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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Mounjaro And GERD: Understanding Acid Reflux Risk
Mounjaro (tirzepatide) is a prescription-only weight management injection that may cause or worsen acid reflux (GERD) in some people. This happens because Mounjaro slows how quickly food leaves your stomach, which can trigger reflux symptoms. If you experience persistent heartburn, regurgitation, or chest discomfort after starting Mounjaro, it's important to discuss this with your GP. Understanding the connection between this medication and GERD can help you manage symptoms effectively and decide whether treatment is right for you.
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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 Your Digestive System
Mounjaro works by activating GIP and GLP-1 receptors, which regulate appetite and support weight loss. However, one side effect of this mechanism is delayed gastric emptying — meaning food stays in your stomach longer than usual. This slower movement can increase pressure in the oesophagus and stomach, potentially triggering acid reflux symptoms.
In clinical trials, indigestion and acid reflux (gastro-oesophageal reflux disease, or GERD) were listed as common side effects affecting up to 1 in 10 people. Symptoms typically include heartburn, regurgitation of food or liquid, difficulty swallowing, or chest pain. The good news is that for many people, these symptoms improve as your body adjusts to the medication, usually within the first few weeks of starting or increasing your dose.
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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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Managing GERD While Taking Mounjaro
If you develop GERD symptoms while taking your Mounjaro KwikPen, try eating smaller, more frequent meals and avoid lying down immediately after eating. Staying upright for at least 2–3 hours after meals can reduce reflux. Avoiding trigger foods like spicy dishes, caffeine, chocolate, and fatty foods may also help.
Your GP or prescriber can suggest over-the-counter antacids or prescription medications like proton pump inhibitors (PPIs) to manage symptoms. However, always inform your prescriber if you're taking other oral medications — Mounjaro may affect how some tablets are absorbed. Never stop taking Mounjaro without medical guidance, even if you experience GERD. Your prescriber can adjust your dose or explore alternative options if symptoms persist.
- 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 everyone taking Mounjaro get GERD?
No. GERD is a common side effect but not inevitable — it affects approximately 1 in 10 people in clinical trials. Many people tolerate Mounjaro without experiencing acid reflux at all. Individual responses vary based on genetics, diet, and existing digestive health.
Can GERD from Mounjaro be permanent?
Most people find that GERD symptoms improve after the first few weeks as their body adjusts. Symptoms are usually temporary and manage-able with lifestyle changes and, if needed, antacid medication. If symptoms persist beyond a few weeks, discuss alternative treatments with your GP.
Should I stop taking Mounjaro if I get GERD?
Do not stop taking Mounjaro without speaking to your prescriber first. Instead, report your symptoms to your GP or the prescriber who issued your Mounjaro UK prescription. They can suggest symptom management strategies, adjust your dose, or discuss whether this medication remains suitable for you.
What's the difference between GERD and normal indigestion on Mounjaro?
Indigestion is mild stomach discomfort, usually after eating. GERD is more persistent acid reflux affecting the oesophagus, causing heartburn, regurgitation, or chest pain. GERD symptoms that last more than a few days warrant a GP consultation to rule out complications.
Can I take antacids while taking Mounjaro?
Yes, over-the-counter antacids (like calcium carbonate) are generally safe with Mounjaro. However, inform your GP of all medications you're taking — Mounjaro may affect absorption of some oral medicines. Your prescriber can recommend the safest option and advise on timing between doses.
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