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 weight loss has plateaued on Mounjaro (tirzepatide), you're not alone — many people experience a slowdown in results after initial weight loss. This is a normal physiological response called weight loss adaptation. Your body becomes more efficient at the current dose, which is why your prescriber may adjust your UK prescription or recommend lifestyle changes. Understanding what's happening and knowing your NHS and private options can help you move forward.
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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.
Weight Loss Plateaus on Mounjaro — What's Normal
A weight loss plateau on Mounjaro is when your weight stabilises despite continuing the same dose. This typically happens after 12–16 weeks of steady results and occurs because your body adapts to the medication. This is not treatment failure — it's a normal biological response. When you lose weight, your metabolic rate decreases, and your body becomes more efficient at managing the dose you're taking.
In the SURMOUNT clinical trials, participants experienced significant weight loss in the first 4–6 months, followed by a plateau phase where results slowed but continued. Your prescriber may increase your tirzepatide dose gradually to restart weight loss — the standard Mounjaro KwikPen allows doses from 2.5 mg up to 15 mg once weekly. If you're already on the maximum dose, adjustments focus on dietary consistency and physical activity. Use our free GLP-1 weight loss calculator above to understand typical dose-related outcomes, and track progress with our free progress tracker to identify patterns over time.
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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.
NHS vs Private Options When Mounjaro Results Slow
NHS route: If you're receiving Mounjaro through an NHS tier 3 specialist weight management service, your prescriber will monitor your progress at regular appointments (typically 4–12 weekly). If you've plateaued, they can assess whether a dose increase is appropriate, or discuss dietary and exercise adjustments. NHS access to Mounjaro continues to expand following NICE approval, though regional availability and waiting times vary significantly across England, Scotland, Wales, and Northern Ireland.
Private route: If prescribed privately, you can contact your prescriber to discuss plateau management. Many private online prescribing services offer follow-up consultations to review progress and adjust doses. Costs for dose increases depend on your provider. Consider using our free BMI calculator and weight converter to track your metrics in both UK measurements (stone and pounds) and metric, which can help your prescriber assess your progress.
When to Contact Your GP or PrescriberContact your GP or prescriber if your weight hasn't changed for 8+ weeks, or if you have concerns about side effects that might be preventing further weight loss. Don't assume Mounjaro has "stopped working" — weight loss is not linear, and a plateau of several weeks is expected. Your prescriber may recommend increasing your dose if medically appropriate, or may pause increases if you're managing side effects. If you're on a high dose and still plateauing, discussion should focus on lifestyle factors: calorie intake, physical activity, sleep quality, and stress. Weight loss medications work best alongside sustained dietary changes and increased movement — medication supports this process but doesn't replace it.
- 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 does a Mounjaro plateau usually last?
Plateaus typically last 4–12 weeks and are normal. Your body adapts to your current dose. Most people see results restart after a dose increase or with renewed focus on diet and exercise. If your plateau continues beyond 12 weeks with no change, contact your prescriber to review your plan.
Will increasing my Mounjaro dose restart weight loss?
Often yes — dose increases can restart weight loss in many people. Your prescriber will assess whether this is safe for you. Not everyone responds to dose increases, and some people plateau even at the maximum 15 mg dose. Lifestyle factors then become the priority.
What's the difference between a plateau and Mounjaro not working?
A plateau is temporary weight stability despite continued medication — this is normal. Mounjaro "not working" would mean no weight loss from the start. If you've lost weight initially and then plateaued, your medication is working as expected and you're experiencing normal adaptation.
Can I switch from Mounjaro to Wegovy if I've plateaued?
This requires prescriber assessment. Wegovy (semaglutide) uses a different mechanism as a single GLP-1 agonist, whereas Mounjaro is a dual GIP+GLP-1 agonist. Switching may help some people, but there's no assures. Any medication change must be managed by your prescriber.
What should I discuss with my NHS prescriber about my plateau?
Discuss: how long the plateau has lasted, your current diet and activity levels, any new side effects, and whether a dose increase is appropriate for you. Ask about referral to a dietitian if available through your NHS weight management service. Bring a food diary and activity log to help your prescriber assess your situation.
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.