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 Haven't I Lost Weight on Mounjaro?
If you're taking Mounjaro and not seeing weight loss yet, you're not alone — and there are several reasons this might be happening. Weight loss on any weekly weight loss injection varies significantly between individuals, and the timeline depends on your dose, how long you've been taking it, and lifestyle factors. Understanding what affects your results can help you decide whether to continue, adjust your approach, or speak to your prescriber about next steps.
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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 Slow or Absent Weight Loss on Mounjaro
You may not be on the right dose yet. Mounjaro requires gradual dose escalation — you start at 2.5 mg and increase by 2.5 mg every 4 weeks until you reach an effective dose (typically 10–15 mg). If you've only been taking it for a few weeks on a low dose, your body may not yet be responding optimally. Clinical trials showed meaningful weight loss took 12–16 weeks to become noticeable.
Lifestyle changes haven't been fully implemented. Mounjaro works alongside a reduced-calorie diet and increased physical activity — it's not a replacement for these. If you're not in a calorie deficit, weight loss will be minimal regardless of medication. The KwikPen is a tool to support behaviour change, not to work in isolation.
You may have reached a weight loss plateau. Even with medication, your body may temporarily pause weight loss as it adjusts. This is normal and usually temporary. Plateaus lasting 2–4 weeks don't mean the medication has stopped working.
Your dose may need adjusting. If you've been on the same dose for 8+ weeks with no progress, your prescriber may recommend dose titration to a higher level to find your optimal response.
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.
Accessing Mounjaro and Managing Cost in the UK
In the UK, Mounjaro is available through two main routes: NHS specialist weight management services and private prescription through online prescribers. NHS access is limited and varies by region — waiting lists can be months or years. Private prescriptions require an online clinical assessment with a UK-licensed prescriber, and costs typically range from £140–£320 per month depending on your dose. If you're struggling with weight loss or cost is a barrier, speak to your GP about NHS options, or explore whether a private prescription is feasible. Your prescriber can also discuss whether continuing Mounjaro or trying an alternative medication makes sense for your situation and budget.
- 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 Mounjaro take to show weight loss results?
Weight loss typically becomes noticeable between weeks 8 and 16, once you've reached an effective dose (usually 10 mg or higher). Clinical trials showed average weight loss of 15–21% of body weight over 72 weeks. Individual timelines vary — some people see results faster, others take longer. If you've been on a stable dose for less than 8 weeks, give it more time before assuming it isn't working.
What if I'm not losing weight despite being in a calorie deficit on Mounjaro?
Contact your prescriber. Lack of weight loss despite a calorie deficit and 8+ weeks on a stable dose may indicate you need a dose increase, or it's possible Mounjaro isn't the right medication for you. Your prescriber can review your response and recommend adjustments, including switching to an alternative weight loss injection if appropriate.
Can I access Mounjaro for free on the NHS in the UK?
Yes, Mounjaro is available on the NHS through specialist tier 3 weight management services, but access is limited and varies significantly by region. You'll need a GP referral and may face a long waiting list. Private prescription is available through online consultations and costs around £140–£320 monthly, depending on your dose.
Is Mounjaro or Wegovy more effective for weight loss?
Both medications are licensed and effective for weight loss in the UK. Mounjaro (tirzepatide) showed slightly higher average weight loss in clinical trials (around 20.9% at maximum dose) compared to Wegovy (semaglutide, around 14.9%). However, individual responses vary greatly — what works best depends on your personal health, side effects you experience, and prescriber guidance.
Should I stop taking Mounjaro if I'm not losing weight?
Don't stop without speaking to your prescriber first. Weight loss takes time, and you may not be on your optimal dose yet. If you've been on a stable dose for 8+ weeks with no progress, discuss dose adjustment or alternatives with your GP or prescriber rather than stopping suddenly.
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.