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
How Do I Know If Mounjaro Is Working?
When starting Mounjaro (tirzepatide), you may wonder how to tell if the prescription injection is actually working for you. There are several practical ways to measure progress beyond just stepping on the scales. Understanding what to expect can help you assess whether Mounjaro is having the desired effect on your weight and health. This guide explains the key signs that Mounjaro is working and how to track your progress effectively using both physical measurements and how you feel day-to-day.
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.
Key Signs Mounjaro Is Working
The most obvious sign that Mounjaro is working is gradual weight loss over weeks and months. In clinical trials, participants using Mounjaro experienced average weight loss of 15–21% of their body weight at maximum doses, though individual results vary significantly. Weight loss is usually noticeable after 4–8 weeks of consistent use.
- Reduced appetite and food cravings — you may feel fuller after smaller meals or notice less desire to snack
- Changes in eating habits — foods you previously enjoyed may feel less appealing
- Improved energy levels — as your body begins to manage weight more effectively
- Better blood sugar control — if you have prediabetes or type 2 diabetes, blood glucose readings may improve
- Clothes fitting differently — a reliable non-scale indicator before weight changes show on the KwikPen
These changes happen at different rates for different people. Some notice appetite suppression within days; others take several weeks.
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.
How to Track Your Progress Accurately
Regular monitoring helps you confirm Mounjaro is working. Weigh yourself weekly at the same time of day (morning before eating is most consistent) and record the result — use our free progress tracker to log weekly weigh-ins and spot trends over time. Your GP or prescriber may also monitor your weight at appointments.
Beyond weight, ask your GP to check blood pressure, cholesterol, and blood sugar levels if you have risk factors — these often improve as weight decreases. Measure your waist circumference monthly, as this is a strong health marker independent of BMI. Take photos every 4 weeks to visually track changes you might not notice day-to-day.
Remember that weight loss is not always linear — some weeks you may lose weight, others plateau, and that is normal. Your prescriber may recommend dose titration (increasing your dose gradually through the stepping schedule: 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, to 15 mg) if you are not seeing expected progress, as individual response to tirzepatide varies. If you have concerns about whether Mounjaro is working after 8–12 weeks at an adequate dose, discuss this directly with your GP or the prescriber who issued your 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 does it take for Mounjaro to start working?
Most people notice reduced appetite within 1–2 weeks and visible weight loss within 4–8 weeks. However, this varies — some notice changes quickly, others take longer. Consistent use and following a reduced-calorie diet alongside the injection give best results.
What if I don't see weight loss after 8 weeks?
Weight loss can take time, and individual responses vary. Ensure you are following a calorie deficit diet and increasing physical activity. Your prescriber may increase your dose through the titration schedule. Discuss concerns at your next appointment — Mounjaro may not be right for everyone.
Can I check if Mounjaro is working without weighing myself?
Yes. Non-scale indicators include reduced hunger and cravings, clothes fitting better, increased energy, improved mood, and better blood sugar control. These are all valid signs of progress. Measure your waist circumference and take progress photos monthly.
Does Mounjaro vs Wegovy make a difference in how quickly you see results?
Mounjaro (tirzepatide) is a dual GIP/GLP-1 agonist; Wegovy (semaglutide) is a GLP-1 agonist only. Mounjaro showed average weight loss of 15–21% in trials; Wegovy showed approximately 14.9%. Individual response varies — some people respond better to one than the other, but this is unpredictable.
Should I expect side effects if Mounjaro is working?
Side effects and weight loss effectiveness are separate. Nausea, diarrhoea, and constipation are common in the first weeks but often improve as your body adjusts. These don't indicate whether Mounjaro is working — weight loss and appetite changes do. Report persistent side effects to your GP.
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.