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 Has Mounjaro Stopped Working For Me
If you've been taking Mounjaro and notice weight loss has plateaued or stopped, you're not alone — this is a common experience. Weight loss plateaus can happen for several reasons, from dose tolerance to lifestyle factors. This guide explains why Mounjaro may stop working as effectively, what your options are, and how to access alternatives like Wegovy through NHS or private prescription routes in the UK.
10,000+ calculations today · NHS-aligned thresholds · 100% free
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.
Weight Loss Plateaus and Mounjaro Tolerance
A weight loss plateau on Mounjaro (tirzepatide) can occur for several reasons. Dose tolerance is common — your body may adapt to your current dose over time, meaning the appetite-suppressing effect becomes less pronounced. You may be a candidate for a dose increase, which your prescriber can assess. Lifestyle factors also matter: if calorie intake has gradually increased or physical activity has decreased, weight loss naturally stalls even with medication. Additionally, metabolic adaptation occurs naturally during weight loss — your body requires fewer calories to maintain a lower weight. Some people also experience reduced effectiveness due to inconsistent injection timing, storage issues with the Mounjaro KwikPen, or underlying health changes. Try using our free GLP-1 weight loss calculator to reassess your expected outcomes at your current dose, and discuss with your GP or prescriber whether a dose increase might help.
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.
Alternatives: Wegovy and Cost Considerations
If Mounjaro is no longer effective, switching to Wegovy (semaglutide) is an option some people explore. Wegovy uses a different GLP-1 mechanism and may work better for some individuals. Private Wegovy prescriptions in the UK typically cost between £129–£200 per month depending on dose, with online consultations usually £15–£35. NHS access to Wegovy is limited to specialist weight management services, involving GP referral and potentially long waiting lists. Private routes are faster — often assessed and prescribed within days. Both medications require ongoing prescription and clinical assessment. Use our BMI calculator to confirm your current eligibility status, and discuss medication switching with your GP or a licensed prescriber to find the best option for your situation.
- 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.
Can I increase my Mounjaro dose if it's stopped working?
Possibly. Mounjaro doses range from 2.5 mg to 15 mg weekly. If you're below the maximum dose, your prescriber may increase it following a clinical assessment. Dose increases happen gradually — typically minimum 4 weeks apart. Not everyone needs the maximum dose, but some do. Discuss plateau concerns with your GP or prescriber.
How much does Wegovy cost privately in the UK?
Private Wegovy typically costs £129–£200 per month for medication, plus an online consultation fee of £15–£35. Costs vary by provider and dose (starting at 0.25 mg, maximum 2.4 mg). NHS access exists but is limited to specialist services with referral and waiting lists.
Why does weight loss stop even on medication?
Your body adapts metabolically during weight loss, requiring fewer calories to maintain. Lifestyle creep (increased eating, reduced activity) is also common. Dose tolerance can develop over months. Weight loss medications work best alongside consistent diet and activity changes — they're not a replacement for lifestyle effort.
Can I switch from Mounjaro to Wegovy on the NHS?
Switching between medications on the NHS requires GP involvement and specialist assessment. Access is through tier 3 weight management services with significant regional variation. Waiting lists can be long. Private switching is typically faster — assess eligibility with a licensed prescriber within days.
What should I do if Mounjaro isn't working anymore?
First, discuss with your prescriber — you may need a dose increase, or a review of lifestyle factors. Keep a food and activity log to identify changes. Consider switching medications if appropriate. Track your progress using our free progress tracker. Never stop medication abruptly — always consult your prescriber before making changes.
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.