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 has stopped working, you're not alone — weight loss plateaus and reduced effectiveness are common experiences on GLP-1 and GIP receptor agonist medications. This can happen for several reasons: your body may have adapted to the medication, dose tolerance may have developed, lifestyle factors may have shifted, or your individual physiology may require a different approach. Understanding why this happens and exploring your options — including whether Wegovy or other interventions might suit you better — is important. Always discuss any changes with your prescriber before making adjustments.
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.
Understanding Mounjaro Effectiveness and Tolerance
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist that works by activating two natural hormone pathways to regulate appetite and support weight loss. In the SURMOUNT-1 clinical trial, participants on 15mg Mounjaro lost an average of 20.9% of their body weight over 72 weeks — but this doesn't mean results continue indefinitely at the same rate.
Why effectiveness may plateau:
- Dose tolerance: Your body adapts to the medication over time, meaning the same dose may become less effective. Your prescriber may recommend increasing your dose (up to the maximum of 15mg weekly) or exploring a different medication entirely.
- Weight loss resistance: As you lose weight, your metabolic rate adjusts, making further loss harder — this is natural physiology, not a medication failure.
- Lifestyle drift: Even small changes in diet or activity levels can offset medication benefits. Weight loss medications work alongside reduced-calorie diet and increased physical activity, not instead of them.
- Individual variation: Some people naturally respond less robustly to GLP-1 mechanism medications, making them better suited to alternative approaches.
If you're on a lower dose (5mg or 10mg), your prescriber may increase your Mounjaro dose gradually — each dose increase typically takes 4 weeks to assess effectiveness.
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.
Mounjaro vs Wegovy: Different Mechanisms for Different People
Mounjaro and Wegovy work differently: Mounjaro is a dual GIP + GLP-1 agonist, activating two hormone pathways, whilst Wegovy (semaglutide) is a GLP-1 only agonist. In clinical trials, Mounjaro showed slightly higher average weight loss (20.9% at maximum dose) compared to Wegovy (approximately 14.9%), but individual results vary enormously. Some people find Wegovy more effective if they've plateaued on Mounjaro, whilst others experience better results staying on Mounjaro at a higher dose.
If your Mounjaro has stopped working, switching to Wegovy is one option your prescriber may consider — though this requires a fresh clinical assessment. The approximate dose equivalence is roughly Mounjaro 15mg ≈ Wegovy 2.4mg, but any switch must be managed by your prescriber. Use our free GLP-1 weight loss calculator to explore potential outcomes with different approaches, and discuss your options with your GP or weight management specialist before making changes.
- 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 just increase my Mounjaro dose if it stops working?
Possibly — if you're not at the maximum 15mg dose, your prescriber may recommend a gradual increase (minimum 4 weeks at each dose). However, if you're already at 15mg or have been on the same dose for several months without progress, increasing further isn't an option. Your prescriber may suggest other strategies like reviewing your diet and activity, or exploring alternative medications such as Wegovy.
Is it normal for Mounjaro to stop working after a few months?
Yes, weight loss plateaus are common on any weight loss medication. This reflects natural body adaptation and metabolic adjustment — not a failure of the medication. Many people experience rapid initial loss followed by a slower phase. Continuing the medication often maintains your weight loss even if the rate slows, preventing regain.
What's the difference between Mounjaro and Wegovy?
Mounjaro is a dual GIP + GLP-1 agonist (mechanism of two hormones), whilst Wegovy is GLP-1 only. Mounjaro showed average weight loss of 20.9% in trials versus Wegovy's 14.9%, but individual responses vary. Some people respond better to one than the other — if Mounjaro has plateaued, switching to Wegovy is an option your prescriber can assess.
Will my prescriber switch me to Wegovy if Mounjaro stops working?
It depends on your individual situation. Your prescriber will consider factors like your current dose, how long you've been on the medication, lifestyle factors, and your health profile. A switch to Wegovy is possible, but other options include dose optimisation, lifestyle reassessment, or a short break before restarting. Always discuss your concerns with your prescriber before making changes.
How long should I give Mounjaro before deciding it's stopped working?
Weight loss typically happens over weeks and months, not days. If you've been on a stable dose for 8–12 weeks without any progress, and you're confident your diet and activity haven't changed, it may be worth discussing with your prescriber. However, continued weight maintenance (no regain) is still a benefit of the medication, even if new weight loss has slowed.
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.