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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Is Mounjaro Dangerous? What You Need to Know
Mounjaro (tirzepatide) is a prescription-only weight loss injection licensed in the UK, but like all medications, it carries potential risks and side effects. The key question isn't whether Mounjaro is inherently "dangerous"—it's understanding whether the benefits outweigh the risks for your individual circumstances. This guide explores the safety profile, common side effects, serious risks to watch for, and the real costs of accessing Mounjaro in the UK through both NHS and private routes. Use our free BMI calculator to understand your starting point before considering any weight loss 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.
Mounjaro Safety Profile and Side Effects in the UK
Mounjaro's safety has been evaluated in clinical trials, most notably the SURMOUNT-1 study, which tracked over 2,000 participants. The majority of side effects are gastrointestinal—nausea, diarrhoea, vomiting, and constipation are very common, affecting more than 1 in 10 users, particularly during dose escalation. These typically improve as your body adjusts.
More serious but rare side effects include pancreatitis (severe stomach pain radiating to the back), gallbladder problems, and changes in vision, particularly if you have a history of diabetic retinopathy. Mounjaro is subject to additional MHRA monitoring (Black Triangle ▼ status), meaning the regulator is actively tracking safety data. Tirzepatide cannot be used if you're pregnant, breastfeeding, or under 18. If you have a personal or family history of medullary thyroid cancer, Mounjaro is contraindicated. Always inform your prescriber of all existing health conditions and medications before starting.
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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.
Mounjaro Cost and Access in the UK
NHS access: Mounjaro is approved by NICE for NHS use within specialist tier 3/4 weight management services, but access is heavily dependent on your region and local commissioning. Waiting lists can be very long (sometimes 12+ months), and not all areas currently prescribe it. You'll need a GP referral to a specialist weight management service.
Private access: Through private online prescribing, a single dose (one KwikPen, 4 weeks) ranges from £129–£320 depending on strength and provider. A full dose escalation course (starting at 2.5mg through to 15mg maintenance) typically costs £1,500–£3,000 over several months. Costs vary by provider. Online consultations are usually £20–£50. Always use a GPhC-registered pharmacy and ensure prescribers are UK-licensed.
- 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 safer than Wegovy?
Both are GLP-1-based medications with similar side effect profiles. Mounjaro uses a dual GIP+GLP-1 mechanism (potentially more effective for weight loss), while Wegovy is GLP-1 only. Clinical trial data shows slightly higher average weight loss with Mounjaro (20.9% vs 14.9%), but both carry comparable risks. Neither is "safer"—safety depends on individual health factors and medical supervision.
What happens if I stop taking Mounjaro?
Weight typically returns gradually over months as appetite regulation returns to baseline. There's no acute danger from stopping, but you may experience rebound weight gain. Some people transition to lifestyle management alone; others continue with alternative treatments. Always discuss stopping plans with your prescriber rather than stopping abruptly.
Can I use Mounjaro if I have type 2 diabetes?
Yes, Mounjaro can be used for weight management in people with type 2 diabetes. However, if you're already taking diabetes medications like insulin or sulphonylureas, your doses may need adjustment because Mounjaro affects blood sugar regulation. Your prescriber will monitor and adjust medications accordingly.
How do I know if I'm eligible for Mounjaro on the NHS?
NHS eligibility typically requires a BMI of 30 or above, or 27–29.9 with weight-related health conditions (type 2 diabetes, high blood pressure, cardiovascular disease, sleep apnoea). Lower thresholds (BMI 27.5+) apply if you're of South Asian, Chinese, Black African, or Black Caribbean heritage. Ask your GP about referral to a specialist weight management service in your area.
What's the difference between Mounjaro and Ozempic?
Both contain semaglutide from Novo Nordisk, but Ozempic is approved for type 2 diabetes (doses up to 2mg). Mounjaro (tirzepatide) is approved specifically for weight management (doses up to 15mg) and uses a different dual mechanism. Ozempic is not licensed for weight loss in the UK—using it off-label for weight loss is not recommended by NICE or the MHRA.
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.