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 taking Mounjaro but not seeing the weight loss results you expected, you're not alone. Weight loss plateaus are common, and the reasons vary—from dose adjustment needs to lifestyle factors, cost considerations affecting consistency, or simply individual variation in how bodies respond to tirzepatide. This guide explains what might be happening and your UK access options.
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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.
Understanding Why Weight Loss Slows on Mounjaro
Several factors can affect how well Mounjaro works for you. Dose timing matters: you may need to progress to a higher dose—the standard titration schedule increases your dose every 4 weeks, and some people require doses above 5 mg to see meaningful results. Weight loss typically plateaus after 3–6 months as your body adapts to the medication.
Lifestyle factors are crucial: Mounjaro works best alongside a reduced-calorie diet and regular physical activity. If your calorie intake hasn't changed or you've reduced exercise, results may stall. Individual variation is real: clinical trials showed that tirzepatide produces weight loss ranging from 15% to 21% of body weight on average—but some people lose less, while others lose more.
- Check that you're on an adequate dose for your body and health status
- Review your diet and activity levels with your GP or a dietitian
- Allow 12–16 weeks on your current dose before expecting plateau-breaking results
- Some people benefit from combining Mounjaro with structured weight loss programmes
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.
NHS vs Private Access — Cost & Consistency
In the UK, Mounjaro (tirzepatide) is available through both NHS specialist weight management services and private online prescribing. NHS access: if you qualify, there's no prescription cost, but waiting lists for tier 3 specialist services can be months or longer depending on your region, which may delay treatment or cause inconsistency. Private access: following a brief online clinical assessment with a UK-licensed prescriber, Mounjaro is typically available within 2–3 days from a GPhC-registered pharmacy.
Cost consistency is a factor some people overlook—if expense interrupts your Mounjaro course (doses typically cost £130–£200+ per month depending on your dose level), gaps in treatment can reset your progress. Using our free GLP-1 weight loss calculator can help you understand projected timelines and whether consistent access aligns with your expectations.
If you've paused or restarted Mounjaro: weight loss momentum may be slower on restart as your body re-adjusts. Consistency is vital for sustained results. Your prescriber can advise on the best path forward—whether that's increasing your dose, adjusting your lifestyle, or exploring whether a different GLP-1 medication like Wegovy or the weight loss approach itself is appropriate for you at this time. Check your BMI using our free BMI calculator to contextualise your progress against NHS healthy weight ranges.
- 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?
Most people begin to see modest weight loss within 2–4 weeks of starting, with more noticeable results after 8–12 weeks on a stable dose. However, individual timelines vary. Consistent lifestyle changes alongside the medication accelerate results. If you haven't seen progress after 12 weeks on your current dose, your prescriber may recommend dose escalation.
What if I'm on the maximum Mounjaro dose and still not losing weight?
If you're on 15 mg (the maximum dose) without meaningful weight loss after 16 weeks, discuss this with your prescriber. It may indicate that Mounjaro isn't the right medication for you individually, or that lifestyle factors need adjustment. Your GP can explore alternatives or adjust your weight management plan.
Does the cost of Mounjaro affect how well it works?
The cost doesn't affect the medication's action, but treatment interruptions due to cost can reset your progress. If private access is unaffordable, ask your GP about NHS specialist weight management services in your area, even if waiting lists are long. Consistency matters more than cost.
Can I switch from Mounjaro to Wegovy if Mounjaro isn't working?
Yes—your prescriber can assess whether switching to another GLP-1 medication like Wegovy (semaglutide) is appropriate. These are different medications with different mechanisms; some people respond better to one than the other. Your clinical assessment will guide which is right for you.
Should I give up on Mounjaro if I'm not seeing results after a few weeks?
No. Weight loss medications require 8–12 weeks minimum at an adequate dose to assess effectiveness. Rapid judgment leads to unnecessary switches. Work with your prescriber to ensure you're on the right dose, your lifestyle supports the medication, and you're tracking progress accurately using tools like our free progress tracker.
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.