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 Am I Not Losing Weight on Mounjaro?
Not seeing weight loss results on Mounjaro can be frustrating, but it's important to understand that individual responses to tirzepatide vary significantly. Weight loss on Mounjaro depends on several factors including your current dose, how long you've been taking it, your diet and activity level, and your individual metabolism. Most people experience the most noticeable changes during the dose titration phase, and results continue to develop over 16–20 weeks. If you're not losing weight, there are practical steps you and your prescriber can take to support better outcomes.
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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.
Common Reasons for Slower Weight Loss on Mounjaro
Several factors can affect how much weight you lose on Mounjaro (tirzepatide), even when taking it correctly:
- You're still in dose titration. Mounjaro starts at 2.5 mg and increases every 4 weeks (2.5 mg → 5 mg → 7.5 mg → 10 mg → 12.5 mg → 15 mg). Many people see minimal weight loss until reaching a therapeutic dose of 10 mg or higher. If you've only recently started or recently increased your dose, give it 4 weeks to fully take effect.
- Your diet hasn't changed enough. Mounjaro reduces appetite and helps you feel fuller, but it's not a substitute for dietary changes. If you're still consuming excess calories—even with reduced appetite—weight loss will be slower. Clinical trials showed Mounjaro works best alongside a reduced-calorie diet and increased physical activity.
- You're not moving enough. Physical activity amplifies weight loss results. Even without formal exercise, increasing daily movement (walking, stairs, fidgeting) supports better outcomes.
- Individual metabolism varies. Some people naturally lose weight faster than others on the same dose. Genetics, hormones, age, and underlying health conditions all play a role.
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.
What You Can Do to Support Better Results
If you're on Mounjaro but not seeing the weight loss you expected, speak to your prescriber. They may suggest:
- Continuing to your next dose increase if you haven't yet reached 10 mg—many people see significant changes once reaching higher therapeutic doses.
- Reviewing your diet with a healthcare professional or dietitian to identify where calories may be hiding.
- Checking for underlying issues such as thyroid problems, medication interactions, or hormonal changes that could slow weight loss.
- Confirming you're injecting correctly and storing your Mounjaro KwikPen properly—storage errors or injection technique issues can reduce effectiveness.
Weight loss on Mounjaro is individual. Use our free GLP-1 weight loss calculator to see projected timelines at different doses, and track your progress with our progress tracker to spot trends over weeks rather than days.
- 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 to see weight loss on Mounjaro?
Most people see noticeable weight loss between weeks 8–16 once they've reached a therapeutic dose (usually 10 mg or higher). Clinical trials showed the most significant changes occurred between weeks 12–72. If you've only been on a starter dose for 2–4 weeks, you may not yet see major changes—this is normal and expected during dose titration.
Does Mounjaro stop working over time?
Mounjaro effectiveness typically continues throughout treatment, though some people plateau after initial weight loss. This can happen if calorie intake increases as appetite returns slightly, or if your body adapts to the medication. Speaking to your prescriber about dose adjustments or lifestyle changes can help restart progress.
Can I speed up weight loss on Mounjaro by eating less?
Very restrictive eating is not recommended and can be unsafe. Mounjaro works best with a moderate calorie deficit (around 500 kcal/day) combined with adequate nutrition and physical activity. Eating too little can cause muscle loss, nutrient deficiencies, and fatigue. Your GP or a dietitian can help you find a sustainable approach.
Is Mounjaro vs Wegovy better for weight loss?
Mounjaro and Wegovy are different medications. Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist, while Wegovy (semaglutide) is a GLP-1 agonist only. Clinical data shows Mounjaro may produce slightly greater average weight loss (~20.9% vs ~14.9%), but individual results vary considerably. Your prescriber can advise which is more suitable for you.
What if I'm on the maximum Mounjaro dose and still not losing?
If you're at 15 mg and weight loss has stalled, speak to your prescriber. They may investigate underlying health conditions, medication interactions, or hormonal factors. Sometimes switching to a different medication or combining approaches yields better results. Weight loss is individual, and not everyone loses at the same rate—focus on health markers like blood pressure and energy rather than scale weight alone.
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.