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 Acid Reflux vs Wegovy — What's the Difference?
Acid reflux and indigestion are common side effects when starting GLP-1 or dual GIP/GLP-1 weight loss medications like Mounjaro and Wegovy. Both medications can affect digestion, but they work differently and individual responses vary. This guide compares the two based on clinical trial data and UK prescribing context, helping you understand how your GP or prescriber decides which medication might be more suitable for you. Always discuss any concerns about acid reflux with your healthcare provider — they can adjust doses or suggest management strategies alongside medication.
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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.
Clinical Data on Acid Reflux: SURMOUNT vs STEP Trials
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist — this dual mechanism means it affects digestion in two ways, which may explain why indigestion and acid reflux are reported in clinical trials. In the SURMOUNT-1 trial, indigestion (dyspepsia) occurred in approximately 13–17% of participants across doses, and acid reflux (GORD) in around 6–10%. These side effects were often mild to moderate and typically improved over time as the body adjusted to the medication.
Wegovy (semaglutide) is a GLP-1-only receptor agonist. In the STEP-1 clinical trial, indigestion occurred in approximately 8–12% of participants, and acid reflux was reported in around 4–7%. The lower rate of gastrointestinal side effects with Wegovy may reflect its single-mechanism action — it activates only the GLP-1 pathway, not the additional GIP pathway that Mounjaro engages.
Important context: Both medications slow gastric emptying (how quickly food leaves the stomach), which can trigger reflux symptoms in some people. Individual responses vary significantly — some people experience no reflux at all, whilst others find it troublesome even at low doses.
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If your BMI suggests you're overweight or obese, explore our GLP-1 calculators to project potential weight loss on Mounjaro or Wegovy.
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How Your GP Decides Between Them — Individual Suitability
Your prescriber will not choose between Mounjaro and Wegovy based on acid reflux risk alone. Instead, they assess your overall health profile: weight, BMI, any existing digestive conditions (like gastroparesis or IBS), concurrent medications, and previous medication responses. Use our free GLP-1 weight loss calculator to explore potential outcomes with either medication — this can help you ask informed questions at your consultation.
If you have a history of acid reflux or GORD, inform your prescriber before starting either medication. Acid reflux can usually be managed with lifestyle adjustments (eating smaller, slower meals; avoiding trigger foods; staying upright after eating) or additional medications like antacids or proton pump inhibitors (PPIs). Starting at a lower dose and titrating slowly — as both medications require — may also reduce reflux symptoms. Your GP can monitor your response and adjust accordingly.
- 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 Mounjaro more likely to cause acid reflux than Wegovy?
Clinical trial data suggests Mounjaro shows slightly higher rates of indigestion and acid reflux than Wegovy (approximately 13–17% vs 8–12% for indigestion). However, individual responses vary widely — some people tolerate Mounjaro well with no reflux, whilst others may experience reflux on Wegovy. Your personal medical history, dose, and how quickly you escalate doses all influence risk.
Can acid reflux be managed whilst taking Mounjaro or Wegovy?
Yes, in most cases. Lifestyle changes (smaller meals, slower eating, staying upright after eating, avoiding trigger foods) help significantly. Your GP can also prescribe antacids or proton pump inhibitors (PPIs) alongside the injection to manage reflux. Starting at a low dose and titrating slowly also minimises digestive side effects.
How do Mounjaro and Wegovy differ in how they work?
Mounjaro is a dual GIP and GLP-1 receptor agonist — it activates two hormone pathways. Wegovy is a GLP-1-only agonist. The dual mechanism in Mounjaro may offer stronger weight loss results in some trials (average ~20% vs ~15% body weight), but also carries slightly higher rates of gastrointestinal side effects including reflux.
Will my GP prescribe one over the other if I have GORD?
If you have pre-existing acid reflux or GORD, your prescriber will take this into account. They may still prescribe either medication, but may start at a lower dose, escalate more slowly, or recommend additional acid-suppressing medication alongside the injection. Always disclose your full medical history during your clinical assessment.
How long does acid reflux last when starting Mounjaro or Wegovy?
Most gastrointestinal side effects, including acid reflux, peak in the first few weeks then gradually improve as your body adjusts. Many people find reflux symptoms reduce or resolve by 8–12 weeks. If reflux persists beyond the adjustment period, your prescriber can adjust your dose or medication.
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