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
No Weight Loss in Week 2 of Mounjaro — Is This Normal?
If you're in your second week of Mounjaro and haven't noticed weight loss yet, you're not alone — and this is completely normal. Mounjaro (tirzepatide) works gradually, and the 2.5 mg starting dose is designed to allow your body to adjust to the medication. Weight loss typically becomes more noticeable after 4–8 weeks, as your dose increases during the titration schedule. Most people remain on the 2.5 mg dose for the full 4 weeks before escalating, so significant results shouldn't be expected immediately. This guide explains what happens in the early weeks and when you can realistically expect results.
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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 Weight Loss Takes Time on Mounjaro
Mounjaro is a dual GIP and GLP-1 receptor agonist, meaning it works on two hormone pathways to help regulate appetite and support feelings of fullness. However, these effects develop gradually as your body adjusts to the medication. The 2.5 mg starting dose is intentionally low — it's the adjustment dose, not the therapeutic dose. During weeks 1–4, your body is adapting to how the injection affects your stomach, appetite signals, and metabolism.
Clinical data shows that average weight loss becomes more apparent at higher doses and over longer timeframes. In the SURMOUNT-1 trial, average weight loss at 5 mg was approximately 15% of body weight over 72 weeks, but individual results varied significantly. Many people don't notice any change in the first 2 weeks, some see modest changes, and others see nothing until week 3 or 4. This variation is normal and does not predict your overall results.
- Week 1–4: Adjustment phase at 2.5 mg
- Week 5–8: Escalation to 5 mg begins
- Week 9+: Further escalation as prescribed
- Weeks 8–12: More noticeable results typically reported by users
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.
What to Focus On During Early Weeks
Rather than obsessing over the scales in week 2, focus on how the medication is making you feel. Many people report changes in appetite, food cravings, or how quickly they feel full — these are signs the medication is working, even if the scales haven't moved. Nausea, diarrhoea, or changes in digestion are also normal adjustment effects in the early weeks.
Track your progress using our free progress tracker and our GLP-1 weight loss calculator, which can help you set realistic expectations based on dose and timeframe. Continue following a reduced-calorie diet and staying physically active — Mounjaro works alongside lifestyle changes, not instead of them. If you have concerns about side effects or lack of change, contact your prescriber. They can confirm the medication is right for you and discuss whether your dose or approach needs adjusting.
- 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.
Is it normal to have no weight loss in week 2 of Mounjaro?
Yes, completely normal. Week 2 is during the 2.5 mg adjustment phase, and your body is still adapting. Most people don't see noticeable weight loss until weeks 4–8, when doses increase. Individual timelines vary — some see changes sooner, others take longer. If you have concerns, contact your prescriber.
What should I expect from a weekly weight loss injection like Mounjaro?
A weekly weight loss injection works by regulating appetite and fullness signals. Results develop gradually over weeks and months, not days. Clinical trials showed average weight loss of 15–21% body weight over 72 weeks at higher doses. Expect modest or no change in the first 2–4 weeks; more significant results typically appear after 8–12 weeks.
How does the Mounjaro dose titration schedule affect weight loss timing?
Mounjaro titration starts at 2.5 mg for 4 weeks, then escalates to 5 mg, 7.5 mg, and higher over subsequent weeks. Weight loss typically increases with each dose step. The low starting dose allows your body to adjust, minimising side effects. Most weight loss becomes noticeable after you've progressed through several dose increases.
Should I change my diet or exercise routine in week 2 of Mounjaro?
No — continue your current healthy habits. Mounjaro works alongside a reduced-calorie diet and physical activity, not instead of them. In early weeks, focus on sticking to your routine rather than expecting dramatic results. Your prescriber can advise if any adjustments are needed based on how you're tolerating the medication.
When should I contact my prescriber about no weight loss?
If you have persistent side effects, concerns about tolerance, or questions about your progress, contact your prescriber at any point. However, lack of weight loss in week 2 alone is not a clinical concern. They will assess your individual situation and may adjust your approach after you've completed the initial titration phase.
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.