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
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Not Losing Weight on Mounjaro — What You Should Know
If you've been taking Mounjaro and haven't noticed any weight loss yet, you're not alone — and there are several reasons why this might be happening. Weight loss on any medication, including this weekly weight loss injection, varies significantly between individuals. This guide explains common reasons for no weight loss on Mounjaro, when dose adjustments might help, and how to access treatment through NHS specialist services or private prescription routes in the UK. Understanding your options helps you make informed decisions about your weight management journey.
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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.
Why You May Not Be Losing Weight on Mounjaro
Weight loss on Mounjaro is not assured, and individual results vary considerably. Several factors can explain why you haven't lost weight yet:
- Too early in treatment: Some people need 8–12 weeks to see noticeable changes. Mounjaro works gradually, and your body continues to adjust as your dose increases.
- Dose too low: Starting doses (2.5 mg) are low intentionally — you may not be at your effective dose yet. Dose increases happen every 4 weeks, with maximum dose being 15 mg weekly.
- Calorie intake still too high: Mounjaro reduces appetite, but it doesn't eliminate the need for a reduced-calorie diet. Without a meaningful calorie deficit, weight loss won't occur.
- Medical factors: Thyroid issues, PCOS, medications (like antidepressants), or insulin resistance can reduce weight loss response.
- Metabolic adaptation: Your body may adapt to changes over time, resulting in plateaus.
Your GP or prescriber should review your progress at regular intervals and discuss whether mounjaro dose titration or dietary changes might help.
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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 Mounjaro in the UK — Cost and Routes
In the UK, you can access Mounjaro through two main routes. The NHS route is free at point of use if referred to a specialist tier 3 weight management service, though waiting lists vary by region and availability is limited. The private route requires an online consultation with a UK-licensed prescriber, with costs typically ranging from £150–£300 per month depending on your dose. Private prescriptions are dispensed by GPhC-registered pharmacies. Many people choose private access for faster availability, though NHS access may be an option if you meet local eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions). Whichever route you choose, a clinical assessment is required before prescription.
- 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 should I wait before deciding Mounjaro isn't working?
Most clinicians recommend at least 12 weeks of treatment at therapeutic doses before assessing effectiveness. Since doses increase every 4 weeks and maximum dose is 15 mg, you may not reach your optimal dose until week 20+. If you've been on a stable dose for 8+ weeks with no progress and no lifestyle barriers, discuss alternatives with your prescriber.
Should I switch from Mounjaro to Wegovy if I'm not losing weight?
Not necessarily. Both are prescription weight loss injections with different mechanisms — Mounjaro uses dual GIP+GLP-1 activation while Wegovy is GLP-1 only. If Mounjaro isn't working, the issue may be dose, lifestyle factors, or medical barriers rather than the medication type. Always discuss any switch with your prescriber. Use our GLP-1 weight loss calculator to compare potential outcomes at different doses.
Can I get Mounjaro on the NHS if I'm not losing weight privately?
NHS access requires referral to a specialist weight management service in your area and depends on local commissioning. If you've tried private treatment, document your progress with your GP — this may support an NHS referral. However, NHS availability varies significantly by region (ICB), and waiting times can be lengthy.
What dose adjustments might help if I'm not losing weight?
Your prescriber will typically increase your dose every 4 weeks if you tolerate it well, up to the maximum of 15 mg weekly. Dose escalation is the standard approach — jumping doses or speeding up increases is not recommended. Your prescriber may also explore whether constipation, nausea, or other side effects are preventing you from maintaining a reduced-calorie diet.
How does my BMI context affect expected weight loss on Mounjaro?
Clinical trials showed average weight loss of 15–21% of body weight, but individual outcomes vary widely based on starting weight, BMI, adherence, diet, and activity level. Use our free BMI calculator to track your current BMI and healthy weight range — this gives you a personalised target rather than relying on average figures. Your prescriber can discuss realistic expectations for your specific situation.
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.