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
Why Has My Mounjaro Stopped Working?
If your Mounjaro (tirzepatide) has stopped working, you're not alone — many people experience a plateau in weight loss after initial results. This can happen for several reasons, including reaching a dose plateau, lifestyle drift, or your body adapting to the medication. Whether you're accessing Mounjaro through the NHS or privately, understanding why this happens and what your options are is essential. This guide explains the common reasons, how to discuss it with your prescriber, and what the cost and access implications are in the UK.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Common Reasons Mounjaro May Stop Working
Weight loss plateaus are a normal part of the weight management journey. Several factors can contribute to Mounjaro appearing to stop working:
- Dose plateau: You may have reached a dose level where your body has adapted to the medication's effects. Increasing to the next dose (from 10mg to 12.5mg, or 12.5mg to 15mg) may help restart weight loss.
- Lifestyle drift: If calorie intake has gradually increased or physical activity has decreased, weight loss will slow even with medication. Your reduced-calorie diet and exercise routine remain essential.
- Medication tolerance: Your body may adapt to the tirzepatide dose over time, reducing its appetite-suppressing effect. This is why dose escalation (moving through 2.5mg, 5mg, 7.5mg, 10mg, 12.5mg, to 15mg) is built into Mounjaro's treatment protocol.
- Inadequate dose for your needs: If you're not yet on the maximum 15mg dose, your prescriber may recommend escalating further.
- Medical factors: Thyroid issues, hormonal changes, or other health conditions may affect weight loss. Your GP can investigate these if relevant.
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.
NHS vs Private: Cost, Access, and Next Steps
NHS route: If you're receiving Mounjaro through an NHS specialist tier 3 weight management service, discuss the plateau with your prescriber before your next injection. They can assess whether dose escalation is appropriate or suggest other interventions. There is no additional cost at point of use, though NHS availability varies significantly by region and waiting lists can be long.
Private route: If you're accessing Mounjaro through a private online prescription, most costs range from £129–£200 per month depending on your current dose. A dose increase typically incurs a higher monthly cost. An online consultation with a UK-licensed prescriber (usually £20–£50) is required to request a dose change. Your prescriber will assess whether escalation is safe and appropriate before issuing a new prescription. Verify your provider is GPhC-registered before paying.
- 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 it's stopped working?
Possibly. If you're not yet on the maximum 15mg once-weekly dose, your prescriber may recommend escalation. Each dose increase requires a minimum of 4 weeks on the current dose before progressing. Discuss this at your next appointment or consultation — your prescriber will assess whether it's clinically appropriate for you.
How much does a Mounjaro dose increase cost in the UK?
If accessing privately, costs typically rise with higher doses, ranging from approximately £129–£200 per month. A higher dose (such as 15mg) will usually cost more than a lower dose (such as 5mg). Always check your specific provider's pricing before requesting a dose change. Private prescriptions require a new online consultation.
Is Mounjaro available on the NHS if it stops working?
Yes, but access is limited to NHS tier 3 specialist weight management services through referral from your GP. Availability, waiting lists, and criteria vary significantly across UK regions and ICBs. If you're already on NHS Mounjaro and it plateaus, discuss options with your specialist service — they can assess escalation or alternative approaches.
Could something else explain my weight loss plateau?
Yes. Even with Mounjaro, calorie intake, physical activity, sleep quality, stress, and underlying health conditions all affect weight loss. Use our GLP-1 weight loss calculator to reassess your projected timeline and discuss lifestyle factors with your GP or prescriber. A plateau doesn't always mean the medication has failed.
What's the difference between Mounjaro and Wegovy if one stops working?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Some people respond better to one than the other, but switching requires a new clinical assessment and prescription. Your prescriber can discuss whether a switch might be appropriate if dose escalation hasn't worked.
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.