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 Mounjaro May Not Be Causing Weight Loss
If you're taking Mounjaro but not seeing weight loss, you're not alone — weight loss plateaus are common with GLP-1 and GIP/GLP-1 medications. This could be due to several reasons: you may need a dose increase, your body may have adapted, or lifestyle factors may need adjustment. Understanding why weight loss has stalled is the first step to getting back on track. Always discuss any concerns with your prescriber, as they can assess your individual situation and adjust your treatment plan accordingly.
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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 Weight Loss Plateaus on Mounjaro
Weight loss plateaus are a normal part of the weight management journey, even with prescription medication like Mounjaro (tirzepatide). Several factors may explain why you're not losing weight:
- Insufficient dose: If you're on a lower dose (2.5 mg, 5 mg, or 7.5 mg), your body may respond better to escalation. NHS guidance recommends remaining on each dose for at least 4 weeks before increasing, and some people require the higher doses (10 mg, 12.5 mg, or 15 mg) for optimal effect.
- Metabolic adaptation: As you lose weight, your metabolic rate naturally decreases — your body requires fewer calories. This is why calorie intake needs to be reassessed periodically.
- Dietary drift: Over time, portion sizes or food choices may gradually increase without you noticing. Keeping a food diary can help identify this.
- Reduced physical activity: Lower activity levels will slow weight loss, even with medication.
- Medication timing or technique: Incorrect injection technique or storage can affect how well the medication works. Ensure you're injecting into the correct site (abdomen, thigh, or upper arm) and rotating sites weekly.
- Medical factors: Thyroid conditions, PCOS, or other endocrine disorders can affect weight loss. Your GP can check for these if relevant.
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.
Next Steps — When to Speak to Your Prescriber
If you've been on Mounjaro for 8–12 weeks without any weight loss, contact your prescriber or the NHS specialist weight management team managing your care. They can review your dose, assess whether dose escalation is appropriate, and check that lifestyle changes (reduced-calorie diet and physical activity) are in place. Use our free BMI calculator to track your current BMI and establish a baseline — even small reductions in BMI can indicate progress. Your prescriber may also want to rule out underlying medical factors. Remember: individual results vary significantly, and some people may not respond as expected to any weight loss medication. If Mounjaro isn't working after proper escalation and lifestyle adherence, your prescriber can discuss alternative options.
- 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 wait before expecting weight loss on Mounjaro?
Clinical trials showed meaningful weight loss typically begins within 8–12 weeks of starting Mounjaro, though individual timelines vary. However, you should be on your final maintenance dose (usually 15 mg) for at least 8 weeks before concluding it's not working for you. If no weight loss has occurred after 12 weeks at the maintenance dose alongside a reduced-calorie diet and increased physical activity, contact your prescriber.
Could my dose be too low?
Yes. Mounjaro doses range from 2.5 mg (starting) to 15 mg (maximum). If you're on 5 mg or 7.5 mg, your prescriber may recommend escalation. Each dose increase should occur at least 4 weeks apart. The 15 mg once-weekly dose is the standard maintenance dose used in clinical trials and may be where you need to be for weight loss.
Is it normal to stop losing weight after initial loss on Mounjaro?
Yes, weight loss plateaus are very common. Your body adapts to lower calories, metabolism adjusts, and lifestyle factors may have shifted. This doesn't mean Mounjaro has stopped working — it means your calorie intake or activity level may need reassessment. Your prescriber or a dietitian can help adjust your plan.
What lifestyle changes should I make alongside Mounjaro?
Mounjaro works alongside a reduced-calorie diet (typically 500 kcal below your normal intake) and increased physical activity. Aim for a balanced diet with adequate protein, regular movement, and strength training if possible. NHS weight management services can provide specific guidance tailored to your needs.
Should I stop Mounjaro if it's not causing weight loss?
No — do not stop without speaking to your prescriber first. There may be adjustments to make, or your prescriber needs to assess whether this is the right medication for you. Stopping suddenly without medical guidance is not recommended. Always discuss your concerns with your prescriber.
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.