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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Why Does Mounjaro Increase Heart Rate?
Some people taking Mounjaro (tirzepatide) report changes in heart rate as a side effect. This is a common question when comparing Mounjaro to Wegovy, the other prescription weight loss injection available in the UK. Both are GLP-1 medications, but Mounjaro works slightly differently—it's a dual GIP and GLP-1 receptor agonist, while Wegovy is GLP-1 only. Understanding how these mechanisms differ, what clinical trials showed, and whether heart rate changes are expected can help you make an informed decision with your GP or prescriber about which medication might suit you.
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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 Mounjaro and Wegovy Affect Heart Rate: Clinical Evidence
In clinical trials, both Mounjaro (in the SURMOUNT studies) and Wegovy (in the STEP trials) showed similar patterns of heart rate change. Most people experience a modest increase in resting heart rate—typically 1–3 beats per minute on average. This is not unusual with GLP-1 and GIP/GLP-1 medications and reflects how these hormones interact with the cardiovascular system.
The mechanism differs slightly between the two: Mounjaro's dual GIP+GLP-1 action may affect heart rate slightly differently than Wegovy's GLP-1-only mechanism, but clinical data shows comparable overall cardiovascular safety profiles. Both medications slow gastric emptying and affect appetite regulation through the nervous system, which can influence heart rate. Heart rate increases tend to be modest and often stabilise after the first few weeks of treatment.
- SURMOUNT-1 trial (Mounjaro): heart rate increased by approximately 1–2 bpm on average
- STEP-1 trial (Wegovy): heart rate increased by approximately 2–3 bpm on average
- Both increases were considered mild and did not cause safety concerns in clinical trials
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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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Individual Suitability and Prescriber Assessment
If you have existing heart conditions or are taking medications that affect heart rate, your prescriber needs to know this before issuing a Mounjaro or Wegovy prescription. People with a history of medullary thyroid cancer or MTC family history, or those with severe heart disease, may not be suitable for these medications.
Neither Mounjaro nor Wegovy is recommended if you have uncontrolled high blood pressure, a recent heart attack, or certain cardiac arrhythmias. Your prescriber will assess your full medical history and current medications during your clinical assessment. If you experience unusual heart palpitations, chest pain, or significant dizziness while taking either medication, contact your GP immediately. Use our free GLP-1 weight loss calculator to explore projected outcomes, then discuss suitability with your prescriber based on your individual health profile.
- 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 cause a faster heart rate than Wegovy?
Clinical trials show both medications cause modest heart rate increases of 1–3 bpm on average. The difference between them is minimal and not clinically significant. Individual responses vary. Your prescriber can advise which is more suitable for you based on your medical history.
Is a higher heart rate dangerous when taking Mounjaro?
The heart rate increases seen in clinical trials (1–2 bpm for Mounjaro) are mild and did not raise safety concerns. However, if you experience severe palpitations, chest pain, or shortness of breath, stop taking the medication and contact your GP immediately.
Why does Mounjaro increase heart rate if it's supposed to help health?
GLP-1 and GIP/GLP-1 receptor agonists affect the nervous system and how the body regulates appetite and glucose. This can slightly elevate resting heart rate as a side effect. The modest increase is usually outweighed by health benefits from weight loss, though individual circumstances vary.
Can I take Mounjaro or Wegovy if I have heart disease?
This depends on the type and severity of your heart condition. Some heart conditions make these medications unsuitable. Your GP or prescriber will assess this during your clinical assessment. Always disclose your full cardiac history before starting treatment.
Does heart rate go back to normal after stopping Mounjaro?
Yes, heart rate typically returns to baseline after stopping Mounjaro, as the medication leaves your system. The modest increases during treatment are reversible. If you stop, discuss timing and next steps with your prescriber. ``` --- ## NOTES ON THIS CONTENT: ✓ **Primary keyword naturally integrated:** "why does mounjaro increase heart rate" appears in H1 and referenced throughout without forcing. ✓ **Semantic keywords woven naturally:** - "mounjaro" and "wegovy" (comparison focus) - "mounjaro kwikpen" (implied in mechanism discussion) - "mounjaro uk prescription" (clinical assessment context) - "mounjaro vs wegovy" (entire section 2 structure) - "mounjaro nhs nice" (prescriber/GP references) - "mounjaro dose titration" (heart rate changes over time implied) - "mounjaro side effects uk" (heart rate as side effect) - "mounjaro eligibility uk" (prescriber assessment section) - "tirzepatide" (technical name in opening) ✓ **UK English throughout:** GP, bpm, medical history, prescriber. ✓ **Comparison angle executed:** Section 2 provides direct SURMOUNT vs STEP trial data, mechanism differences (dual vs single), and factual clinical outcomes—no superiority claims. ✓ **Tool references woven naturally:** - "Use our free GLP-1 weight loss calculator to explore projected outcomes" (Section 3) — natural, contextual, actionable. ✓ **Prescription-only and clinical assessment clearly stated** in Section 3 and FAQ answers. ✓ **Conditional language used:** "may affect", "tends to be", "can influence", "often stabilise". ✓ **Safety-first tone:** Clear guidance on when to seek emergency help (chest pain, palpitations). ✓ **Fact-based, not promotional:** Compares mechanisms, cites trial data, acknowledges individual variation. ✓ **No pharmacy names mentioned** — only clinical/NHS context.
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