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 12.5 mg?
Weight loss plateaus are common on Mounjaro, even at higher doses like 12.5 mg. There are several reasons this happens—ranging from your body adapting to the medication, to lifestyle factors, to whether you're at the right dose for you personally. Understanding these reasons, plus your options for adjusting your treatment or accessing the medication in the first place, can help you make informed next steps with your prescriber.
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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 for Weight Loss Plateaus on Mounjaro 12.5 mg
Body adaptation: Your body may adapt to the medication over time, particularly if you've been on Mounjaro for several months. Initial gradual weight management often slows as your body reaches a new equilibrium.
Calorie intake: Weight loss still fundamentally requires a calorie deficit. If your appetite suppression has worn off slightly, you may be consuming more calories without realising it. Our GLP-1 weight loss calculator can help you estimate expected outcomes based on your individual situation.
Dose plateau: At 12.5 mg, you're near the maximum Mounjaro dose, but some people require the full 15 mg dose to see continued results. Your prescriber may recommend increasing to the maximum dose if you've been stable at 12.5 mg for at least 4 weeks.
- Medication absorption may vary based on stomach health and gastric emptying
- Underlying conditions (thyroid issues, PCOS, diabetes) can affect weight loss rate
- Physical activity levels matter—diet alone may not produce further loss
- Sleep quality and stress directly impact weight management
Individual responses to GLP-1 receptor agonists vary significantly. Some people see steady loss throughout treatment; others plateau after reaching a new weight.
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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.
Accessing and Paying for Mounjaro in the UK
In the UK, Mounjaro access depends on your route. NHS access is through specialist tier 3 weight management services following a GP referral, though regional availability and waiting lists vary considerably. Private prescription access is available through registered UK prescribers who conduct online consultations—typically costing £129–£300+ per month depending on your dose.
Once you have a prescription, costs for a weekly weight loss injection at 12.5 mg are consistent across private providers. If cost is a barrier, discussing your situation with your prescriber or GP may reveal options—including whether NHS specialist services are available in your region, or whether dose adjustment could optimise both effectiveness and cost. Your GLP-1 medication should work alongside a reduced-calorie diet and increased physical activity for best results.
- 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.
Should I increase from 12.5 mg Mounjaro to 15 mg if I'm not losing weight?
Only your prescriber can advise. If you've been on 12.5 mg for at least 4 weeks with no weight loss and good tolerability, dose escalation to 15 mg may be considered. However, other factors—calorie intake, activity, underlying health conditions—should be explored first. Discuss this directly with your GP or the prescriber who issued your prescription.
How much weight should I expect to lose on Mounjaro 12.5 mg?
Clinical trial data shows Mounjaro helps people lose an average of 15–21% of body weight over time, but individual results vary significantly. Some people lose steadily; others plateau. Factors like your starting weight, diet consistency, physical activity, and genetics all influence your personal outcome. Use our GLP-1 weight loss calculator for a personalised estimate.
Can I get Mounjaro on the NHS in the UK?
Yes, Mounjaro (tirzepatide) is NICE-approved for NHS use through specialist tier 3 weight management services. However, availability varies by region, and referral wait times can be months or years in many areas. You'll need a GP referral. Private prescription routes are faster but involve upfront costs.
What's the difference between Mounjaro and Wegovy for weight loss?
Mounjaro (tirzepatide) is a dual GIP and GLP-1 receptor agonist; Wegovy (semaglutide) is a GLP-1-only agonist. In clinical trials, Mounjaro showed slightly higher average weight loss (~21% vs ~15%), but both require prescription and clinical assessment. The choice depends on your health profile, cost, and what your prescriber recommends.
Is weight loss supposed to continue the whole time I'm on Mounjaro?
No—weight loss typically follows a pattern: faster initial loss (weeks 1–16), then slower steady loss, then a plateau. This plateau is normal and doesn't mean the medication has stopped working. Your body is maintaining a new, lower weight. Continued lifestyle effort (calorie deficit, activity) helps sustain this new weight rather than regain.
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.