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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How Mounjaro and Wegovy Affect Heart Rate
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) are prescription-only weight management injections used in the UK, and changes to heart rate have been reported by some users. Understanding how these medications work and what clinical evidence shows about heart rate effects can help you make an informed decision with your GP. This guide compares the two medications directly, using data from UK-licensed trials and real-world experience.
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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 Evidence on Heart Rate and GLP-1 Medications
Heart rate changes are not listed as common side effects in either the SURMOUNT-1 trial (Mounjaro) or STEP-1 trial (Wegovy) data. However, both medications can cause dizziness and fatigue in some users, which may be associated with physiological changes including heart rate variations.
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two hormone pathways simultaneously. Wegovy (semaglutide) activates only the GLP-1 pathway. This mechanistic difference could theoretically affect cardiovascular responses, though direct clinical comparisons are limited.
- Mounjaro: Dizziness reported in common side effects; heart palpitations rare but possible
- Wegovy: Dizziness and fatigue documented; heart rate monitoring may be warranted if you have cardiac risk factors
- Both: Any significant heart rate changes should be reported to your GP immediately
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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.
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Which Medication Might Be Suitable for You?
Choosing between Mounjaro and Wegovy depends on your individual health profile, not just heart rate concerns. Both are prescription-only medications requiring a full clinical assessment before prescription. Your GP or prescriber will review your cardiac history, current medications, blood pressure, and overall health to determine which is safer for you.
If you have a history of heart arrhythmias, high blood pressure, or other cardiovascular conditions, inform your prescriber immediately. They may recommend additional monitoring, dose adjustment, or a different medication entirely. Use our free GLP-1 weight loss calculator to explore potential outcomes, and discuss any heart rate concerns during your clinical assessment.
- 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 heart rate changes?
Heart rate changes are not a common side effect in clinical trials, but dizziness and fatigue can occur, which may affect how you feel physically. If you notice persistent heart rate changes after starting Mounjaro, contact your GP immediately. Any medication affecting appetite and energy can have secondary effects on heart function in some individuals.
Is Wegovy safer for heart rate than Mounjaro?
Both medications have similar safety profiles regarding heart function. Neither has significantly higher rates of heart rate issues in clinical trials. The choice between them depends on your individual health, prescriber recommendation, and response to treatment. Only a licensed prescriber can assess which is safer for you personally.
Should I have my heart rate monitored on these medications?
If you have existing heart conditions, high blood pressure, or take cardiac medications, your GP should monitor you. Standard monitoring includes blood pressure checks and heart rate assessment at each dose increase. Report any chest pain, severe palpitations, or fainting immediately—these are not expected side effects.
What heart rate changes are considered normal on GLP-1 injections?
Minor variations in resting heart rate (a few beats per minute) can occur as your body adjusts to any medication. However, significant increases, irregular heartbeats, or accompanied chest discomfort are not normal and require urgent GP assessment. Most users experience no heart rate changes at all.
Can I take Mounjaro or Wegovy if I have a heart condition?
Having a heart condition doesn't automatically exclude you, but your prescriber must know about it. Some cardiac conditions may require closer monitoring or dose adjustments. Others may mean these medications aren't suitable. Your full medical history must be assessed before prescription—always disclose all health conditions and medications.
Ready to take control of your weight loss journey?
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