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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What To Do If Mounjaro Didn't Work For You
If Mounjaro hasn't delivered the weight loss results you expected, you're not alone — individual responses to tirzepatide vary significantly. Some people find it highly effective, whilst others experience minimal weight loss despite being on the maximum dose. This guide explains why Mounjaro may not work for everyone, what factors affect its effectiveness, and what alternatives you can explore through the NHS or private prescribing 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 Mounjaro May Not Be Working For You
Mounjaro (tirzepatide) is effective for many people, but individual results vary dramatically — not everyone loses significant weight on this medication. Several factors influence whether tirzepatide works well for you:
- Dose too low: You may still be in the titration phase. Mounjaro takes 4 weeks minimum at each dose before increasing, and many people need the higher doses (10mg, 12.5mg, or 15mg) to see substantial results. If you're on 2.5mg or 5mg, ask your prescriber about progressing to the next dose.
- Genetic variation: Some people have natural variations in GLP-1 receptor sensitivity, meaning they respond less dramatically to GLP-1 or GIP agonists regardless of dose.
- Medical conditions: Type 2 diabetes, PCOS, hypothyroidism, or certain medications (including some antidepressants) can reduce weight loss effectiveness.
- Lifestyle factors: Mounjaro works alongside reduced-calorie diet and physical activity. Without these changes, medication results are limited. Use our free GLP-1 weight loss calculator to understand expected results with your current dose and lifestyle.
- Duration: Weight loss typically plateaus after 6–12 months on a stable dose. If you've been on Mounjaro for less than 12 weeks, you may still be in the adjustment period.
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.
NHS And Private Options If Mounjaro Isn't Working
If Mounjaro has failed to deliver results after being on the maximum dose (15mg) for at least 12 weeks, discuss alternatives with your prescriber. NHS options include:
- Switching to Wegovy (semaglutide) — a different GLP-1 agonist that works via a single mechanism rather than the dual GIP+GLP-1 action of Mounjaro. Some people respond better to semaglutide.
- Trying Saxenda (liraglutide) — an older GLP-1 injection given daily (rather than weekly). Fewer people use this now, but it's still NHS-available in some areas.
- Referral to specialist services for additional support, dietary assessment, or consideration of other weight management approaches.
Privately, you can access Wegovy or continue exploring other options. Always discuss medication switches with your prescriber, as individual health factors matter.
- 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 Mounjaro before deciding it's not working?
The SURMOUNT clinical trials assessed results at 72 weeks. Most prescribers recommend staying on your current dose for at least 12 weeks before concluding it's ineffective. If you're still in dose titration (starting doses), weight loss typically accelerates as you increase. If you're on 15mg (the maximum) for 12+ weeks with minimal loss, it may not be the right medication for you.
Could my other medications be stopping Mounjaro from working?
Yes. Certain medications can interfere with weight loss, including some antidepressants, corticosteroids, and medications that affect appetite regulation. Some conditions like hypothyroidism or uncontrolled type 2 diabetes can also blunt results. Discuss all your medications and health conditions with your prescriber — they may adjust dosing or switch you to alternatives.
Is Wegovy more effective than Mounjaro if Mounjaro didn't work?
Not necessarily. Wegovy (semaglutide) works differently — it's a single GLP-1 agonist rather than a dual GIP+GLP-1 agonist. Some people respond better to one mechanism than the other, but there's no way to predict this beforehand. Switching to Wegovy is a reasonable next step to try. Clinical trial data shows similar average weight loss between the two, but individual variation is high.
What if I want to try a different weight loss approach instead of another injection?
Discuss alternatives with your GP or specialist. Options include referral to NHS tier 3 weight management services (which may offer intensive dietary support), structured diet programmes, or bariatric surgery if you meet criteria. Your BMI, health conditions, and previous attempts matter. Use our free BMI calculator to understand where you sit on the NHS eligibility scale.
Can I switch from Mounjaro to Wegovy immediately, or is there a wait?
This depends on your prescriber. Generally, you can switch between medications without a gap, though some prescribers may recommend a brief washout period. If accessing privately, you can apply for a Wegovy prescription. If through the NHS, your specialist service will advise on switching protocols. Always get prescriber approval before stopping or switching any medication.
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.