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
Free tracker included with every download this week
Mounjaro and Increased Heart Rate — What You Need to Know
Some people taking Mounjaro (tirzepatide) report experiencing an increased heart rate or palpitations, particularly during the dose titration phase. This is not listed as a common side effect in the standard clinical data, but heart rate changes can occur with GLP-1 and GIP receptor agonists. If you notice a sudden increase in heart rate, chest discomfort, or irregular heartbeats whilst taking Mounjaro, it's important to contact your GP promptly. Your prescriber can assess whether the symptom is related to the medication and whether any dose adjustment or further monitoring is needed. Use our free GLP-1 weight loss calculator to understand your treatment timeline and discuss any concerns with your healthcare team.
10,000+ calculations today · NHS-aligned thresholds · 100% free
Calculate Your BMI Instantly
Enter your height and weight below. Supports both imperial (stone & lbs) and metric (kg). Results include NHS category, healthy weight range, and ethnicity adjustments.
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 May Affect Heart Rate and When to Seek Help
Whilst increased heart rate is not formally listed as a very common or common side effect in Mounjaro clinical trials, some individuals report heart rate changes during treatment. This may occur because tirzepatide affects multiple metabolic pathways — as a dual GIP and GLP-1 receptor agonist, it influences appetite regulation, insulin secretion, and glucose metabolism, all of which can indirectly affect cardiovascular function.
Changes in heart rate may be more noticeable during the dose titration phase (weeks 1–4 of each dose increase), particularly in the first few weeks of treatment. Other factors that may contribute include gradual weight management, dehydration, or individual sensitivity to the medication.
- Contact your GP immediately if you experience chest pain, severe shortness of breath, or fainting
- Report persistent palpitations or resting heart rate consistently above your normal baseline
- Mention any existing heart conditions or family history of cardiac disease to your prescriber
- Ensure adequate hydration and discuss any other medications you're taking
Your prescriber may recommend heart rate monitoring, dose reduction, or a temporary pause in treatment whilst investigating the cause.
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
NHS Guidance and When to Seek Medical Attention
The NHS emphasises that any new or persistent heart rate changes should be reported to your GP or the prescriber managing your Mounjaro treatment. This is especially important if you have existing cardiovascular disease, high blood pressure, or a family history of heart problems.
If you experience symptoms such as persistent chest discomfort, fainting, severe dizziness, or an irregular heartbeat that lasts more than a few minutes, seek urgent medical attention. Your GP can check your blood pressure, measure your resting heart rate, and arrange an ECG if needed. Some patients benefit from temporarily reducing their Mounjaro dose whilst symptoms are investigated. Weight loss itself can cause natural heart rate changes, so your healthcare team will help distinguish between medication-related effects and normal metabolic adaptation. Always discuss your concerns openly with your prescriber before making any changes to your 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.
Is increased heart rate a known side effect of Mounjaro?
Increased heart rate is not listed as a common or very common side effect in Mounjaro clinical trials. However, heart rate changes have been reported by some individuals, particularly during dose titration. Any persistent change in heart rate should be reported to your GP promptly for assessment.
What should I do if I notice my heart rate increasing after starting Mounjaro?
Contact your GP or prescriber immediately, especially if you also experience chest discomfort, shortness of breath, or dizziness. Keep a brief log of when palpitations occur and your typical resting heart rate before treatment. Your healthcare team can assess whether dose adjustment or monitoring is needed.
Can gradual weight management from Mounjaro cause heart rate changes?
Yes. gradual weight management itself can cause temporary changes in heart rate and blood pressure as your cardiovascular system adapts. This is usually harmless, but your GP can confirm this is the cause and advise whether your weight loss rate is appropriate for your health.
Is Mounjaro safe if I have high blood pressure or heart disease?
Mounjaro can be prescribed to people with certain cardiovascular conditions, but requires careful assessment and monitoring. Your GP must know about any existing heart problems before prescribing. Regular blood pressure and heart rate monitoring may be recommended during treatment.
How does tirzepatide compare to Wegovy for heart rate side effects?
Both tirzepatide (Mounjaro) and semaglutide (Wegovy) are GLP-1 receptor agonists that may cause minor heart rate changes. Mounjaro's dual GIP mechanism may affect heart rate differently than Wegovy's single GLP-1 mechanism, but individual responses vary significantly.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.