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 Is Your Weight Loss Slow on Mounjaro?
If you're taking Mounjaro and noticing slower weight loss than expected, you're not alone—individual results vary significantly. Weight loss on this weekly weight loss injection depends on your current dose, how long you've been taking it, lifestyle factors, and your body's individual response. Understanding what's normal and when to seek guidance from your prescriber can help you manage expectations and stay motivated throughout your treatment 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.
Dose Titration and Expected Weight Loss Timeline
Mounjaro works gradually as your dose increases over several months. Many people experience minimal weight loss in the first 4 weeks on the starting dose of 2.5 mg—this is normal. The dose titration schedule means you increase to 5 mg in weeks 5–8, 7.5 mg in weeks 9–12, and potentially higher doses thereafter. Clinical trial data showed that significant weight loss typically accelerates around the 10–15 mg dose range. If you're still on a lower maintenance dose, slower progress may reflect that your body is still adjusting. Your prescriber will assess whether you're ready to increase your Mounjaro dose based on your tolerance and response. Using our GLP-1 weight loss calculator can help you project potential weight loss at different doses based on clinical trial outcomes.
- Weeks 1–4 (2.5 mg): Often minimal weight loss as the body adjusts
- Weeks 5–12 (5–7.5 mg): Weight loss typically becomes more noticeable
- Weeks 13+ (10–15 mg): Greater average weight loss observed in clinical trials
- Individual response varies—some people lose steadily, others plateau then accelerate
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.
Lifestyle Factors and Realistic Expectations
Mounjaro is not a standalone treatment—it works best alongside a reduced-calorie diet and increased physical activity. Slow weight loss may indicate that calorie intake is higher than needed, or that physical activity is limited. The NHS recommends losing weight at a sustainable rate of 0.5–1 kg per week; faster loss is possible with medication but not assured. Genetics, age, metabolic rate, and whether you've previously lost weight all influence how your body responds. Some people lose weight steadily; others experience plateaus followed by rapid loss. Tracking your progress with our free progress tracker alongside measuring non-scale victories—like improved energy, better sleep, or reduced hunger—can help you assess whether Mounjaro is working for you, even if the scales are moving slowly.
- 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 to see weight loss on Mounjaro?
Most people see minimal weight loss in the first 4 weeks on the starting 2.5 mg dose. Noticeable weight loss typically becomes more apparent once you reach 5–7.5 mg (weeks 5–12), with greater results often seen at higher doses. Individual timelines vary significantly—your prescriber can advise on what to expect based on your personal response.
Is slow weight loss normal on Mounjaro?
Yes, slow weight loss is common, especially in the early weeks or if you're on a lower maintenance dose. Weight loss depends on your dose level, how long you've been taking the injection, dietary adherence, and individual metabolism. If you've been on a stable dose for 8+ weeks with minimal progress, discuss dose escalation with your prescriber.
Should I increase my Mounjaro dose if weight loss is slow?
Do not self-increase your dose—this must be managed by your prescriber. Mounjaro has a structured 4-week minimum between dose increases. If you've been on your current dose for 8+ weeks without progress, ask your prescriber whether you're ready to escalate. Your tolerance to side effects and overall health are also considered.
What if my weight loss stops on Mounjaro?
Weight loss plateaus are common on any weight management medication. This may reflect that your body has adapted, or that calorie intake has drifted upward. Review your diet and activity levels with your prescriber or a dietitian. Dose escalation, if available, may help restart progress—your prescriber will advise.
Can I get Mounjaro through the NHS if weight loss is slow?
NHS access to Mounjaro (tirzepatide) is through specialist tier 3 weight management services following referral from your GP. Availability varies significantly by region. Your GP can refer you if you meet NHS eligibility criteria (BMI ≥30 or ≥27 with weight-related health conditions). Private prescribing is also available through UK-licensed online prescribers.
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.