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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Reducing Mounjaro Dose Side Effects vs Wegovy
If you're experiencing side effects on Mounjaro (tirzepatide), dose reduction is a common and safe option that your prescriber may recommend. Both Mounjaro and Wegovy (semaglutide) can cause nausea, diarrhoea, and stomach discomfort, especially during the first few weeks or when doses are increased. Understanding how these two medications differ in side effect profiles and dose titration schedules can help you and your prescriber decide the best approach for your individual circumstances. This guide compares both medications to help you make informed decisions about weight management treatment.
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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 and Wegovy Differ in Mechanism and Side Effects
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, meaning it activates two natural hormone pathways simultaneously. Wegovy (semaglutide) is a GLP-1 receptor agonist only, activating a single pathway. This dual mechanism in Mounjaro may explain why some users report more pronounced appetite suppression and potentially higher rates of gastrointestinal side effects, particularly during dose escalation.
In clinical trials, Mounjaro showed average weight loss of around 20.9% at the maximum 15 mg dose (SURMOUNT-1 trial), whilst Wegovy achieved approximately 14.9% at 2.4 mg (STEP-1 trial). However, higher efficacy doesn't mean fewer side effects — the dual mechanism can intensify common side effects like nausea and changes in appetite.
- Mounjaro side effects: Very common: nausea, diarrhoea, vomiting, constipation, abdominal pain. Individual experiences vary significantly.
- Wegovy side effects: Very common: nausea, diarrhoea, vomiting, constipation, indigestion. Similar profile to Mounjaro but potentially less severe due to single-mechanism action.
Both are prescription-only medications requiring clinical assessment. Your prescriber may recommend staying on your current dose longer, pausing escalation, or reducing the dose if side effects are problematic.
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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 Side Effects: Dose Reduction and Timing Strategies
If side effects are affecting your quality of life on Mounjaro, dose reduction is a legitimate clinical option and does not mean treatment failure. Many people manage side effects by pausing at a lower dose (e.g., staying on 5 mg or 7.5 mg rather than escalating to 15 mg), which still provides meaningful weight loss whilst tolerability improves.
Common side effect management strategies include: eating smaller, more frequent meals; staying hydrated; avoiding fatty or greasy foods; and allowing 4+ weeks at each dose before escalating. Both Mounjaro and Wegovy require a minimum 4 weeks between dose increases, giving your body time to adapt. If nausea persists beyond the first 4–8 weeks at a stable dose, discuss with your prescriber about pausing escalation or reducing back one dose level. Side effects often improve with time, but individual tolerance varies significantly. Your prescriber can help you find the dose that balances efficacy with tolerability.
- 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.
Should I switch from Mounjaro to Wegovy if I'm having side effects?
Not necessarily. Many side effects improve after the first 4–8 weeks at a stable dose. Before switching, discuss with your prescriber about pausing dose escalation or reducing your Mounjaro dose. A lower dose of Mounjaro may provide better tolerability than switching medications entirely. If side effects persist despite these strategies, your prescriber may recommend Wegovy as an alternative.
Can I stay on a lower Mounjaro dose and still lose weight?
Yes. Clinical trials showed weight loss at all dose levels — 5 mg, 10 mg, 15 mg. Staying on 5 mg or 7.5 mg longer whilst your body adjusts may actually be more sustainable than pushing through severe side effects at higher doses. Individual results vary, and your prescriber can advise what dose best suits your health goals and tolerance.
What's the difference between Mounjaro dose titration and Wegovy dose titration?
Mounjaro starts at 2.5 mg and escalates weekly (5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg). Wegovy starts at 0.25 mg and escalates every 4 weeks (0.5 mg, 1 mg, 1.7 mg, 2.4 mg). Mounjaro escalates faster, which may explain why some users report more intense initial side effects. Slower titration (staying longer at each dose) reduces side effect severity.
How long do Mounjaro side effects typically last?
Most common side effects like nausea and diarrhoea peak during the first 2–4 weeks of starting or increasing a dose, then gradually improve as your body adapts. By week 8 at a stable dose, many people report significant improvement. However, some experience persistent mild symptoms. If side effects don't improve after 8–12 weeks at a stable dose, discuss options with your prescriber.
Is it normal to reduce or pause Mounjaro if side effects are too severe?
Yes, absolutely normal. Your prescriber may recommend staying at your current dose longer, pausing escalation, or temporarily reducing back to a lower dose. There's no "failure" in finding the dose that works for your body. Sustainable treatment means balancing weight loss effectiveness with quality of life and tolerability. Your prescriber will help you find that balance.
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