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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Does Mounjaro Cause Heart Palpitations?
Heart palpitations are not listed as a common side effect of Mounjaro (tirzepatide) in clinical trials, though some patients report experiencing them. If you notice an irregular heartbeat, chest fluttering, or unusual heart sensations after starting this prescription weight management medication, it's important to contact your GP for assessment. This guide explains what heart palpitations are, how they relate to Mounjaro, and what steps you should take. Always discuss any new symptoms with your healthcare provider before adjusting your treatment.
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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.
What Are Heart Palpitations and Why Do They Happen?
Heart palpitations are the sensation of your heartbeat becoming noticeable — you may feel a fluttering, racing, skipping, or pounding in your chest. Most palpitations are harmless and short-lived, but they can be concerning. Several factors may trigger palpitations on weight management medications:
- gradual weight management: Losing weight quickly can affect your heart's workload and blood pressure, potentially triggering palpitations
- Electrolyte changes: Nausea and digestive side effects can deplete electrolytes (sodium, potassium), which regulate heart rhythm
- Anxiety or stress: Starting a new medication or worrying about health can increase heart rate
- Dehydration: Common during weight loss if fluid intake is insufficient
- Caffeine sensitivity: Some people become more sensitive to caffeine when taking GIP/GLP-1 agonists
- Underlying factors: Pre-existing heart conditions, thyroid issues, or other medications may be involved
In clinical trials of Mounjaro, heart palpitations were not reported as a frequent side effect, though individual experiences vary. If you develop palpitations, this does not automatically mean you must stop the medication — it means your GP needs to evaluate what's causing them.
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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 Should You Contact Your GP?
Contact your GP immediately if you experience:
- Chest pain or pressure alongside palpitations
- Severe shortness of breath or dizziness
- Fainting or loss of consciousness
- Persistent palpitations lasting more than a few minutes
- A heartbeat that feels dangerously fast (over 120 bpm at rest)
- Signs of a panic attack that won't resolve
Call 999 or go to A&E if symptoms are severe. For mild, occasional palpitations, contact your GP within a few days to discuss when you started experiencing them, how long they last, and whether adjusting your Mounjaro dose or other factors might help. Your prescriber may recommend heart checks or adjustments to your tirzepatide titration schedule.
- 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.
Are heart palpitations a known side effect of Mounjaro?
Heart palpitations are not listed as a common or very common side effect of Mounjaro in clinical trials. However, some patients report experiencing them. The SURMOUNT trials did not report palpitations as a frequent adverse event, but individual experiences vary. Always report any unusual heart sensations to your GP.
Can gradual weight management from Mounjaro cause palpitations?
Yes, gradual weight management can sometimes trigger heart palpitations because your heart's workload changes as your body weight decreases. Losing weight too quickly can affect blood pressure and electrolyte balance. The NHS recommends losing no more than 0.5–1 kg per week for sustainable results. Slower, steady weight loss is easier on your heart.
What should I do if I get heart palpitations while taking Mounjaro?
Contact your GP. Describe when the palpitations started (before or after starting Mounjaro), how long they last, and any other symptoms. Your GP may examine you, check your heart rate, or arrange an ECG. Do not stop taking Mounjaro without medical advice — your GP may adjust your dose, investigate other causes, or recommend heart monitoring.
Could dehydration or electrolytes explain palpitations on Mounjaro?
Yes. Mounjaro commonly causes nausea, vomiting, and diarrhoea, which can deplete fluids and electrolytes like potassium. Low electrolytes can cause heart rhythm problems. Ensure you're drinking enough water and eating nutrient-rich foods. Your GP may check your electrolyte levels with a blood test if palpitations persist.
Is Mounjaro safe if I have a history of heart problems?
Mounjaro requires a clinical assessment before prescription. If you have any history of heart disease, high blood pressure, or irregular heartbeat, tell your prescriber. They will evaluate whether Mounjaro is safe for you or whether heart monitoring is needed. Your GP can also provide personalised guidance based on your medical history. ```
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