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 Aren't I Losing Weight on Mounjaro?
Weight loss on Mounjaro varies significantly between individuals, and if you're not seeing results, there are several reasons why — from dose titration timing to lifestyle factors. This guide explains what affects weight loss on this prescription injection, explores UK cost and access options, and helps you understand whether NHS or private access is the right route for you.
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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 Weight Loss on Mounjaro in the UK
Not everyone loses weight at the same rate on Mounjaro (tirzepatide), even though clinical trials showed an average weight loss of 15–21% body weight. Individual results depend on several factors: dose titration (you must be on your optimal dose for at least 4 weeks to see full effects), adherence to a reduced-calorie diet, physical activity levels, underlying metabolic health, and genetics.
- Clinical trials showed average weight loss of 20.9% at the maximum 15mg dose, but this was alongside strict dietary changes and increased exercise
- A weekly weight loss injection works best when combined with lifestyle modification — medication alone is not enough
- Some people experience a weight loss plateau after 6–12 months, which may require dose adjustment or lifestyle review
- Mounjaro's onset is gradual — significant weight loss typically takes 12–16 weeks to become apparent
If you're on a stable dose and seeing no progress after 12 weeks, speak to your prescriber about whether a dose increase or lifestyle review is needed.
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.
Mounjaro Cost in the UK — NHS vs Private Access
NHS access: Mounjaro is available through NHS tier 3 specialist weight management services following NICE approval, but access varies significantly by region. Many areas have waiting lists of several months to years. You must be referred by your GP and meet eligibility criteria (BMI 30+ or 27+ with weight-related health conditions).
Private access: Available through GPhC-registered online prescribing services following an online clinical assessment. Private costs typically range from £129–£320 per month depending on dose. A UK-licensed prescriber assesses your suitability before issuing a prescription. This route allows access without NHS referral or waiting lists, making it faster for many people seeking a weekly weight loss injection.
Calculate your expected weight loss with our free GLP-1 weight loss calculator above — it shows potential outcomes at different doses when combined with lifestyle changes. Check your current BMI using our BMI calculator to confirm eligibility for Mounjaro, and use our progress tracker to log your weight each week and identify whether you're progressing or plateauing.
- 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.
Why am I not losing weight after 4 weeks on Mounjaro?
Four weeks is the minimum time on each dose — you need at least 4 weeks (ideally 8–12 weeks) at your current dose before seeing meaningful weight loss. Mounjaro's effects are gradual. Ensure you're in a calorie deficit through diet and activity. If you're on the starting dose (2.5mg), weight loss typically accelerates once you reach higher maintenance doses (5mg+).
Does Mounjaro cost the same on the NHS and privately in the UK?
No. NHS prescription costs are standard (currently £11.90 per item on prescription, or free if exempt). Private costs vary by prescribing service and dose, typically £129–£320 per month. NHS access requires specialist referral and may involve waiting lists; private access is faster but requires upfront cost.
How long does a Mounjaro KwikPen last?
Each KwikPen contains 4 doses (4 weeks' supply) of the same dose strength. Once opened, a pen can be stored at room temperature for up to 30 days before disposal. You'll need a new prescription approximately every 4 weeks.
Can I switch from Mounjaro to Wegovy if I'm not losing weight?
Possibly, but only with prescriber guidance. Mounjaro (dual GIP+GLP-1) and Wegovy (GLP-1 only) work differently. If you're plateauing on Mounjaro, a dose increase is typically tried first. A prescriber can advise whether switching medications is appropriate based on your individual response.
What happens to my weight loss if I stop Mounjaro?
Weight often returns gradually if lifestyle changes aren't maintained. Mounjaro is not a permanent solution — it's a tool to support weight loss during active treatment. Most people maintain results through continued diet and exercise habits developed during treatment. Discuss long-term plans 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.