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 Has Stopped Working — What This Means and Your Options
If you've been taking Mounjaro and notice your weight loss has plateaued or stopped, you're not alone — this is a common experience. Weight loss plateaus can happen for several reasons, from your body adapting to the medication to lifestyle factors that need adjustment. Understanding why this happens and knowing your options — whether that's a dose adjustment, lifestyle review, or exploring alternatives like Wegovy — can help you move forward. This guide covers what to do if Mounjaro has stopped working for you and how to access support in the UK.
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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 on Mounjaro
Weight loss plateaus are normal and don't necessarily mean Mounjaro has stopped working. Several factors can contribute to this:
- Dose tolerance: Your body may adapt to your current dose of tirzepatide over time, meaning your prescriber might suggest increasing to the next dose level (up to the maximum of 15 mg weekly).
- Calorie intake creep: Portion sizes or snacking may gradually increase as the appetite-suppressing effects of Mounjaro reduce nausea and GI side effects improve.
- Reduced physical activity: Changes in exercise routine or daily movement can slow weight loss, even on medication.
- Water retention or muscle gain: The scale may not reflect positive changes if you're building muscle or retaining fluid.
- Underlying health factors: Thyroid issues, hormonal changes, or other medical conditions can affect weight loss progress.
The best first step is to discuss your progress with your prescriber or GP, who can review your dosing schedule and lifestyle factors.
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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 Support and Considering Your Options in the UK
If you're experiencing a weight loss plateau on Mounjaro, several options are available in the UK:
- Dose adjustment: If you're not yet on the maximum 15 mg weekly dose, your prescriber may recommend titrating to a higher dose.
- Lifestyle review: A GP or dietitian can help identify diet and exercise adjustments to restart weight loss.
- Continue current treatment: Some weight loss plateaus are temporary; consistency over time often leads to further progress.
- Alternative medication: If Mounjaro isn't delivering the results you need, your prescriber might explore alternatives like Wegovy (semaglutide), which works via a single GLP-1 pathway rather than Mounjaro's dual GIP/GLP-1 mechanism.
Use our free GLP-1 weight loss calculator to compare projected outcomes at different doses, and track your progress with our progress tracker to identify patterns.
- 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.
How long should I stay on my current Mounjaro dose before assuming it's not working?
Most prescribers recommend staying on each dose for a minimum of 4 weeks before titrating. Weight loss is rarely linear — plateaus lasting 2–4 weeks are normal. Before assuming the medication has stopped working, give it 6–8 weeks at your current dose, track your weight consistently using our progress tracker, and review your diet and activity with your GP.
Can I switch from Mounjaro to Wegovy if Mounjaro isn't working?
Yes, switching between GLP-1 medications is possible, though any change must be managed by your prescriber. Wegovy uses semaglutide, a single GLP-1 agonist, whereas Mounjaro is a dual GIP/GLP-1 agonist — some people respond better to one mechanism than the other. Your GP or prescriber can assess whether a switch is appropriate based on your individual response and health.
Should I expect my weight loss to continue indefinitely on Mounjaro?
No. Most people experience the most significant weight loss in the first 6–12 months, then weight loss typically slows or plateaus as your body reaches a new equilibrium. This is normal and not a sign the medication has failed. Mounjaro is designed to help you reach and maintain a healthier weight alongside lifestyle changes, not to produce continuous weight loss indefinitely.
What should I ask my GP if Mounjaro has stopped working?
Ask about your current dose and whether you're eligible for a dose increase; discuss your diet, activity level, and whether adjustments might help; explore whether an underlying health condition (thyroid, hormones, medication side effects) could be contributing; and ask whether alternatives like Wegovy or other treatment options might be considered if progress truly stalls.
Is a weight loss plateau the same as Mounjaro not working?
Not necessarily. A plateau is a temporary slowdown or pause in weight loss — very common and often temporary. Mounjaro "not working" would mean no weight loss at all after several months at adequate doses. Most plateaus resolve with dose adjustment, lifestyle review, or simply continuing the medication. If no weight loss has occurred after 3–4 months at therapeutic doses, discuss alternatives with your prescriber.
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.