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 Pros and Cons — Complete UK Overview
Mounjaro (tirzepatide) is a prescription-only weight loss injection licensed in the UK for adults with obesity or overweight with related health conditions. Like all medications, it has both potential benefits and drawbacks worth understanding before considering treatment. This guide covers the realistic advantages and disadvantages to help you make an informed decision alongside your GP or prescriber.
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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.
The Main Benefits of Mounjaro in the UK
Effective weight loss support: In clinical trials (SURMOUNT-1), participants using Mounjaro lost an average of 15–21% of their body weight over 72 weeks, compared to much smaller losses with placebo. Results vary significantly between individuals, but these figures represent meaningful weight loss for many people.
Once-weekly dosing: Unlike some alternatives, Mounjaro is injected only once per week as a pre-filled KwikPen, making it simpler to manage than daily medications. The injection is subcutaneous (under the skin) and can be done at home.
Dual hormone action: Mounjaro activates both GIP and GLP-1 pathways, which may provide greater appetite suppression than single-mechanism alternatives. This dual approach may help reduce food cravings and support feeling fuller after smaller meals.
Health condition improvements: Beyond weight loss, participants in trials showed improvements in blood sugar control, blood pressure, and cardiovascular risk markers, which may reduce risk of type 2 diabetes and heart disease.
- Works alongside lifestyle changes
- Addresses underlying appetite regulation
- May reduce weight-related health risks
Clinically BackedWeight Loss
No appointments. No waiting rooms. Just care — from a UK-regulated online pharmacy.
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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
The Main Drawbacks and Considerations
Gastrointestinal side effects: Nausea, diarrhoea, vomiting, and constipation are very common, especially when starting or increasing doses. These typically improve over time but can be limiting for some people. Stomach pain and indigestion may also occur.
Cost and access barriers: Private Mounjaro costs £129–£320+ per month depending on dose. NHS access is limited to specialist tier 3 weight management services with lengthy waiting lists in most regions. Not everyone meets NHS eligibility criteria.
Ongoing treatment: Weight loss is typically sustained only while taking Mounjaro — stopping the medication often leads to weight regain. This means long-term commitment and expense for sustained results.
Contraindications: Mounjaro is unsuitable for pregnant women, people with certain thyroid or pancreas conditions, and those with personal or family history of medullary thyroid carcinoma. It may interact with oral contraceptives.
- Requires prescription and clinical assessment
- May not suit everyone's medical profile
- Individual tolerance varies widely
- 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 available on the NHS in the UK?
NHS access to Mounjaro (tirzepatide) is available through specialist tier 3 weight management services, following NICE approval. However, availability varies significantly by region and waiting times can be lengthy. Most people access it privately through UK-licensed prescribers and GPhC-registered pharmacies after online clinical assessment. Your GP can advise on NHS eligibility and local referral pathways.
How does Mounjaro compare to Wegovy for weight loss?
Both are prescription-only weight loss injections licensed in the UK. Mounjaro uses dual GIP and GLP-1 mechanisms, while Wegovy (semaglutide) activates GLP-1 only. Clinical trials show slightly higher average weight loss with Mounjaro (15–21% vs approximately 15% with Wegovy), but individual results vary widely. The best choice depends on your medical history, tolerance, and prescriber assessment.
What happens to weight when you stop taking Mounjaro?
Weight loss achieved with Mounjaro is typically maintained only while taking the medication. Most people experience gradual weight regain after stopping, especially without sustained lifestyle changes. This means Mounjaro is usually considered a long-term treatment rather than a short-term fix. Your prescriber will discuss sustainability and long-term plans.
Are the side effects of Mounjaro permanent?
Most Mounjaro side effects (nausea, diarrhoea, constipation) are temporary and tend to improve within weeks as your body adjusts, particularly when doses are increased gradually. However, some people experience persistent gastrointestinal effects. Rare serious side effects like pancreatitis require immediate medical attention. Always report concerning symptoms to your prescriber.
Can I use MyWeightCheck tools to track progress on Mounjaro?
Yes — use our free BMI calculator to track your BMI changes week by week, our weight converter to log weight in your preferred units (stone, kg, or lbs), and our GLP-1 weight loss calculator to understand potential outcomes at different doses. Our progress tracker helps you visualise your weight loss journey and maintain motivation throughout treatment.
Ready to take control of your weight loss journey?
Start with a free BMI check, explore your GLP-1 options, or begin tracking your progress today. No sign-up. No cost. Just results.