similarly on appetite regulation and require clinical assessment before prescription.
How do I get assessed for Mounjaro or Wegovy if I have asthma?
Contact your GP or a UK-licensed prescriber through NHS specialist weight management services or private online assessment. You'll undergo a clinical evaluation including your asthma history. Be honest about asthma control, current medications, and any respiratory concerns. Your GP will then recommend whether either medication is suitable for you.
Ready to take control of your weight loss journey?
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