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 Heart Palpitations vs Wegovy
Heart palpitations are a reported side effect with both Mounjaro and Wegovy, though they are relatively uncommon in clinical trials. This guide explains how the two medications differ in mechanism, what the evidence shows about cardiac symptoms, and how your GP or prescriber will assess which is more suitable for you. Both are prescription-only weight management injections licensed in the UK, and individual suitability depends on your personal health profile and medical history. Understanding the differences between Mounjaro (tirzepatide), a dual GIP and GLP-1 receptor agonist, and Wegovy (semaglutide), a GLP-1 agonist only, can help you have an informed conversation with your healthcare provider.
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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 Do Mounjaro and Wegovy Differ in Mechanism?
Mounjaro (tirzepatide) activates two hormone pathways: GIP (glucose-dependent insulinotropic polypeptide) and GLP-1 (glucagon-like peptide-1). This dual mechanism may affect heart rate and cardiovascular function differently than GLP-1 alone. Wegovy (semaglutide) activates only the GLP-1 pathway.
In clinical trials, heart palpitations were reported by a small percentage of participants on both medications. For Mounjaro in the SURMOUNT-1 trial, palpitations were uncommon. For Wegovy in the STEP trials, reported rates were similarly low. However, individual responses vary.
The dual mechanism of Mounjaro may theoretically carry a different cardiovascular risk profile than GLP-1 alone, which is why prescribers will assess your personal cardiac history before recommending either medication. If you have a history of arrhythmia, heart disease, or heart rate changes, your GP will need this information to determine suitability. Your prescriber will consider your full medical picture, not just weight and BMI.
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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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What Does the Evidence Show About Heart Symptoms?
Clinical trial data shows heart palpitations are not common side effects with either medication, though they have been reported. Both Mounjaro and Wegovy carry warnings about potential heart rate changes, particularly in people with underlying cardiac conditions.
gradual weight management itself can affect heart function, and both medications are used alongside reduced-calorie diets and increased physical activity, which also influence cardiovascular function. Your GP will want to know if you experience new palpitations, chest discomfort, shortness of breath, or unusual heart rate changes while on either medication.
If you develop cardiac symptoms after starting a GLP-1 or GIP/GLP-1 medication, contact your prescriber immediately. These symptoms require urgent assessment and may mean the medication is not suitable for you. Your prescriber may switch you to the alternative, adjust your dose, or recommend stopping treatment.
- 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 I use MyWeightCheck tools to help assess if GLP-1 medication is right for me?
MyWeightCheck provides a free BMI calculator to check your personal BMI, which is one eligibility criterion for prescription weight loss treatment. However, BMI alone does not determine suitability—your GP or prescriber will assess your full medical history, including any cardiac symptoms or heart conditions, before recommending Mounjaro or Wegovy.
How common are heart palpitations with Mounjaro vs Wegovy?
Heart palpitations were rare in both SURMOUNT and STEP clinical trials. They are listed as uncommon side effects for both medications. However, individual responses vary. If you have pre-existing heart conditions or arrhythmia, your prescriber will take extra care assessing suitability.
What should I do if I develop heart palpitations while on Mounjaro or Wegovy?
Contact your GP or prescriber immediately. Heart palpitations, chest pain, shortness of breath, or irregular heartbeat require urgent assessment. Your prescriber may adjust your dose, switch you to the alternative medication, or recommend stopping treatment depending on severity.
Does the dual mechanism of Mounjaro affect heart health differently than Wegovy?
Mounjaro's dual GIP and GLP-1 mechanism is different from Wegovy's single GLP-1 mechanism, and this may influence cardiovascular effects. However, clinical trial data for both shows cardiac side effects are uncommon. Your prescriber will consider your individual cardiac history when choosing between them.
Are there GLP-1 medications safer for the heart than others?
Both Mounjaro and Wegovy are prescription-only and require clinical assessment. Neither is "safer" universally—suitability depends on your personal health profile. Your GP will assess your cardiac risk factors, blood pressure, heart rate, and medical history to recommend the most appropriate medication for you.
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