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
Free tracker included with every download this week
Is Mounjaro Safe for Long-Term Use?
Mounjaro (tirzepatide) is a prescription-only weight management injection that has shown safety and efficacy in clinical trials, but like all medications, long-term use requires careful monitoring. The evidence suggests it may be safe when prescribed appropriately and used under medical supervision, though ongoing research continues to build the safety profile. Your GP or prescriber will assess whether Mounjaro is suitable for you based on your individual health circumstances.
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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.
Clinical Trial Data and What We Know
Mounjaro has been studied in the SURMOUNT clinical trials, which tracked participants for up to 72 weeks. The published data shows that tirzepatide was generally well-tolerated at all doses (2.5 mg to 15 mg once weekly). However, it's important to note that 72 weeks is relatively short-term in medication terms — longer-term safety data (beyond 2 years) is still being collected. The most common side effects were gastrointestinal, particularly nausea, diarrhoea, and constipation, which typically improved over time as the body adjusted to the medication. Serious adverse events were rare in trials, though pancreatitis, gallbladder problems, and vision changes have been reported. Because Mounjaro carries a Black Triangle ▼ symbol in the UK, it remains under additional MHRA monitoring, meaning any new safety concerns are tracked closely and reported regularly. Your prescriber will discuss these risks with you during your clinical assessment.
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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.
Free Weight Loss Tools & Guides
Everything you need to understand your weight, explore medication options, and track your progress — completely free.
Ongoing Monitoring and Long-Term Safety Considerations
If prescribed Mounjaro, you'll need regular check-ins with your prescriber to monitor blood sugar levels, pancreatic markers, and overall health. The UK's NICE guidance recommends that patients remain under specialist weight management service oversight while on treatment. Long-term use (beyond 2 years) is still being studied — some patients may continue indefinitely while others may stop after reaching their goals. There is no established maximum duration of treatment yet. If you stop Mounjaro, weight regain is common without sustained lifestyle changes. Before starting, your prescriber will review your medical history, current medications (particularly oral contraceptives and diabetes drugs), and any personal or family history of thyroid cancer or pancreatitis. You can use our free GLP-1 weight loss calculator to explore projected outcomes, but this should never replace a conversation with your prescriber about safety and suitability.
- 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.
Has Mounjaro been used long-term in the UK?
Mounjaro was approved for UK use in 2023, so real-world long-term data is still limited. Clinical trials followed participants for up to 72 weeks. Longer-term safety data (2+ years) is being collected through ongoing studies and post-market surveillance. Your prescriber can discuss the latest evidence available.
What long-term side effects should I be concerned about?
The most common long-term concerns are persistent gastrointestinal symptoms (nausea, constipation) and potential gallbladder issues. Pancreatitis, though rare, has been reported. The MHRA's Black Triangle status means new safety signals are monitored closely. Always report any new or worsening symptoms to your prescriber immediately.
Can I take Mounjaro indefinitely?
There is no established maximum treatment duration yet. Some patients may continue long-term while others stop after reaching their goals. Your prescriber will assess whether continued use is appropriate for you based on your health, weight management goals, and any new safety information. Regular reviews are essential.
What monitoring will I need while on Mounjaro long-term?
You'll need regular check-ins with your prescriber to monitor blood sugar, pancreatic markers, and general health. If prescribed through the NHS, you'll remain under specialist weight management service oversight. Blood tests and clinical reviews are typically done every few months initially, then annually if stable.
What happens if I stop taking Mounjaro after long-term use?
Weight regain is common without sustained lifestyle changes. There are no withdrawal effects, but gradual weight return typically occurs over weeks to months. Your prescriber can discuss a stopping plan and strategies to maintain any weight loss achieved through diet and exercise.
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.