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
Does Mounjaro Stop Working Over Time?
Some people taking Mounjaro (tirzepatide) experience weight loss plateaus or feel that the injection becomes less effective over time. This is a real concern for many adults considering or using this prescription-only weight management medicine in the UK. Understanding why this happens, what you can do about it, and how to access Mounjaro — whether through NHS specialist services or private prescription — helps you make informed decisions about your weight management journey. Using our free GLP-1 weight loss calculator can help you set realistic expectations for your treatment.
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Calculate Your BMI Instantly
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.
Why Weight Loss Plateaus Happen with Mounjaro
Weight loss plateaus on Mounjaro are common and don't necessarily mean the medication has "stopped working." Several factors explain why:
- Dose tolerance: Your body may adapt to your current dose over weeks or months. Your GP or prescriber may increase your dose to restore effectiveness — the standard Mounjaro dose titration schedule includes doses from 2.5 mg up to 15 mg weekly.
- Lifestyle factors: If calorie intake increases or physical activity decreases, weight loss naturally slows regardless of medication.
- Metabolic adaptation: As you lose weight, your body requires fewer calories to maintain that lower weight, naturally reducing the deficit.
- Appetite hormone changes: Some individuals develop a tolerance to GLP-1 receptor signalling, though research is ongoing.
Clinical data from the SURMOUNT trials showed sustained weight loss over 72 weeks, but individual responses vary. Some people benefit from dose increases; others may need to review diet and exercise patterns with their healthcare provider.
Clinically BackedWeight Loss
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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.
Accessing Mounjaro in the UK: NHS vs Private Routes
NHS access: NICE has approved tirzepatide (Mounjaro) for use within NHS specialist weight management services. You'll need referral from your GP to a tier 3 or tier 4 weight management service. Availability and waiting times vary significantly by region and ICB (Integrated Care Board). Some areas have long waiting lists.
Private access: Available through UK-licensed prescribers via online consultation, dispensed by GPhC-registered pharmacies. No NHS referral needed. Costs typically range from £129–£320+ per month depending on your current dose. A prescriber will assess your eligibility — you'll need a BMI of 30 or above, or 27–29.9 with weight-related health conditions such as type 2 diabetes, hypertension, or cardiovascular disease.
Whichever route you choose, a prescriber will guide dose management and monitor your progress.
- 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.
Can I increase my Mounjaro dose if weight loss slows?
Yes. The standard Mounjaro dose titration allows escalation from 2.5 mg up to 15 mg weekly. However, dose increases must be prescribed and managed by your healthcare provider. If you're on a private prescription, discuss this with your prescriber. On the NHS, your specialist team will guide dosing decisions.
Is Mounjaro ineffective after a few months?
Not necessarily. Plateaus are normal in weight loss. Your body adapts, and your prescriber may adjust your dose. The SURMOUNT trials demonstrated sustained effects over 72 weeks, but lifestyle factors also matter. Your GP or prescriber can help troubleshoot and explore whether increasing your dose or reviewing diet and exercise is appropriate.
How much does Mounjaro cost privately in the UK?
Private Mounjaro costs typically range from £129–£320+ per month depending on your current dose (2.5 mg to 15 mg). Prices vary between providers. Always check that you're using a GPhC-registered pharmacy and that your prescription comes from a UK-licensed prescriber.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro clinical trials showed average weight loss of 15–21% body weight; Wegovy showed approximately 15%. Both are prescription-only and require clinical assessment. Individual results vary significantly.
Can my GP prescribe Mounjaro privately if I don't want NHS waiting lists?
Your GP can only prescribe Mounjaro on the NHS through the specialist pathway. For private prescription, you'll need to access an online consultation with a UK-licensed prescriber (not necessarily your GP). They'll assess your eligibility, issue a prescription, and a GPhC-registered pharmacy will dispense it.
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.