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
Mounjaro Didn't Work For Me — What You Should Know
If Mounjaro hasn't helped you lose weight, you're not alone — individual responses to weight loss medication vary significantly. Some people see excellent results, while others experience minimal weight loss or find the medication stops working after an initial period. This doesn't mean there's something wrong with you. There are several legitimate reasons why Mounjaro may not be producing the results you expected, and important steps you can take next. Your GP or prescriber can help determine whether to continue, adjust your dose, or explore other options suitable for your circumstances.
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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 As Expected
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, and while clinical trials showed average weight loss of 15–21% of body weight, the word "average" is key — results vary dramatically between individuals. Several factors affect whether Mounjaro works for you:
- Insufficient dose: You may not be on a high enough dose yet. Mounjaro is titrated (increased) gradually from 2.5 mg up to a maximum of 15 mg, with a minimum of 4 weeks at each dose. Some people need higher doses to see results. Your prescriber may recommend continuing titration before concluding it's not working.
- Lifestyle factors unchanged: Mounjaro works alongside dietary changes and physical activity, not instead of them. If calorie intake hasn't reduced or exercise hasn't increased, weight loss may stall despite the medication.
- Metabolic adaptation: Your body may have adapted to the medication — initial weight loss sometimes plateaus after 6–12 months, a normal physiological response.
- Underlying medical conditions: Conditions like hypothyroidism, PCOS, or uncontrolled diabetes may reduce weight loss effectiveness. Your GP should have screened for these, but discussing them again may help.
- Medication interactions: Other medications you're taking might affect absorption or efficacy. Always ensure your prescriber knows all medications you use.
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.
What to Do If Mounjaro Isn't Working
Don't stop taking Mounjaro suddenly without speaking to your prescriber. Your next steps depend on where you are in your treatment:
- If you're below 15 mg: Ask your prescriber about continuing dose titration — you may not have reached your optimal dose yet.
- If you're at 15 mg with no results: Discuss with your GP whether to continue (it may take 12+ weeks to see results) or explore alternatives like Wegovy (semaglutide), which is also available through NHS specialist services or private prescription in the UK.
- Review lifestyle with your prescriber: Ensure you're in a calorie deficit and getting adequate physical activity.
- Check for underlying conditions: Ask for screening for thyroid function, blood sugar control, and other factors that influence weight loss.
- Consider the timeframe: Weight loss with GLP-1 medications takes time — give it at least 12 weeks at your current dose before assuming it's not working.
Your prescriber is there to support you. Be honest about your progress and concerns.
- 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 it take for Mounjaro to start working?
Weight loss with Mounjaro typically becomes noticeable after 4–8 weeks, though some people see results earlier or later. Clinical trials measured weight loss over 72 weeks, and results accumulate over time. If you've been on a stable dose for fewer than 12 weeks, continue as directed and monitor progress. Your GP can review results at each visit.
Should I stop taking Mounjaro if it's not working?
No — never stop Mounjaro suddenly without speaking to your prescriber. They may recommend dose adjustment, extending your timeframe, reviewing lifestyle factors, or switching to an alternative. Abruptly stopping can also cause side effects. Always consult your GP or prescriber before making changes.
Can I switch from Mounjaro to Wegovy if Mounjaro didn't work?
Possibly, yes. Mounjaro and Wegovy are different medications — Mounjaro is a dual GIP+GLP-1 agonist, whilst Wegovy (semaglutide) is a GLP-1 agonist only. Some people respond better to one than the other. Your prescriber can assess whether a switch is appropriate based on your situation and any side effects you've experienced.
Is Mounjaro being ineffective a sign I need bariatric surgery?
Not necessarily. Weight loss medication is tier 3 in the NHS pathway — bariatric surgery (tier 4) is typically considered only after other options have been exhausted and for severe obesity with significant health complications. Your GP can discuss all available options with you in order.
Could my other medications be stopping Mounjaro from working?
Possibly. Some medications affect how the stomach empties or how nutrients are absorbed, which can reduce GLP-1 effectiveness. Oral contraceptives are affected by Mounjaro (requiring barrier methods for 4 weeks after dose increases). Always tell your prescriber about all medications so they can assess potential interactions.
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.