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 Isn't Mounjaro Working For Me?
If you're on Mounjaro (tirzepatide) and weight loss has slowed, stalled, or hasn't started, you're not alone. Many people experience plateaus or slower-than-expected results. This doesn't mean the medication has failed — several factors affect how well Mounjaro works, from dose level to lifestyle, metabolism, and individual body response. Understanding why can help you and your GP adjust your approach and get back on track.
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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.
Common Reasons Mounjaro May Not Be Working As Expected
You may still be on a low starting dose. Mounjaro begins at 2.5 mg weekly and increases gradually — the full effect typically isn't seen until doses of 10 mg or higher. If you've only recently started or just increased your dose, your body may still be adjusting. It can take 4–8 weeks at each dose level to see significant changes.
You're not in a calorie deficit. Mounjaro helps reduce appetite and cravings, but it doesn't create weight loss on its own. Without eating fewer calories than you burn, the medication cannot produce results. Even with reduced hunger, portion sizes and food choices still matter. Use our GLP-1 weight loss calculator to estimate realistic projections based on your current intake.
Lifestyle hasn't changed enough. Weight loss plateaus are common after 3–6 months because your metabolism adapts. Increasing physical activity, varying your exercise, or adjusting your diet can restart progress. The medication alone is not sufficient — it's a tool to support behaviour change, not a replacement for it.
Individual variation. Clinical trials showed average weight loss of 15–21% at maximum doses, but some people lose less. Genetics, hormones, underlying health conditions (like thyroid issues or PCOS), and medications can all affect response.
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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 Delivering Results
Review your current dose. If you're below 10 mg weekly, ask your GP or prescriber whether you're eligible to increase. Most significant weight loss occurs at 10 mg and above. Dose increases happen every 4 weeks minimum, so patience is important.
Assess your diet honestly. Track your food intake for a week — many people underestimate calories consumed. A moderate calorie deficit (around 500 kcal/day) alongside Mounjaro typically produces 0.5–1 kg weekly loss. Our BMI calculator can show your healthy weight target; work backwards from there.
Speak to your prescriber or GP. If weight loss has completely plateaued for 8+ weeks at a stable dose, it's worth reviewing. They can check for underlying causes, medication interactions, or whether a dose adjustment is appropriate. Don't stop taking Mounjaro without guidance — always discuss changes with your healthcare team.
- 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 work?
Weight loss typically becomes noticeable at doses of 5 mg and above, with most significant results at 10–15 mg. Since Mounjaro starts at 2.5 mg and increases every 4 weeks, it can take 12–20 weeks to reach effective doses. Individual responses vary — some people see results within weeks, others take longer. Patience is essential.
Can you become resistant to Mounjaro?
True resistance is rare, but weight loss plateaus are common after 3–6 months as your metabolism adapts. This is normal with any weight loss method. Breaking a plateau often requires increasing physical activity, adjusting your diet further, or occasionally increasing your Mounjaro dose if medically appropriate.
Why am I not losing weight on Mounjaro despite reduced appetite?
Reduced appetite doesn't automatically equal weight loss — you still need to eat fewer calories than you burn. Some people unconsciously choose calorie-dense foods or don't reduce portion sizes enough. Appetite suppression is a tool that makes calorie reduction easier, but you must use it actively.
Should I stop Mounjaro if it's not working?
No — stopping abruptly isn't recommended. If you've been on a stable dose for 12+ weeks with no progress, speak to your prescriber first. They may adjust your dose, review your lifestyle, or check for underlying health issues. Stopping should only happen under medical guidance.
What's the difference between Mounjaro and Wegovy if I'm not seeing results?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro showed slightly higher average weight loss in trials (15–21% vs. 15% for Wegovy), but individual responses differ. Some people respond better to one than the other, though switching requires a prescriber's assessment.
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.