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 experiencing an increased heart rate as a side effect. This happens because GIP and GLP-1 receptor agonists can affect heart rate regulation, particularly during the dose titration phase when your body is adjusting to the medication. While not everyone experiences this, understanding why it occurs and when to seek medical advice is important. Changes in heart rate are usually temporary, but any persistent or concerning symptoms should be discussed with your GP.
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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 Affects Heart Rate and Blood Pressure
Mounjaro works by activating GIP and GLP-1 hormone pathways, which influence how your body regulates appetite, blood sugar, and cardiovascular function. During dose titration — the gradual increase from the starting 2.5 mg dose up to the maintenance dose — your cardiovascular system is adapting to these new signals. This adjustment period can sometimes cause a temporary increase in heart rate or blood pressure changes.
Clinical data shows that heart rate changes are more common in the first few weeks of treatment or when increasing doses. Your heart rate may increase by 5–10 beats per minute during this adjustment phase. Most people find their heart rate stabilises after several weeks on a stable dose. However, if you have a history of heart problems, high blood pressure, or take medications that affect heart rate, inform your prescriber before starting Mounjaro, as individual monitoring may be needed.
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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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When to Contact Your GP About Heart Rate Changes
Contact your GP immediately if you experience persistent rapid heartbeat lasting more than a few minutes, chest pain or pressure, shortness of breath out of proportion to activity, or dizziness and fainting. These could indicate a more serious cardiovascular issue requiring urgent assessment. For milder heart rate increases that settle within hours, keep a note of when they occur and mention this at your next review appointment.
Your GP can check your blood pressure and heart rate during routine follow-ups and assess whether Mounjaro is right for you. If heart rate increases become problematic, your prescriber may slow your dose titration schedule or recommend an alternative weight management approach. Always report any new or worsening symptoms — do not stop taking Mounjaro without medical guidance.
- 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 common side effect of Mounjaro?
Heart rate changes are reported but not listed as "very common" in clinical data. Most people tolerate Mounjaro well. If you do experience changes, they are usually temporary during dose adjustment. Monitor your symptoms and discuss any concerns with your GP.
Why does Mounjaro affect heart rate differently than Wegovy?
Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is GLP-1 only. Mounjaro's dual mechanism may affect cardiovascular regulation slightly differently, though both medications can influence heart rate in some individuals. Individual responses vary considerably.
How long does increased heart rate last when starting Mounjaro?
Heart rate elevations typically settle within the first few weeks as your body adapts to the medication. If changes persist beyond 4–6 weeks on a stable dose, contact your GP. Slowing the dose titration schedule may help if heart rate increases are problematic.
Can I take Mounjaro if I have existing heart problems?
Mounjaro can be used by people with cardiovascular conditions, but requires careful assessment and monitoring. Inform your prescriber about any heart history, high blood pressure, or relevant medications. Your GP or specialist will decide if Mounjaro is appropriate and arrange appropriate monitoring.
What's the difference between Mounjaro and tirzepatide?
Mounjaro is the brand name for tirzepatide. They are the same medication — tirzepatide is the active ingredient. Both terms refer to the same once-weekly GIP and GLP-1 receptor agonist injection used for weight management in the UK.
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