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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Acid Reflux on Mounjaro — What You Need to Know
Acid reflux (gastro-oesophageal reflux disease, or GORD) is a common side effect reported by people taking Mounjaro (tirzepatide) in the UK. This happens because Mounjaro slows how quickly food leaves your stomach, which can increase stomach acid exposure to the oesophagus. While this effect typically reduces over time as your body adjusts, understanding how to manage it is important. This guide explains what happens, when to seek help from your GP, and practical steps you can take whilst taking this prescription weight management injection.
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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 is a dual GIP and GLP-1 receptor agonist — it activates two natural hormone pathways involved in appetite and digestion. One key effect is slowing gastric emptying, which means food moves more slowly from your stomach into your small intestine. This is intentional and helps create the sensation of fullness that supports weight loss.
However, this delayed stomach emptying can allow stomach acid to remain in contact with the oesophageal lining for longer, causing heartburn or acid reflux symptoms. NHS data shows this is among the most frequently reported side effects of tirzepatide, particularly in the first weeks of treatment. The good news is that this effect often diminishes as your body adapts — many people find symptoms improve significantly by weeks 8–12 of treatment, even if they continue the same dose. If you're prescribed Mounjaro through NHS specialist weight management services or privately following a clinical assessment, your prescriber should have discussed digestive side effects and monitoring with you.
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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 Acid Reflux While Taking Mounjaro
Practical management strategies can help reduce acid reflux symptoms whilst taking Mounjaro. Eat smaller, more frequent meals rather than large meals; avoid trigger foods like spicy, fatty, or acidic foods; do not lie down immediately after eating; and stay upright for at least 2–3 hours after meals. Some people find relief from over-the-counter antacids (such as calcium carbonate or magnesium hydroxide) or H2 blockers (like ranitidine alternatives). However, always check with your GP or pharmacist before starting any new medication, especially if you're taking other prescribed medicines — Mounjaro can affect how oral medications are absorbed.
If acid reflux is significantly affecting your quality of life, contact your GP. They may recommend a proton pump inhibitor (PPI) like omeprazole, which reduces stomach acid production and is commonly prescribed alongside weight loss medications in the UK. Your GP can also assess whether continuing Mounjaro is right for you or whether a dose adjustment might help.
- 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 acid reflux a serious side effect of Mounjaro?
Acid reflux is common but usually manageable. It's not dangerous in itself, but persistent severe reflux can damage the oesophagus over time. Contact your GP if symptoms are severe, persistent, or affecting your daily life. Most people find symptoms improve as their body adjusts to the medication within a few weeks.
Will acid reflux stop if I continue taking Mounjaro?
For many people, yes. The gastric emptying effect of tirzepatide often reduces after the initial weeks, and acid reflux symptoms typically improve by weeks 8–12 even at the same dose. However, some people experience persistent reflux, in which case your GP can recommend management options or assess whether the medication remains appropriate for you.
Can I take antacids or PPI medication with Mounjaro?
Yes, antacids and proton pump inhibitors are commonly used alongside Mounjaro. However, PPIs may reduce absorption of some oral medications. Always inform your GP or pharmacist that you're taking Mounjaro before starting any new medication, including over-the-counter options. They can advise on the best approach for your individual situation.
What's the difference between Mounjaro and Wegovy regarding acid reflux?
Both Mounjaro (tirzepatide) and Wegovy (semaglutide) can cause acid reflux as they both slow gastric emptying. Mounjaro is a dual GIP and GLP-1 agonist, whilst Wegovy is a GLP-1 agonist only. Clinical trial data suggests Mounjaro may support greater weight loss, but individual side effect experiences vary. Your GP can help you decide which is most appropriate if you're choosing between them.
Should I stop taking Mounjaro if I develop acid reflux?
Do not stop taking Mounjaro without speaking to your prescriber first. Instead, contact your GP to discuss symptoms and explore management options. Many people successfully manage acid reflux whilst continuing Mounjaro. Your prescriber can advise whether continuing, adjusting the dose, or switching to an alternative medication is best for you.
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