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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How Do You Know If Mounjaro Is Working
When you start Mounjaro, it's natural to wonder if the medication is actually working for you. The signs that Mounjaro is working vary between individuals, but typically include reduced appetite, feeling fuller after smaller meals, and gradual weight loss over the first 4–8 weeks. Most people notice appetite changes before significant weight loss, and the medication continues to become more effective as your dose increases through the titration schedule. This guide explains what to expect and how to track your progress.
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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.
Early Signs Mounjaro Is Working
The first indication that Mounjaro is working is usually reduced appetite and changed food cravings, which many people notice within days or the first 1–2 weeks. You may find that you feel satisfied after eating smaller portions, experience less interest in certain foods (particularly high-fat or high-sugar items), and have fewer urges to snack between meals. Some people also report reduced food noise — constant thoughts about eating throughout the day.
Other early signs include:
- Nausea (very common on starting doses, usually improves within a few days to weeks)
- Changes in how quickly food leaves your stomach (gastric emptying), causing you to feel fuller longer
- Reduced thirst and increased thirst
- Changes in energy levels
- Improved blood sugar stability (if you have type 2 diabetes or prediabetes)
These early signs typically appear within the first week but can take 2–4 weeks to become consistent. Weight loss often follows appetite suppression — you may not see immediate scale changes, but reduced hunger and smaller portions will eventually lead to weight loss as you consume fewer calories.
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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.
Weight Loss Timeline & Dose Titration Effects
Significant weight loss typically becomes noticeable after 4–8 weeks of treatment, though this varies. The Mounjaro titration schedule is designed to increase your dose every 4 weeks (starting at 2.5 mg and escalating to 15 mg maximum), and weight loss often accelerates as you move to higher doses.
According to clinical trial data, average weight loss was approximately 15% of body weight at the 5 mg dose, rising to 20.9% at the maximum 15 mg dose over 72 weeks — though individual results vary significantly. Your GP or prescriber will monitor your progress at regular appointments (typically every 4–12 weeks). Use our free GLP-1 weight loss calculator to estimate potential weight loss at different doses, and our progress tracker to log weekly weigh-ins and track trends. Remember that weight fluctuates daily — looking at weekly averages gives a more accurate picture of whether Mounjaro is working.
- 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 quickly will I see weight loss on Mounjaro?
Most people notice appetite changes within 1–2 weeks, but visible weight loss typically takes 4–8 weeks to become noticeable. This varies by individual. Weight loss accelerates as your dose increases through the titration schedule. The medication works best alongside a reduced-calorie diet and increased physical activity.
What if I don't feel appetite suppression from Mounjaro?
Not everyone experiences dramatic appetite suppression — some people feel modest appetite changes. If you're not noticing effects after 4 weeks, discuss this with your prescriber. Dose adjustments, timing of injections, or dietary changes may help. Your GP can assess whether Mounjaro is working for you specifically.
Is nausea a sign that Mounjaro is working?
Nausea is a common side effect, particularly on starting and escalation doses, but it's not a sign of effectiveness — it's a sign that your body is adjusting. Nausea usually improves within days to weeks. It's separate from whether the medication is suppressing your appetite and supporting weight loss.
How do I know if my dose is high enough?
Your prescriber will assess how you're responding at each dose level during your regular appointments. If you're experiencing meaningful appetite reduction and gradual weight loss, your current dose is likely working. If progress stalls or you experience minimal appetite suppression, a dose increase (up to the maximum 15 mg) may be appropriate.
Can I compare my Mounjaro results to Wegovy results?
Mounjaro (tirzepatide) and Wegovy (semaglutide) are different medications with different mechanisms — Mounjaro is a dual GIP and GLP-1 agonist, while Wegovy is a GLP-1 agonist only. Clinical trial data shows slightly higher average weight loss with Mounjaro, but individual results vary so much that direct comparison isn't meaningful. Your results depend on your body, diet, and activity level, not on medication choice alone.
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.